WO2025229332A1

WO2025229332A1 - Heat exchange assembly for stove

Info

Publication number: WO2025229332A1
Application number: PCT/GB2025/050927
Authority: WO
Inventors: Ronald Peter Binstead
Original assignee: Individual
Current assignee: Individual
Priority date: 2024-04-30
Filing date: 2025-04-30
Publication date: 2025-11-06
Anticipated expiration: 2026-10-30

Abstract

There is provided a heat exchange assembly for a domestic solid fuel-burning stove, the heat exchange assembly comprising: an inlet for receiving exhaust gas from combustion within the solid fuel burning stove; one or more heat exchange elements configured to extract most of the heat for external use from the exhaust gas and form cooled exhaust gas; an outlet for expelling the cooled exhaust gas from the heat exchange assembly; and a ventilation device coupled to the heat exchange assembly, wherein the ventilation device is configured to propel the cooled exhaust gas towards the outlet. There is also provided a smoke reduction device. There is further provided a solid fuel burning stove comprising: a combustion chamber having an opening for loading and unloading the combustion chamber with solid fuel; and a door for the opening that is slidably moveable between an open position and a closed position.

Description

Heat Exchange Assembly for Stove

Field of the Disclosure

The present disclosure relates to solid fuel-burning stoves. In particular, although not exclusively, the present disclosure relates to heat exchange assemblies, for solid fuelburning stoves for domestic use, and associated installation methods and methods of use.

Background

Solid fuel-burning stoves such as coal or wood-burning stoves have been a staple for heating and cooking in households for many years. Stoves used for domestic settings typically have a heat power output of up to 5kW for medium sized living areas. Larger domestic units might have a heat power output of up to 20kW.

However, traditional solid fuel-burning stoves face significant challenges related to both efficiency and pollution. These issues impact not only the environment but also the overall user experience.

The design of conventional wood stoves results in difficulty in efficiently convert fuel into useful heat. This inefficiency results in wasted energy and suboptimal performance. Emissions from wood-burning stoves contribute to air pollution, affecting both indoor and outdoor air quality. Harmful pollutants, such as particulate matter (PM), carbon monoxide (CO), and volatile organic compounds (VOCs), may be released during combustion. The on-going toughening of regulatory standards in some countries, and a growing environmental awareness concerning the use of stoves among the public, underscore the need for cleaner-burning stove technologies.

Some aspects of the present invention aim to address these efficiency and pollution issues associated with conventional wood-burning stoves. Further, according to some aspects of the disclosure, it is desirable to:

1) achieve as much as possible of the heat wasted in the flue but using limited resources.

2) retain the features people enjoy by seeing a natural fire.

Summary

The invention relates to a stove and associated devices and methods which may be for domestic use. A stove for domestic use may be rated for a maximum output power of 5 or 10 kW, for example. The stove for domestic use may have a combustion chamber with a volume of less than one of 50 L, 80L or 125L, for example.

Aspects of the invention relate to -

1) a heat exchange assembly that may provide nearly 100% heat recovery

2) a smoke removal device, which may be used for removal of smoke from the flue gas

3) a door that may prevent smoke getting into the room and associated methods. In general, a feature of an apparatus or method described with reference to one aspect may provided in combination with a feature of an apparatus or method described with reference to another aspect.

According to a first aspect of the invention, there is provided a heat exchange assembly for a solid fuel-burning stove, the heat exchange assembly comprising: an inlet for receiving exhaust gas from combustion within the solid fuel burning stove; one or more heat exchange elements configured to extract heat for external use from the exhaust gas and form cooled exhaust gas; an outlet for expelling the cooled exhaust gas from the heat exchange assembly; and a ventilation device coupled to the heat exchange assembly, wherein the ventilation device is configured to propel the exhaust gas towards the outlet.

The ventilation device may be configured to generate negative pressure to propel the exhaust gas towards the outlet.

The solid fuel-burning stove may be a domestic solid fuel-burning stove.

The ventilation device may be configured to propel the cooled exhaust gas towards the outlet.

The one or more heat exchange elements may be configured to extract most of the heat for external use from the exhaust gases and form cooled exhaust gas.

The at least one heat exchanging elements may comprise one or more metal or ceramic flue pipes, wherein the one or more heat exchange elements are configured to recover or extract at least 30%, 40%, 50%, 60%, 70%, 80% or 90% or up to 100% of the heat from the exhaust gas. The exhaust gas may also be referred to as flue gas.

The ventilation device may be arranged to cause negative pressure in the at least one flue pipe.

The negative pressure resulting from the ventilation device ensures the stove is inherently safe and automatically extinguishes itself or shuts itself down in case of a failure of the ventilation means.

The one or more flue pipes may be in any orientation.

The heat exchanger and ventilation device may be configured to enable the exhaust the cooled exhaust gas to have a temperature less than 60 degrees centigrade when the inlet is fed with exhaust gas at a temperature of between 250 and 600 degrees centigrade, or between 120 and 600 degrees centigrade.

The one or more metal or ceramic tubes/pipes may be situated in the room; heat being recovered by natural convection and radiation or assisted by ambient air being blown over them by a fan. The one or more metal tubes/pipes are readily available low cost, 1 inch diameter stainless steel exhaust tubes, wound in a loose spiral and fitted underneath the combustion chamber, being replaced and recycled after a long period of use.

The heat exchange assembly may comprise a plurality of heat exchange elements placed in succession to cool the exhaust gas. The heat exchanger may comprise a heat pump.

The plurality of heat exchange elements may extend within the at least one flue pipe. The plurality of heat exchange elements may extend external to the at least one flue pipe.

The first of the plurality of heat exchange elements may be comprised to recover most of the initial, very hot, heat, and another heat exchange element may be configured to recover any residual heat not recovered by the first heat exchange element.

The ventilation device is a mechanical or electrical device.

The ventilation device comprises a fan powered by one or more of mains electricity, battery, solar cells, or wind power or, once the stove is burning hot, by a Sterling Engine or Peltier Effect device. The assembly may be configured to be coupled in-line between a standard solid fuel burning stove and a standard flue liner.

The outlet of the heat exchange assembly may be configured to be coupled to an existing chimney or a hole in the wall via a tube. The flue may have a diameter of between 2 inches and 6 inches or more.

The heat exchange mechanism may comprise means to circulate water to cool the exhaust gas.

The heated water may be circulated through a radiator system to heat a room. The heat exchange mechanism may further comprise means for replenishing the circulating water and a water outlet for tapping the heated water for use elsewhere, such as in a domestic appliance.

The heat exchange assembly may further comprise, at the inlet, a pre heat-exchange section comprising any one of a hot metal, ceramic, or catalysing scrim, thereby creating turbulent gas flow conditions that enable secondary/tertiary combustion, burning many of the exhaust gas particulates.

The heat exchange assembly may further comprise, at the outlet, a particulate filter for filtering out any remaining particles, including micro particles. The cool exhaust gas may be sucked through this filter by the ventilation means.

The heat exchange assembly may further comprise further particulate removing, gas cleaning or carbon dioxide removing means.

The ventilation means may be configured to be controlled manually, by timers, by feedback mechanisms, or by mobile phone/computer, enabling the fire to be controlled and extinguished directly by the user or by remote control.

In another aspect according to the present invention, there is provided a stove for burning solid fuel, comprising: a combustion chamber; and the heat exchange assembly of any preceding claim; wherein the flue inlet is in fluid communication with the combustion chamber to receive the exhaust gas from the combustion chamber. The stove may have the visual, functional and psychological advantages of a standard domestic solid fuel burning stove.

The stove may comprise an air inlet. In particular, the combustion chamber may comprise an air inlet. The air inlet may draw air into the combustion chamber from an external source separate from the room in which the stove is situated, thus keeping the stove a closed system. The air inlet may comprise an air inlet tube which may be accommodated by a hole in the wall of the building in which the stove is installed.

The stove may be readily movable and may be fitted anywhere in or outside the house; possibly using a secondary paper, plastic, or aluminium foil tube to vent the cool exhaust gas out of the house.

The air inlet tube I pipe section and the outlet of the heat exchange assembly may be combined to form a "balanced flue" system with the outgoing exhaust gas pre-heating the incoming cold air and the incoming cold air cooling the exhaust gas.

The outlet may comprise a flue outlet pipe section, and the air inlet pipe section and flue outlet pipe section may be concentric, thus forming a coaxial pipe so as to form a "balanced" flue system with the outgoing exhaust gas pre-heating the incoming cold air and the incoming cold air cooling the exhaust gas.

The heat exchanger may comprise a portion with an outer tube and an occluded inner tube arranged such that the exhaust gas passes between the inner and outer tubes. The heat exchanger may be at least partially surrounded with a mesh framework, or other fire guard.

In yet another aspect according to the present invention, there is provided a method of retrofitting a heat exchanger to a stove installation, comprising: removing a section of flue pipe from a stove installation; and coupling the inlet and outlet of the heat exchange assembly to respective openings in the stove installation created by the removal of the section of the flue pipe.

The following examples are also disclosed.

1) A heat exchanger is used to extract nearly 100% of the heat from the exhaust gas in a domestic wood burning stove.

2) As example 1 where hot exhaust gas is sucked though long metal pipes. 3) As examples 1 and 2 where the pipes are cooled by an external fan.

4) As example 1 where air and exhaust gas is mechanically sucked through the stove with a small fan or bellows.

4a) As example 1 where are and exhaust gas are sucked through the stove with a small fan, bellows or Venturi effect device such as a Venturi tube, for example.

5) As the previous examples where the hot exhaust gas is sucked through filter material, such as Stainless Steel scourers and Wire wool.

6) As example 1 where a very fine micro-filter is used to filter out microscopic particles at the cold end of the heat exchanger.

7) As Example 1 where the cooled exhaust gas is sucked through wet scrubbers to remove fine particulates and carbon dioxide.

In examples where the ventilation device(s) work downstream from the heat exchanger, they will not be exposed to intense heat, so could be made from low temperature materials or a wide range of materials such as metal, plastic, ceramic, glass, or wood. A bellows could be made of wood and leather.

The following clauses are also disclosed.

Clause 1. A heat exchange assembly for a solid fuel burning stove, the heat exchange assembly comprising: a flue pipe section having at least one inlet for receiving exhaust gas from combustion within the solid fuel burning stove; a middle section consisting of one or more heat exchanging elements for recovering between 60% and 100% of heat in the exhaust gas; the flue pipe section further having an outlet for expelling the cooled exhaust gas from the flue pipe section by means of a ventilation device coupled to the flue pipe section and configured to generate a negative pressure to propel the exhaust gas towards the outlet of the flue pipe section.

2. As Clause 1 where the ventilation means is fitted in the cooled exhaust gas zone, at the outlet of, or after the flue pipe section, and generates a negative pressure to suck the exhaust gas through the flue pipe and the heat exchanger.

3. As Clauses 1 where the flue can be in any orientation.

4. As any of the previous clauses where the ventilation means is a mechanical or electrical device. 5. As clause 4 where the ventilation means is a fan, powered by one or more of the following - mains electricity, by battery, by solar or wind power or - once the stove is burning hot, by a Sterling Engine or Peltier Effect.

6. As clause 1 where the heat exchange mechanism is an in-line retro-fit between a standard stove and a standard flue liner.

7. As any of the previous clauses where the cooled exhaust gas exits the building through the existing chimney or a hole in the wall via a tube.

8. As clause 1 where the system is "closed"; the air comes through a hole in the wall and enters the combustion chamber via a tube.

9. As clauses 7 and 8 where the air inlet and exhaust gas outlet are combined to form a "balanced" flue, with the outgoing exhaust gas pre-heating the incoming cold air and the incoming cold air cooling the exhaust gas.

10) As any of the previous clauses where the stove has the visual, functional and psychological advantages of a standard domestic solid fuel burning stove.

11) A heat exchanger of clause 1 where the exhaust gas is cooled by water, and the heated water is used for domestic purposes or circulated through a radiator to heat the room.

12) A combustion chamber of clause 1 wherein the fuel burning surface is relatively horizontal and a separate relatively vertical "blind" chimney superstructure that sits on the fuel burning surface, with a relatively air-tight seal between the two; the "blind" chimney being hinged, along one edge of the fuel burning surface, or able to be raised from, and lowered onto the fuel burning surface, using a raising mechanism with a heat resistant handle; the fire being fed air from the room, in a manner similar to a standard solid fuel burning stove, when the "blind" chimney is raised, the system temporarily being "open"; one or more flue pipes, opening relatively high up inside the "blind" chimney (even if the "blind" chimney is raised) sucking exhaust gas upwards from the fire into the chimney cavity, possibly through a secondary burning zone, then downwards through the pipes, either round or through the surface that supports the fire and entering the heat exchanger means outside the combustion chamber. 12A) A combustion chamber of clause 1 wherein the fuel burning surface is flat or curved and relatively horizontal, and a separate relatively vertical, detachable "blind" chimney superstructure that sits on the fuel burning surface, with a relatively air-tight seal between the two.

12B) A combustion chamber of clause 1 wherein the fuel burning surface is relatively horizontal and a separate relatively vertical "blind" chimney superstructure that sits above the fuel burning surface; the "blind" chimney being able to be raised from, and lowered onto the fuel burning surface, using a raising mechanism with a heat resistant handle; the fire being fed air from the room, in a manner similar to a standard solid fuel burning stove, when the "blind" chimney is raised, the system temporarily being "open"; one or more flue pipes, opening relatively high up inside the "blind" chimney (even if the "blind" chimney is raised) sucking exhaust gas upwards from the fire into the chimney cavity, possibly through a secondary burning zone, then downwards through the pipes, either round or through the surface that supports the fire and entering the heat exchanger means outside the combustion chamber.

13) As Clause 1 where more than one heat exchange method is used, the first to recover most of the hot heat, another to recover any residual heat not recovered by the first method.

14) As Clause 1 where there is a pre heat-exchanger section at the inlet of the flue section containing a hot metal, ceramic or catalysing scrim, creating turbulent gas flow conditions that enable secondary/tertiary combustion, burning many of the exhaust gas particulates.

15) As Clause 1 where there is a post heat-exchanger section at the outlet of the exhaust gas section containing a micro-filter for filtering out any remaining particles, including micro particles; cool exhaust gas being sucked through this filter by the ventilation means.

16) As Clause 15 where there are further particulate removing, gas cleaning and carbon dioxide removing means.

17) As all the previous clauses, except clause 6 where the stove is readily movable and can be fitted anywhere in or outside the house; possibly using a secondary paper, plastic or aluminium foil tube to vent the cool exhaust gas out of the house. 18) As all the previous clauses where negative pressure venting ensures the stove is inherently safe and automatically extinguishes itself in case of a failure of the ventilation means.

19) As all the previous clauses wherein the ventilation means is controlled manually, by timers, by feedback mechanisms, or by mobile phone/computer, enabling the fire to be controlled and extinguished directly by the user or by remote control.

20) As Clause 1 where the flue is the heat exchanger, being composed of one or more long metal tubes situated in the room; heat being recovered by natural convection and radiation or assisted by ambient air being blown over them by a fan.

21) As clause 20 where the metal tubes are readily available low cost, 1 inch diameter stainless steel exhaust tubes, wound in a loose spiral and fitted underneath the combustion chamber; being replaced and recycled after a long period of use.

22) As in all the other clauses where the ventilation means is a Cyclonic suction device, with or without a HEPA filter.

According to a further aspect of the disclosure, there is provided a heat exchange assembly for a solid fuel burning stove, the heat exchange assembly comprising: a flue pipe section having an inlet for receiving exhaust gas from combustion within the solid fuel burning stove, the flue pipe section further having an outlet for expelling the exhaust gas from the flue pipe section; a ventilation device coupled to the flue pipe section and configured to generate a negative pressure to propel the exhaust gas towards the outlet of the flue pipe section.

The flue pipe section may comprise an elongated or coiled section providing a means for exchanging heat between the exhaust gas within the flue pipe section and the surroundings of the flue pipe section.

The heat exchange assembly may comprise one or more heat exchange elements in thermal contact with the flue pipe section.

The one or more heat exchange elements may comprise radiator plates or cooling fins extending from the flue pipe section to dissipate heat from the heat exchanger. The solid fuel burning stove may further comprise a second ventilation device configured to circulate air over the flue pipe section and/or one or more heat exchange elements.

The heat exchange assembly may comprise a plurality of flue pipe sections, each flue pipe section having a respective inlet for receiving exhaust gas from the combustion within the solid fuel burning stove and each flue pipe section further having an outlet for expelling the exhaust gas from the respective flue pipe section.

The outlets of the plurality of flue pipe sections may converge to expel exhaust gas from the flue pipe sections via a single ventilation device.

The ventilation device may be coupled to the outlet of the flue pipe section.

The ventilation device may be arranged to suck the exhaust gas through the flue pipe section.

The ventilation device or second ventilation device may comprise a fan, such as an electrical fan, or a bellows.

The heat exchange assembly may further comprise or may be configured to receive one or more particulate filters positioned within the flue pipe section. The one or more particulate filters may be positioned between the inlet of the flue pipe section and the one or more heat exchange elements. The one or more particulate filters may be positioned between the one or more heat exchange elements and the ventilation device. The one or more particulate filters may be positioned between the ventilation device and the outlet of the flue pipe section. The one or more particulate filters may comprise a micro-particulate filter or a highly compressed filter. The one or more particulate filters comprises metallic I metal alloy scourers or wire wool or wet scrubbers.

According to a further aspect of the disclosure there is provided a stove for burning solid fuel, comprising: a combustion chamber; and the heat exchange assembly, wherein the flue pipe section is in fluid communication with the chamber to receive the exhaust gas from the combustion chamber. The inlet of the flue pipe section may be positioned within the combustion chamber. The flue pipe section may extend downwardly within the chamber and the outlet of the flue pipe section may be situated outside of the combustion chamber.

According to a further aspect of the disclosure there is provided a smoke reduction device for removing smoke produced by a stove, comprising: a device inlet configured to receive exhaust fluid containing smoke from the stove; a device outlet for expelling exhaust fluid from the device; and a heat source between the device inlet and device outlet and arranged to burn at least some smoke from the stove so that the smoke content of the exhaust fluid expelled from the burner outlet is reduced.

The smoke reduction device may be used with a solid fuel burning stove. Alternatively, the smoke reduction device may also be used for any source of smoke, whether from solid fuel, liquid fuel, or gas. For example, it may also be used with the exhaust from a petrol or diesel engine.

The heat source may be arranged such that carbon monoxide or solid particulate content of the exhaust fluid that is expelled from the burner outlet is reduced. The heat source may be one of: a burner, a smokeless solid fuel burner, a gas burner, a liquid fuel burner, and an electrical heating element. The heat source may be configured to generate a negative pressure thereby drawing the exhaust gas though the burner inlet.

According to a further aspect of the disclosure there is provided a stove for burning solid fuel comprising: a combustion chamber; and a smoke reduction device described herein, wherein the burner inlet of the smoke reduction device is in fluid communication with the combustion chamber to receive the exhaust gas from the combustion chamber.

The stove may further comprise a heat exchange assembly comprising: an heat exchange inlet for receiving exhaust fluid from combustion within the solid fuel burning stove; one or more heat exchange elements configured to extract heat for external use from the exhaust gas and form cooled exhaust fluid; a heat exchange outlet for expelling the cooled exhaust fluid from the heat exchange assembly; and a ventilation device coupled to the heat exchange assembly, wherein the ventilation device is configured to propel the exhaust fluid towards the heat exchange outlet.

The heat exchange assembly inlet and/or the device inlet may be in fluid communication with the combustion chamber to receive the exhaust fluid from the combustion chamber.

The ventilation device may be arranged to receive exhaust fluid that has passed through the smoke reduction device. The ventilation device may be arranged to receive cooled exhaust fluid that has passed through the heat exchange assembly. The heat exchange assembly may be arranged to receive exhaust fluid that has passed through the smoke reduction device. The smoke reduction device, ventilation device and heat exchanger may be provided along a single fluid flow path. The stove may further comprise a controller. The controller may be configured to control operation of the smoke reduction device in accordance with a smoke level.

According to a further aspect of the disclosure there is provided a method of reducing smoke expelled from a solid fuel burning stove, comprising: activating the heat source of the smoke reduction device of claim 1; and subsequently, igniting a stove fire in a combustion chamber of the solid fuel burning stove.

The heat source of the smoke reduction device may be deactivated in response to any of: the stove fire temperature exceeding a temperature threshold; the time since igniting the stove fire has exceeded a time threshold; and a visual indication that the smoke produced by the stove fire has reduced.

Fuel may be added underneath the stove fire such that the fuel is not in direct contact with the fire. After a period of time, the fuel may be moved into direct contact with the fire. The ventilation device of the heat exchange assembly may be activated.

According to a further aspect of the disclosure there is provided a solid fuel burning stove comprising: a combustion chamber having an opening for loading and unloading the combustion chamber with solid fuel; and a door for the opening that is slidably moveable between an open position and a closed position. The door may be arranged to slidably move in a linear direction. The door may be arranged to slidably move along a vertical axis. The door may be slid upwards when in use to move from the closed position to the open position. The door may be arranged to slidably move along a plane of the door. The door may comprise a door panel. The door may comprise one or more tracks or guides. A pair of tracks or guides may be provided in parallel. The door panel may be configured to slide along, and between, the pair of tracks or guides. The door panel may comprise tempered glass. The tracks may be configured to receive an opposed pair of parallel edges of the door. The door may be rectangular. The opening may be rectangular. The door may be pivotably coupled to slidably move along the plane of the door.

The door may be arranged such that, when the door is moved into the open position, air is sucked into the combustion chamber. The opening may have an area greater than 100 cm² when in the open position. The stove comprises one or more sealing elements. The one or more sealing elements may be provided adjacent to the opening. The one or more sealing elements may be configured to engage with the door to form a seal. The door may be slidably moveable relative to the sealing elements.

In the closed position, the door may be sealed to prevent air from entering the stove such that fire cannot be sustained in the stove. The door may comprise a handle along any of: a bottom edge or a top edge.

A sealing element may be disposed at each of a top edge and a bottom edge of the opening. The placement may be such that, in the closed position, the top and bottom seals are engaged with the door. In the one or more open positions, the top seal maintains engagement with the door as the door is moved along the vertical axis.

A feature described in relation to a particular example, embodiment, aspect, claim or figure may be provided in combination with any other example, embodiment, aspect, claim or figure.

In general, the technology disclosed herein is equally applicable to: a) Open fires, either in an open fireplace, or outdoors, such as a BBQ. b) Other fuel burning fires, including solid, liquid or gas fuelled fires.

Brief Description of Drawings

The disclosure will now be discussed with reference to the drawings, in which - Figure 1 illustrates a schematic diagram of a conventional stove for burning solid fuel;

Figure 2 illustrates a schematic diagram of an improved stove for burning solid fuel;

Figures 3A to 3D illustrates schematic diagrams of arrangements for improved stoves for burning solid fuel;

Figure 4 illustrates a schematic diagram of a further arrangement for a heat exchanger in use on an improved stove;

Figure 5A illustrates a schematic diagram of a further arrangement for a heat exchanger in use on an improved stove;

Figure 5B illustrates a schematic diagram of a connector for retro-fitting the heat exchanger onto the improved stove shown in Figure 5A;

Figures 6 and 7 illustrate views of an example of an improved stove;

Figure 8 illustrates another example of an improved stove; and

Figures 9A and 9B illustrate schematic diagrams of a further arrangement for a heat exchanger in use on an improved stove;

Figure 10A illustrates another example of an improved stove without a chimney fitted ;

Figure 10B shows the same stove as Figure 10A with the chimney fitted over the fire;

Figure 11A illustrates yet another example of an improved stove;

Figure 11B shows a rear view of the same stove as Figure 11A.

Figure 12a illustrates a schematic block diagram of a smoke removal device;

Figure 12b illustrates an example smoke removal device;

Figure 13 illustrates a stove arrangement with various positions for placing a smoke reduction device;

Figure 14A illustrates smoke at the outlet of a stove with a smoke reduction device that is inactive;

Figure 14B illustrates the stove of Figure 14A with a reduced level of smoke at the outlet of the stove with the smoke reduction device when the smoke reduction device is active;

Figure 15A illustrates an example of a smoke reduction assembly configured with a stove;

Figure 15B illustrates another example of a smoke reduction assembly configured with a stove;

Figure 15C illustrates yet another example of a smoke reduction assembly configured with a stove;

Figure 15D illustrates an alternative flue input for a smoke reduction assembly; Figure 15E illustrates a stove retro-fitted with a smoke reduction assembly;

Figure 15F illustrates an example of a stove configured with a smoke reduction assembly, a heat exchange assembly, and a ventilation device;

Figure 16 illustrates a schematic diagram of a fluid flow reversal mechanism;

Figure 17A illustrates a schematic diagram of a stove with a heat exchanger;

Figure 17B illustrates a schematic diagram of the stove with the heat exchanger of Figure 17A and a further smoke removal device;

Figure 17C provides an expanded view of the smoke removal device of Figure 17B;

Figure 17D illustrates a schematic diagram of a stove and at least a portion of another heat exchanger and the smoke removal device of Figure 17B;

Figure 17E illustrates a schematic diagram of a stove with a further heat exchanger and the smoke removal device of Figure 17B;

Figure 17F shows a photograph of a prototype retro-fit heat exchanger, in which the heat exchanger sits beside the stove;

Figure 17G shows a photograph of another prototype retro-fit heat exchanger, in which the heat exchanger sits beside the stove;

Figure 17H illustrates a schematic diagram of a side view of a stove with a rearmounted flue pipe with a smoke burner;

Figure 18A illustrates a series of views of a stove that has been retrofitted with a sliding door;

Figure 18B illustrates a series of views of a stove with a sliding door; and Figures 19A and 19B illustrate a stove comprising an insert.

Description

Figure 1 illustrates a schematic diagram of a stove 10 for burning solid fuel such as wood or coal in a domestic setting. The stove 10 is illustrates in the orientation of its intended use and the use of terms such as "top" and "bottom" shall be construed accordingly.

The stove 10 has a combustion chamber 12 for receiving the solid fuel. The combustion chamber 12 has a base plate 14 with an air inlet 16.

The stove 10 further comprises a flue pipe 18. The flue pipe 18 has a flue inlet 20 and a flue outlet 22. The flue inlet 20 of the flue pipe 18 is coupled to the top of the combustion chamber 12.

The solid fuel may be received through a door (not shown) of the stove 10. In use, the user places combustible solid fuel within the combustion chamber 12 and sets it alight. Air 24 is drawn by the fire from an exterior of the combustion chamber, through the air vent 16 and into the combustion chamber. Within the combustion chamber 12, the air is heated by the combustion process and rises such that it leaves the combustion chamber 12 and enters the flue pipe 18 via the flue inlet 20. Within the flue pipe 18, the exhaust gas from the combustion chamber remain hotter than the ambient air outside of the flue pipe 18. As such, the exhaust gas within the flue travel up the flue pipe 18 from the flue inlet 20 and leave the flue into the external environment via the flue outlet 22.

The efficiency of conventional wood burning stoves is typically about 70% to 80% due to the reliance on rising hot gas to suck air through the burning wood. Therefore a 5 KW fire may lose one or two KW of heat up the flue. Some attempt is often made to capture some of this heat by increasing the exposed surface area of the flue pipe and use of Peltier Effect fans to blow the heat from the flue pipe into the room, but there is a limit to how much heat can be extracted before the exhaust gas stops rising, and the fire goes out. The need for an unobstructed flue limits any passive particulate filters that can be placed in the flue pipe.

Wood burning stoves also emit the majority of particulates as the fire is starting, especially with damp and green wood. The heat is not strong enough to drive off the water and burn the damp wood without a lot of smoke.

The environmental issues concerning wood burning stoves have become so severe that they are being banned in new builds in Scotland from 2025 and may be banned in many other countries soon.

Figure 2 illustrates an improved stove 100 according to an aspect of the present disclosure. Corresponding reference numerals are used between the figures in order to identify the components of the stove described previously with respect to figure 1, which in general will not be discussed further.

The improved stove 100 of figure 2 differs from the stove described previously with reference to figure 1 in that the improved stove has a modified flue provides a heat exchange assembly 118.

The heat exchange assembly 118 comprises a heat exchanger 102 and a ventilation device 104. The heat exchanger 102 and the ventilation device 104 are each coupled to and in fluid communication with the flue pipe 18. For ease of description, in this example the heat exchange assembly 118 is described as being installed within the flue pipe 18. The heat exchange assembly may be provided in a section of flue pipe that is coupled to one or more other flue pipes and/or the combustion chamber. Components of the heat exchange assembly may be provided separately from a flue pipe for retrofitting an existing flue pipe installation.

The heat exchanger 102 is provided between the inlet 20 and the outlet 22 of the flue pipe 18. The heat exchanger 102 enables heat within the exhaust gas to be transferred to the ambient environment outside of the flue pipe 18. Removing the heat from the exhaust gas causes the self-propulsion of the exhaust gas to the exterior of the flue to stall. The ventilation device is provided to draw or propel the exhaust gas through the flue pipe 18 so that the cooled exhaust gas maybe expelled from the flue pipe 18 and maintaining fluid flow to allow combustion of the fuel within the combustion chamber 12. In this way, a substantial portion of the heat of the exhaust gas can be recovered whilst allowing combustion to be maintained.

The operation of the heat exchange assembly may be assessed by measuring the temperature of the exhaust gases at different points along the assembly. The exhaust gas temperature may be measured by one or more thermocouples or EGT (Exhaust Gas Temperature) sensors mounted in the exhaust gas stream. The proportion of heat energy I thermal energy extracted from the exhaust gas by the one or more heat exchange elements may be estimated by taking temperature measurements at the inlet and outlet of the heat exchange assembly (or before and after the one or more heat exchange elements). A change in internal heat I thermal energy of an ideal gas is directly proportional to the change in temperature of an ideal gas. Therefore, the percentage temperature difference between the exhaust gas temperature at the inlet and outlet of the heat exchange assembly gives an approximate indication of heat energy extracted. A more accurate estimate of the heat I thermal energy extracted from the exhaust gases would account for pressure of the exhaust gases at the inlet and outlet, and the work done by the negative pressure of the ventilation device.

For example, the heat exchanger and ventilation device may be configured to enable the exhaust the cooled exhaust gas to have a temperature less than 30 degrees Celsius above the ambient temperature when the inlet is fed with exhaust gas at a temperature of between 200 and 600 degrees Celsius (for example 400 °C) above the ambient temperature. In a preferred embodiment such as that illustrated in figure 2, the ventilation device is provided downstream, with reference to the exhaust gas flow, from the heat exchanger 102. In this way, the exhaust gas is substantially cooled by the time they reach the ventilation device 104 so the thermal requirements of the materials used to construct the ventilation device 104 may be reduced.

In this example, the ventilation device 104 is provided adjacent to the outlet 22 of the flue pipe 18. The arrangement of the ventilation device 104 causes negative pressure to be generated upstream of the fan with respect to the combustion gas flow.

Instead of relying on the fact that hot air rises, air and exhaust gas can be pulled through the fire with the ventilation device 104, which may be provided by a fan or bellows. The ventilation device 104 may be electrically or mechanically operated. Pulling the exhaust gas through the fire is more failsafe than forcing air through the fire as the former relies on negative pressure in the combustion chamber and the latter relies on positive pressure. With negative pressure, any leakages in the combustion chamber will keep the smoke within the stove, whereas positive pressure will force smoke and gas into the room.

The Efficiency of Domestic Wood and Coal burning stoves may be improved by extracting almost all the waste heat in the exhaust gas by means of a heat exchanger in some examples. Exhaust gas is mechanically forced through the heat exchanger, particulate filter and possibly gas scrubber by various means.

Various other arrangements of stoves according to the present disclosure are described below with reference to figures 3A to 3D.

Figure 3A illustrates a stove 300 that is similar to the stove described previously with reference to Figure 2 and further comprises a filter 206. The filter 206 is provided adjacent to the flue inlet 20 of the flue pipe 18. In this example, the filter 206 is provided between the heat exchanger 102 and the flue inlet 20. Alternatively, a smoke removal device may be provided instead of, or in addition to, the filter.

Figure 3B illustrates a further stove 200' according to the present disclosure. The stove 200' differs from the stove 200 described previously with reference to figure 3A in that the filter 208' is located closer to the flue outlet 22 of the flue pipe 18. In this example, the filter 208' is provided between the heat exchanger 102 and the ventilation device 104. Figure 3C illustrates a further stove 200" according to the present disclosure. The stove 200" is similar to that described previously with reference to figure 2 and further includes a first filter 206 and a second filter 208. The first filter 206 is arranged as described previously with reference to figure 3A. The second filter 208 is positioned as described previously with reference to figure 3B.

Figure 3D illustrates a further stove 300. The stove 300 is similar to the stove described previously with reference to figure 2 except the ventilation device 104' is positioned closer to the flue inlet 20 than the flue outlet 22. In this example, the ventilation device 104' is provided between the flue inlet 20 and the heat exchanger 102. In general, the ventilation device 104' maybe provided at any position along the flue pipe 18. However, the arrangement shown in Figure 3D may be considered to be a sub-optimal arrangement because the ventilation device 104' would be exposed to very high temperatures and therefore have higher requirements for its material properties than in examples in which the ventilation device is provided further downstream and is exposed to cooled exhaust gases.

Advantages of mechanically sucking air and exhaust gas through the fire include -

1) Nearly all the heat can be extracted from the exhaust gas by means of a heat exchanger. A 5 Watt fan can save 1000 Watts (or more) of heat and reduce greenhouse gas emissions by 20 to 30%.

2) Extracted exhaust gas is only slightly above room temperature when it leaves the heat exchanger, so a heat resistant flue liner is not needed.

3) The flue does not need to be vertically above the stove, but can go in any direction, even downward, and can exit the building though a narrow pipe in the wall. The chimney stack itself can be eliminated, leaving more room in the house.

4) A lot of air is sucked through the fire from the very start, making initial lighting quicker, thereby minimising the amount of particulates produced at the start of the fire.

5) The heat exchanger pipes can initially be routed through the fire, thereby facilitating secondary or tertiary burning of particulates within the pipe.

6) The system can be fully closed, sucking fresh air in from outside the room, via a different inlet pipe or a balanced flue.

7) Use of negative pressure means that the system does not have to be completely airtight, whereas a leaky system would be a problem with positive pressure.

8) the use of an electric fan, to suck air through the system, means that the fire is instantly controllable and can be computer controlled, possibly using positive feedback to control the fire profile. A timer, proximity detector, or remote controller can turn down the fire when no-one is in the room. 9) a more powerful fan can be used to pull the exhaust gas through highly compressed filters, enabling more particulates to be removed from the gas. this can be done in the hot input of the heat exchanger, enabling secondary/tertiary burning, and in the cool output of the exchanger, enabling a washable micro-filter to be used to remove particles of a few microns.

10) the exhaust gas can be bubbled through wet scrubbers to remove very small particles and some of the carbon dioxide from the exhaust gas.

11) more effective particulate removal may enable greener wood to be used.

Figure 4 illustrates a schematic diagram of a further arrangement for a heat exchanger in use on an improved stove. The stove of Figure 4 is similar to the stove described previously in relation to figure 3C. The heat exchanger comprises a plurality of heating fins. An optional cooling fan is provided to urge air towards the cooling fins of the heat exchanger.

The heat exchanger and ventilation device are provided as an assembly that can be used to retrofit an existing stove installation by replacing a section of the original flue pipe. The heat exchanger and ventilation device may be coupled to an existing flue pipe installation.

Figure 5A illustrates a schematic diagram of a further arrangement for a heat exchanger in use on an improved stove. The assembly has an inlet manifold and an outlet manifold and a plurality of pipes extending between the inlet manifold and the outlet manifold providing heat exchange elements of the heat exchanger. A cooling fan may be arranged to urge air towards the heat exchange elements. In this way, the heat exchange assembly can provide a radiator for position within a room to be heated. Figure 5A also illustrates a schematic diagram of an example of a connector for retrofitting the heat exchanger onto the improved stove.

Figure 5B illustrates a close-up schematic diagram of the connector for retrofitting the heat exchanger onto the improved stove shown in Figure 5A. The connector may also be referred to as a "T" connector. The connector couples together an outlet of the stove, the inlet manifold, and a flue pipe, which may a pre-installed flue pipe. In this example, a first opening of the connector is coupled to an outlet of a combustion chamber of the stove. A second opening of the connector is coupled to the inlet manifold. A third opening of the connector is coupled to the existing flue pipe. The connector is arranged, in this example, such that the combustion chamber outlet, the inlet manifold, and the flue pipe are arranged in an approximate "T" shape. An optional damper is sited in the flue pipe, downstream of the third opening of the connector with respect to the flow of the exhaust gas. Accordingly, exhaust gas exiting the combustion chamber of the stove is in fluid communication with the inlet manifold via connector. Specifically, the exhaust gas travels from the combustion chamber to the inlet manifold via the first and second openings of the connector. When the damper is closed, the exhaust gas cannot exit into the flue pipe via the third opening in the connector.

Figures 6 and 7 illustrate views of an example of an improved stove as demonstrated in Experiment 1. This shows an open system, where air is sucked in through a fire from the local environment. In an open system, ambient air is drawn into the fire from the room. This air is replaced by cold air being drawn into the room through the doors and windows, thereby reducing the heating efficiency of the fire.

Smoke and heat from the fire rises into a "blind" flue (also referred to as a "blind" chimney), where it is sucked out, by a 5 Watt electric motor, through four heat resistant exhaust pipes, each 3 metres long. By the time the exhaust gas reaches the motor, nearly all the heat has been lost to the environment through the walls of the tubes, so a heat resistant motor is not needed (a 5 Watt bathroom extractor fan was used for this experiment).

The blind chimney is "blind" in the same sense as a "blind alley". The blind chimney may have an enclosed end from which exhaust gases are removed by another flue pipe. A blind chimney may have a window to allow the fire to be visible.

The "blind” flue got very hot, as did the first meter of each of the four pipes, releasing their heat into the environment. A separate fan could be used to blow cold air over the "blind" flue or these pipes to increase this heat transfer. The fan may be a Peltier effect fan. To improve the heat recovery from the "blind" flue, by way of radiation and/or convection, the "blind" flue may have a large height, width, or diameter, and/or comprise a corrugated surface or cooling fins fitted to the outside surface of the "blind" flue.

Stainless steel scouring pads and stainless steel wire wool can be inserted in these pipes to increase heat transfer, facilitate secondary/tertiary burning and filter out particulates.

A very fine washable and reusable micro particle filter (as used in Dyson® vacuum cleaners) can be used at the cold motor end to filter out very small particulates. A setup like this could save over 1000 Watts of heat, at the cost of 5 Watts of electricity. This 5 Watts could come from mains or a battery that is charged by wind power or solar panels. At the cost of increasing the power of the motor to 20 or 30 Watts, more efficient filtering could be used. The exhaust gas could be sucked through a bath of lime water to remove some of the carbon dioxide, or scrubbed in a fine shower of used bathwater, removing many of the particulates and some of the carbon dioxide, forming weak carbonic acid.

Figure 8 illustrates another example of an improved stove as demonstrated in Experiment 2 - a retro-fit in-line heat exchanger experiment. Here the exhaust gas is sucked through a stack of metal plates, which absorb heat from the exhaust gas and release it into the room. Filter material, such as Stainless Steel scourers and Stainless Steel wire wool can be stuffed into the flue column to assist heat loss, secondary/tertiary burning and particulate filtration.

Figures 9A and 9B illustrate schematic diagrams of a further arrangement for a heat exchanger in use on an improved stove. A closed circuit wood burning stove according to the present disclosure. In a "closed" system, air is directly drawn into the fire from outside the room through a pipe and exits the room through a pipe. There is, therefore, no direct fluid connection between the air in the room and the air in the stove. This leads to greater heating efficiency of the "closed" system.

The "Blind" flue can be raised, or hinged open, to feed and clean the fire (this mechanism is not shown). Also, if it is left in the slightly open position, the fire can be seen directly without any smoke escaping.

The fuel burning surface is relatively horizontal and a separate relatively vertical "blind" chimney superstructure that sits on the fuel burning surface, with a relatively air-tight seal between the two. The "blind" chimney is hinged, along one edge of the fuel burning surface, or able to be raised from, and lowered onto the fuel burning surface, using a raising mechanism with a heat resistant handle. The "blind" flue may be detachable, able to be lifted away from the fuel burning surface. Alternatively, a surface on which the fire burns may be lowered away from the "blind" chimney.

The fire is fed air from below, in a manner similar to a standard solid fuel burning stove, when the "blind” chimney is raised, the system temporarily being "open".

One or more flue pipes, opening relatively high up inside the "blind" chimney (even if the "blind" chimney is raised) sucking exhaust gas upwards from the fire into the chimney cavity, possibly through a secondary burning zone, then downwards through the pipes, either round or through the surface that supports the fire and entering the heat exchanger means outside the combustion chamber. Figures 10A and 1OB illustrate yet another example of an improved stove as demonstrated in Experiment 3. This shows an open system. Smoke and heat from the fire rises into a "blind" flue, where it is sucked out, by a electric motor, through four heat resistant exhaust pipes, each 3 metres long. In Experiment 3, the exhaust pipes rise up into a "blind" flue or chimney to act as an inlet for the exhaust gases. The pipes have stainless steel scourer I scrim I wire wool stuffed into their inlets to assist heat loss, secondary/tertiary burning and particulate filtration. The exhaust pipes extend down below the fire in a coiled configuration. The electric motor is connected to the outlet end of the pipe. By the time the exhaust gas reaches the motor, nearly all the heat has been lost to the environment through the walls of the tubes, so a heat resistant motor is not needed (a 5 Watt bathroom extractor fan was used for this experiment).

In Figure 10A, the "blind" flue/chimney is not fitted over the fire. This demonstrates that relatively little cooled flue exhaust gas is expelled from the exhaust extractor fan without the "blind" chimney fitted over the fire. In comparison, Figure 10B shows the same set up but with the "blind" chimney fitted over the fire. The "blind" chimney allows the pipe inlets to capture a greater proportion of the exhaust gases, thus more exhaust gas will flow through the pipe coils, more heat will be extracted from the hot exhaust gas, and thus more cooled exhaust gas can be seen coming out of the exhaust extractor fan.

In use, the "blind” chimney of Figure 10B got very hot, as did the heat exchange pipes, releasing heat into the environment. A separate fan could be used to blow cold air over the "blind" chimney or the pipes to increase this heat transfer. The fan may be a Peltier effect fan. To improve the heat recovery from the "blind" chimney, by way of radiation and/or convection, the "blind" chimney may have a large height, width, or diameter, and/or comprise a corrugated surface or cooling fins fitted to the outside surface of the "blind" chimney.

The amount of heat recovered from the "blind" chimney may be further increased by painting the flue black, thereby increasing black body radiation. The amount of heat recovered from the "blind" chimney may be further increased by fitting vertical or vertically angled fins to the outside surface of the "blind" chimney, thereby increasing heat induced updraft, possibly inducing spiral vortices. The effect of said fins is increasing heat loss to the surrounding environment by convection. Further, the "blind" chimney could be coupled to a heat sink, such as a thermally conductive surface, thereby increasing the conducted heat loss to the room. A domestic wood burning or solid fuel burning stove comprising the heat exchange assembly of any of the examples discussed above effectively replaces the role of the flue and emulates the "chimney effect", thereby eliminating the need for a chimney and any constraints associated with the "chimney effect". One advantage is being to enable hot gas, emanating from the fire, to be cooled to room temperature, or even below room temperature, with all the heat being recovered and put to useful purpose. Importantly, the process has no effect on the functionality or visual appearance of the fire.

The following key advantages are also disclosed: a/ the disclosures of the present application are particularly useful for domestic burners. b/ As most wood-burning stoves are used for psychological reasons and are often a secondary source of heating, i would like to emphasise the fact that the heat exchange assembly endeavours to maintain the sense of well-being wood burning stoves evoke, essentially looking the same as conventionally aspirated fires, with visible rising flames and smoke. Allowing the user to control the fire, maybe allowing it to smoulder some of the time, if that is what the user requires. Not necessarily trying to blast the living daylights out of it all the time. c/ the heat exchange assembly can be retro-fitted to existing stove designs, or be a custom design, eliminating the need for chimneys and flue liners, eventually expelling the flue gas through plastic pipes if required. This significantly cuts material and installation costs and site requirements. d/ the heat exchange assembly may be combined with devices and/or assemblies, as disclosed below, for clearing the flue gas by passing it through a second, possibly propane, butane or propane flame, or alternatively passing the flue pipe (possibly perforated) through the hottest part of the fire, thereby recovering more energy from the burnt smoke, soot, and volatiles, and potentially enabling the clear, carbon monoxide free smoke to be expelled from the premises at ground level. e/ it is possible to reclaim all of the heat from the flue gas, thereby reducing the amount of fuel required.

The following embodiments are also disclosed: A domestic Wood burning or solid fuel burning stove, where a heat exchanger, (or sequence of heat exchangers) is used to cool the flue gas to room temperature, plus or minus a few degrees Celsius e.g. + 40 / -20 degrees Celsius, while maintaining the relaxing appearance and ambiance of a normally aspirated wood-burning stove, at the same time preventing heat being wasted and recovering this heat for useful purposes - the process being facilitated by the normal flow of rising hot flue gas being replaced by means of a suction device sited after the heat exchanger(s).

The heat exchanger may comprise a ventilation device, which may also be referred to as a suction device, as disclosed above in relation to Figures 1-10. The suction device may be an electric fan. The suction device may be mechanical.

The smoke and volatile gases leaving the combustion chamber are burnt to remove smoke, soot, carbon monoxide and other volatile gasses, before entering the heat exchanger(s), resulting in the flue gas being smoke-free, and at the same time producing more energy from the fire, which is captured by the heat exchanger, thereby resulting in the stove being more than 100% efficient, and preventing any build-up of creosote or soot in the flue pipe or heat exchanger.

The flue pipe passes through or extremely close to the main fire, enabling the flue gas inside to be heated, ignited and burnt by the main fire.

The flue gas passes through, or extremely close to a second independent smokeless fire or electric device, where the flue gas is ignited and burnt.

The flue pipe, after the (last) heat exchanger, is plastic.

The cooled, flue gas is expelled through an existing chimney, a hole in the wall or directly to the atmosphere.

The device may be a retro-fit, fitted to an already established, or new solid fuel or woodburning stove.

The door may slide up and down, reducing the amount of smoke entering the room when the door is opened or closed.

The stove is may be a custom design, incorporating an internal flue that guides smoke, rising from the fire, downward and out the lower part of the stove. The power of the suction device may be controllable, enabling various functions during different phases of the fire, under the direct, or remote control of the operator or an electronic device.

The suction device can temporarily become a blowing device if required.

The stove can be fitted anywhere in a property, without the need for a chimney or flue liners.

The stove can be mobile, being movable from room to room or into the garden occasionally.

The parts outside the combustion chamber are easily accessible, low-cost, simple to maintain and readily replaceable.

Part of the heat exchanger consists of two concentric pipes, hot flue gas passing between the inner pipe and the outer pipe, creating a very hot outer pipe that readily radiates and convects heat.

The suction device is sited after the heat exchanger, ensuring the whole system before that is running at negative pressure, enabling the system to be slightly leaky without compromising safety.

The following discussion is also disclosed.

Q: Is it possible to prevent wood burning stoves being banned?

A: Yes.

There has been a lot of press and complaints recently, particularly in Scotland, about the banning of wood burning stoves due to their adverse environmental impact in terms of greenhouse gas production and smoke. The problem is exacerbated by the lack of efficiency of many of these stoves, some nearly losing half the heat up the flue. Open fires may waste 90%. Manufacturers are making great efforts to increase efficiency and reduce pollution but are they missing a trick?

Nottingham designer, Ron Binstead, decided to see if he could improve on existing designs and, to his surprise, he found a highly effective solution. As a result of a few experiments he managed to invent and has applied for a patent for a very low cost way anyone could modify their existing stove to recover all this lost heat, creating massive savings in the amount of wood required, with a proportionate reduction in carbon dioxide and soot. This method also slashed the potential costs of any new installations.

The present situation.

Traditionally, domestic stoves rely on rising hot flue gas to draw fresh air through the fire. Much effort is put into creating and maintaining a good "draw". If it doesn't draw properly, expensive heat resistant extractor fans may be installed at the top of chimneys to assist. Chimneys are lined with heatproof liners and are carefully designed so they do not impede the flow of flue gas. This can easily cost £1000 or more to install. To get a fire started, a chimney flue may need to be pre-heated. If reclaiming heat from the flue pipes, great care is taken not to reclaim too much in case the fire ceases to draw. As a result of meticulous planning, complicated design and complex operating procedures, expensive wood burning stoves can achieve an efficiency of 80% or more.

A low cost, more efficient alternative.

Being new to the technology, Ron took a fresh look at the problem, basing his approach on modern technology. His experiments led him to the conclusion that much wood burning stove technology may be counter productive and unnecessary.

An aim of his experiments was to retain the relaxing, comforting and heating features of a traditional wood burning stove, but significantly improve efficiency, reduce emissions and costs (if possible) and simplify installation and maintenance.

He started by using a very efficient heat exchanger to extract substantially ALL the useful heat from the flue gas, and use ALL this heat to warm the room. A heresy according to trade norms, but this proved pivotal to solving the problem. The inevitable consequence was to destroy the flue gas's ability to rise up the flue, blocking any more air from being drawn through the fire. However, Ron found that a small bathroom extractor fan solved the problem, sucking the gas out of the flue. Because the flue gas was cold after passing through the heat exchanger, a heat resistant fan was not needed; neither was a heat resistant flue liner; or even a chimney. The cold flue gas could just be sent to the outside of the house through a thin plastic pipe, via a small hole in the wall, or it could be sent up the inside of the existing chimney.

Other advantages of using an extractor fan: a) it creates a slightly reduced pressure inside the system, meaning that slightly leaking joints were not a problem. In that respect it was more fail-safe than existing systems which create positive pressure. b) it also creates a strong air flow in the system from the very start, so fires start up very quickly. This significantly reduces the amount of smoke produced at start-up - a phase when much smoke is produced. c) the flue gas is under the operators control and can be sent through a variety of pollution controlling treatments. d) the fire can be controlled remotely, by Bluetooth or some other means, meaning it can be completely under software control; e.g. the fire can be turned on or off by a phone app., suction can be increased when the stove door is opened, thereby reducing the amount of smoke that gets into the room; the fire could automatically shut-down if too much smoke is produced.

Other advantages of extracting all the heat:

Flue gas contains a significant amount of water vapour that is produced by heating moisture in the wood, and as a bye-product of burning the wood. Cooling the flue gas causes this water vapour to condense and release its latent heat into the room. This extra heat enables a wood burning stove to be even more efficient.

A working example.

Figure 11A illustrates yet another example of an improved stove. Figure llB shows a rear view of the same stove as Figure 11A. The picture shows one of many retro-fit heat exchange systems, designed by the author, seated on top of a traditional 5 Kilowatt wood burning stove. Air is drawn through the apparatus by a 5 Watt plastic mixed flow bathroom extractor fan. Heat from the fire is "sucked" into the heat exchanger, where it loses most of its heat, by radiation and convection, into the room. In this way, about 1 kilowatt of heat is recovered for just 5 Watts of electricity. This electricity may come from a range of sources, such as the mains or a solar charged battery. At the bottom of the downpipe pipe, the flue gas is cool enough for metal pipework to be replaced by plastic. The plastic pipe shown is a standard 40mm kitchen sink wase pipe, 3 metres long. Alternatively, the plastic pipe shown may be a standard 40mm kitchen sink wase pipe, 6 metres long. A much longer pipe will need a slightly more powerful extractor fan.

The Heat exchanger in Figs 11A and 11 B may be made super-efficient by the hot gas being channelled between an outer 6" flue pipe and a blocked inner 5" flue pipe, the flue gas having to travel in the Vi" gap between the two. This leads to a super-hot outer skin that radiates heat very quickly. That is why the flue part loses so much heat with just a 33cm length, in this example. The same process can be applied to other parts of the heat exchanger. In a final product, the heat exchanger may be surrounded with a mesh framework to prevent people burning themselves.

This design eliminates the need for heat resistant flue liners, chimneys, chimney sweeping, and specially constructed fireplaces, and enables stoves to be mobile, possibly being movable from room to room or outdoors, as required. It, therefore, sets installing a wood burning stove more on a par with installing a washing machine rather than a significant house rebuild, saving thousands of pounds in material, installation and maintenance costs, at the same time significantly improving fuel efficiency.

Although this method already reduces the amount of smoke produced; for example - good fire hygiene, such as starting a fire with an eco-fi relighter nested on top of the fire instead of underneath it; similarly, adding new material under the existing hot fire instead of on top. Both these methods reduce the amount of smoke produced in the first place. Another method is feeding the smoke back through the fire and burning it, thereby gaining more energy from the wood.

Apart from the cost of the original stove, the whole ancillary system could be assembled for about £100. The system is readily dismantled for cleaning, or parts can be recycled and replaced with new parts.

These experiments show that it is possible to take a new look at problem technologies and come up with usable, non-problematic solutions.

Hopefully the adoption of this sort of technology might increase the take-up of wood burning stoves and help prevent further bans being introduced.

Removing smoke from the flue

A further aspect of the disclosure relates to a smoke reduction device for a stove. The smoke reduction device is intended for domestic stoves, such as wood burning stoves, and can be fitted to an existing stove as a retrofitted modification or provided in a new stove installation. However, smoke reduction devices according to some examples have been found to be very efficient at removing smoke and they may also find applications in nondomestic stoves, for example those with a higher power output than that described previously, which may be used in commercial or industrial settings. Further, the smoke reduction device may be used in combination with or separately from the heat exchange assembly described in relation to the previous examples.

The smoke reduction device is intended to be used to remove smoke produced by a solid fuel burning stove.

Smoke is composed of a range of volatile and non-volatile gases and particles in a wide range of sizes.

The volatile gases are produced when the fire is not hot enough to ignite them.

The non-volatile gases consist mainly of nitrogen, oxygen, carbon dioxide, Water vapour and Carbon monoxide, all of which are colourless and clear.

The visible part of smoke is mainly composed of small particles of carbon and unburnt and partially burnt wood particles, the remainder being a small amount of chemical ash. The most dangerous constituents health-wise are carbon monoxide and the particulates.

These particles, many of the volatile gases and the carbon monoxide can be burnt by passing the smoke through a flame or a source of heat. This creates clear carbon dioxide, water vapour and some extra heat.

The resulting clear non-toxic flue gas being a mixture of nitrogen, oxygen, carbon dioxide and water vapour.

The carbon monoxide is burnt to carbon dioxide and water, as are the other volatile gases.

Figure 12A illustrates a schematic diagram of a smoke reduction device 1200, which may also be referred to as a smoke removal device. The smoke reduction device 1200 comprises an inlet 1202 configured to receive exhaust fluid from a stove (not shown) and an outlet 1204 for expelling exhaust fluid from the smoke reduction device 1200. A housing that defines the inlet 1202 and outlet 1204 of the smoke reduction device 1200 may be provided by or integrally formed with a flue of the stove. The smoke reduction device 1200 defines a passage between the inlet 1202 and the outlet 1204 for the passage of exhaust fluid 1206 from the stove. A heat source 1208 of the smoke reduction device 1200 is provided within the housing. The heat source 1208 is provided between the inlet 1202 and the outlet 1204 and arranged to burn at least some of the exhaust fluid and smoke from the stove so that the smoke content expelled from the outlet 1204 is reduced compared to the smoke content of the fluid received at the inlet 1202. The heat source 1208 may be provided by a burner that provides a flame 1210 to cause the at least partial combustion of the fluid 1206 flowing between the inlet 1202 and outlet 1204 of the device 1200.

Figure 12B illustrates an example of a smoke reduction device with its housing removed. In this example, the heat source is provided by a burner that produces a flame to combust the fluid received from the stove.

It will be appreciated that the smoke reduction device 1200 may be provided by or attached to a stove for burning solid fuel. Such a stove has a combustion chamber and the device inlet 1202 of the smoke reduction device 1200 is provided in fluid communication with the combustion chamber to receive exhaust gas and smoke from the combustion chamber. The heat source 1208 in the smoke reduction device 1200 can be considered to be a secondary heat source with respect to the primary heat source of the stove. In such examples, burning is brought about by using two layers of fire or heat; for example a lower, basic fire and an upper smokeless source of heat between the main fire and the flue.

The upper source of heat creates an updraft that naturally draws the smoke through it. This updraft may be increased when using a fan to draw air through the system as described with reference to earlier embodiments.

Most smoke is produced at the start of a fire, whereas very little smoke is produced when the fire is fully underway. Once the fire becomes substantially smokeless, the upper source of heat can be turned off or allowed to go out.

This upper source of heat could be provided by:

- A small smokeless solid fuel fire, a gas or liquid burner, or an electric heating element between the main fire and the flue.

- The smokeless solid fuel could be red hot "coals" in a wire basket.

When the main fire is hot and has reached the smokeless stage, some of the main fire can be transferred to the upper fire, if new material that is a potential source of smoke, is to be put on the main fire.

The smoke reduction device 1200 may further comprise a controller (not shown) configured to control operation of the heat source 1208 in accordance with a level of smoke that it likely to be produced by the fire. The level of smoke may be measured directly using a smoke detector or may be determined or estimated based on another property of the system, such as the temperature, the light level, or the amount of time that has passed since a fire was started in the stove. A sensor, such as a light or temperature sensor, may be provided in the stove, for example in the combustion chamber of the stove, the flue or the smoke reduction device 1200 in order to measure a property at the location of the sensor. The controller may be configured to stop the generation of heat by the heat source 1208 in response to the level or smoke or a related property such as the temperature, light level of elapsed time reaching or exceeding a threshold.

Figure 13 illustrates a stove with possible positions for placement of a smoke reduction device along an exhaust path provided by a flue. The stove optionally is provided with a heat exchanger and fan which may be provided in the form as described with reference to the previous examples. The smoke reduction device may be provided downstream from the fan in line with the flue (position A). Alternatively, the smoke reduction device may be provided upstream from the fan, nearer to the stove than the fan. The smoke reduction device may be provided between the fan and the heat exchanger (position B). In this example (position B), the smoke reduction device is provided downstream from the heat exchanger. Alternatively, the smoke reduction device may be provided upstream from the heat exchanger. Position C illustrates a smoke reduction device that is provided in line with the flue, upstream from the heat exchanger and downstream from the combustion chamber of the stove. Alternatively, the smoke reduction device may be provided within the combustion chamber of the stove. However, in all cases, the smoke reduction device must provide a secondary form of burning so that it can combust the smoke products from the primary form of burning. In position D, the smoke reduction device is substantially above the primary combustion within the combustion chamber and in example E the smoke reduction device is within the primary site of combustion in the combustion chamber.

With reference to Figure 13:

Position A: is at the exit of the flue. This wastes all the secondary heat from the burning process, both from the material used to burn the smoke and from the burnt smoke particles, volatiles and carbon monoxide. Soot and volatiles accumulate throughout the system.

Position B: this would send very hot gas through the extractor fan and waste all the secondary heat. Soot accumulates between the fire and this burner, but is prevented from affecting the extractor fan.

Position C: this sends both primary and secondary heat through the heat exchanger where it is recovered and used to heat the room. It is in a convenient position for a retro-fit, with easy access when adjustments, like topping up fuel, are required. Soot and volatiles accumulate within the combustion chamber, but are prevented from accumulating in the heat exchanger, the extractor fan and the flue.

Position D: this sends both primary and secondary heat through the heat exchanger where it is recovered and used to heat the room. The stove door would possibly need to be opened when refuelling is required. Soot and volatiles are prevented from accumulating in the heat exchanger, the extractor fan and the flue.

Position E: this sends both primary and secondary heat through the heat exchanger where it is recovered and used to heat the room. It is conveniently positioned when topping up the secondary fuel, but would impact the main fire visually. Soot and volatiles are prevented from accumulating in the heat exchanger, the extractor fan and the flue.

The optimal positions are C and D.

Figure 14A illustrates smoke at the outlet of a stove with a smoke reduction device that is inactive. Figure 14B illustrates a reduced level of smoke compared to Figure 14A at the outlet of the stove with the smoke reduction device when the smoke reduction device is active.

The disclosure also relates to a method of operating a stove having a smoke reduction device. The method allows smoke emissions to be reduced. In a general form, the method of operating the stove includes activating the heat source of the smoke reduction device and subsequently lighting a fire in the stove. Subsequently, the heat source of the smoke reduction device can be deactivated, for example in response to a temperature exceeding a temperature threshold as discussed above with respect to the optional controller of the device, although this can also be performed manually.

According to one example, a method of operating the stove includes a process of starting a smokeless (or reduced smoke) fire:

1. Lay the main fire but do not light it yet.

2. light the top smokeless fire or turn on its source of heat.

3. turn on the extractor fan to suck air through the system.

4. Light the bottom fire, possibly with fire-lighters.

5 Close the stove door.

6. If the upper fire runs out of fuel before the main fire is smokeless, refuel the upper fire.

6. Let the main fire burn until it is smokeless.

7. Turn off the upper fire, or let it run out of fuel.

8. If more, potentially smoke generating fuel is to be added to the main fire, turn on the upper fire, or transfer some of the hot "coals" from the main fire to the upper fire. 8a. If more, potentially smoke generating fuel is to be added to the main fire, feed the fresh material under the hot fire, possibly in the ash can and leave for about some time. During this time the fresh material will dry out and possibly start releasing smoke. This will rise through the hot fire above it and get burnt, thereby destroying the smoke.

9. Add the new fuel to the lower fire.

9a. After this time, or longer, the fresh partially dried material can, a) either be placed on top of the hot fire, where hopefully it will burn without smoke, or better b) be lifted up to, and in direct contact with the hot fire above it.

The use of method b) ensures that any smoke released will be burnt away. Process b) can be repeated.

10. Close the stove door.

Advantages of burning the flue gas at positions C or D include: recovering heat from the main fire and the smoke reduction device, while reducing soot in the heat exchanger, extractor fan and exhaust channel. Position A has none of these advantages. One disadvantage of using a second source of heat to burn the flue gas is the cost of the extra fuel used. However, this disadvantage is mitigated by the fact that the heat from burning this fuel, and the extra heat from burning the volatiles, carbon monoxide and particulates is not wasted up the flue if positions C, D or E are used, as it is captured and returned to the room by the heat exchanger. By contrast, all this heat is wasted if positions A or B are used.

Advantages of burning the flue gas, in particular the advantages of burning the flue gas at positions C or D as illustrated in Figure 13, include -

1. Extra heat is extracted from burning the smoke particles and carbon monoxide, as well as from the fuel needed to burn the smoke.

2. Having removed the smoke, at source, there is no soot or other chemicals to clog up the heat exchanger or exhaust pipes, thereby reducing maintenance requirements.

3. As the cool, clear flue gas is non-toxic, it can be sent via plastic pipes through an outside wall directly to the outside atmosphere.

4. The wood burning stove has minimal environmental impact in terms of smoke particulates and carbon monoxide. 5. Potentially green/wet wood can be burnt, reducing the requirement for kiln dried or seasoned wood.

Figure 15A illustrates a schematic diagram of a smoke reduction assembly 1500a, which may also be referred to as a smoke removal assembly, configured with a combustion chamber 1502a of a stove (not shown). The smoke reduction assembly 1500a comprises an assembly inlet 1504a configured to receive exhaust fluid containing smoke from the stove and an assembly outlet 1506a for expelling exhaust fluid from the assembly 1500a. The smoke reduction assembly 1500a defines a passage between the inlet 1504a and the outlet 1506a for the passage of exhaust fluid 1506a from the stove. The inlet 1504a, outlet 1506a and passage are defined by a conduit. In this example, the conduit is a flue pipe 1508a.

A heat source is provided within the combustion chamber 1502a when the stove is in use. The heat source may be provided by a solid-fuel-burning fire. In this example, the heat source is provided by a wood-burning fire 1510a sitting atop a fire grate. The flue pipe 1508a is arranged such that at least an intermediate section 1512a of the flue pipe 1508a is situated proximate the wood-burning fire 1510a when the stove is in use. The exhaust fluid is collected by the inlet 1504a from above the wood-burning fire 1510a, and the conduit 1508a passes through or proximate the hottest part of the wood-burning fire 1510a, where the exhaust gas is heated and particulates in the exhaust gas will ignite if sufficient air is available.

The intermediate section 1512a of the flue pipe 1508a, that is the section that is proximate the wood-burning fire 1510a when the combustion chamber is in use, may comprise one or more ignition features. In this example, the intermediate section 1512a of the flue pipe 1508a comprises one or more openings 1514a. The openings 1514a may be one or more holes, slits, or perforations in the flue pipe 1508a. The openings 1514a cause the suction of hot gas and/or flames from the wood-burning fire 1510a into the flue pipe 1508a. In practice, the openings may be sized and configured such that 10% of flaming gas is sucked through the openings 1514a while the remaining 90% gas is sucked into the inlet 1504a above the fire.

The intermediate section 1512a of the flue pipe 1508a may be any one of: above the fire, below the fire, or adjacent the fire. The openings 1514a may be positioned just above the part of the fire that is likely to become hottest during use, so as not to suck in ash. In the example illustrated in figure 15A, the openings 1514a are positioned below the woodburning fire 1510a, so the openings 1514a further cause suction of red-hot ash from the wood-burning fire into the flue pipe 1508a. The suction of the hot gas, flames, and/or hot ash from the wood-burning fire 1510a into the conduit 1508a causes ignition of at least some of the smoke particles in the exhaust fluid so that the smoke content of the exhaust fluid expelled from the assembly outlet 1506a is reduced. The suction of hot ash from the fire 1510a provides the further advantage of vacuuming up the ash, thereby preventing its build-up in the fire grate. In some examples, the smoke reduction assembly further comprises a filter for trapping ash. The filter may be positioned anywhere between the openings 1514a and the smoke reduction assembly outlet 1506c.

Figure 15B illustrates an alternative arrangement of a smoke reduction assembly 1500b that is generally similar to that described previously with reference to Figure 15A. In the embodiment of Figure 15B, the exhaust gas flows into the inlet 1504b which is situated above the fire, through a section of the flue pipe 1508b that extends outside of the combustion chamber 1502b and downwards, then through another section of the flue pipe 1508b that extends back into the combustion chamber 1502b below the wood-burning fire 1510b, and then flows through the intermediate section 1512b of the flue pipe 1508b that is proximate the wood-burning fire 1510b and comprises the openings 1514b.

Before the exhaust gas containing smoke gets to the perforated section of the flue pipe 1508b, a percentage of fresh air could be mixed with it, thereby ensuring good combustion of the flue/exhaust gas in the flue pipe 1508b. The amount of air could be regulated by an adjustable mechanism. In the examples shown in Figures 15A-B, the flue pipe 1508b comprises an adjustable flue control for introducing fresh air into the exhaust gas.

Figure 15C illustrates another embodiment of a smoke reduction assembly 1500c generally similar to that described previously with reference to Figure 15A. In this embodiment, the flue pipe 1508c inlet 1504c is positioned inside the combustion chamber, which may also be referred to as a fire box, above the fire. The flue pipe 1508c then runs through the hottest part of the fire 1510c and expels exhaust gas out of the outlet 1506c. Therefore, exhaust gas is collected from above the fire, and passes through the hottest part of the fire, where it is heated to red heat (up to 600 degrees Celsius) by the wood-burning fire 1510c. Wood particles spontaneously ignite about 300 degrees Celsius, Creosote about 250 degrees Celsius and Carbon (soot) ignites between 300 degrees Celsius and 450 degrees Celsius. Therefore, at the temperatures reached inside the intermediate section 1512 of the flue pipe 1508c proximate the wood-burning fire 1510c, the particulates will all ignite if sufficient air is available. The intermediate section of the flue pipe 1508c that is proximate the wood-burning fire 1510c comprises one or more baffles 1516c, instead of openings, arranged within the flue pi pe 1508c. The baffles 1516c are configured to transfer at least some of the heat from the heat source within the combustion chamber, or firebox, 1502c to at least some of the smoke in the exhaust fluid in the flue pipe 1508c to facilitate ignition of the at least some of the smoke. The baffles 1516c may cause ignition of any volatiles, soot and other smoke particles, converting them to carbon dioxide and water. Burning wood particles will ignite carbon monoxide. This results in exhaust gas that is carbon monoxide and smoke-free. In a preferred embodiment, the baffles 1516c are made of a thermally conductive material. As discussed previously, the hot exhaust gas should spontaneously ignite when the temperature of the baffles 1516c is hot enough. If spontaneous ignition does not occur, an automatic sparking system may be incorporated into the flue pipe 1508c. This would ignite any volatile gases and carbon monoxide. For example, a sparking plug could be used.

Before the exhaust gas containing smoke gets to the baffles 1516c in the flue pipe, a percentage of fresh air could be mixed with it, thereby ensuring good combustion of the flue gas in the pipe. The amount of air could be regulated by an adjustable mechanism. In the example shown in Figures 15C, the flue pipe 1508c comprises a secondary air input and adjustable air control for introducing fresh air into the exhaust gas.

Figure 15D illustrates an alternative flue input 1520. An inlet 1522 of the alternative flue input 1520 may replace the inlet of the smoke reduction assembly discussed above with reference to Figures 15A-C. Alternatively, the alternative flue input 1520 may be retrofit to an inlet 1508a, 1508b, 1508c of an existing flue pipe generally similar to that described previously with reference to Figures 15A-C such that the inlet 1522 of the alternative flue input 1520 is in fluid communication with the inlet 1508a, 1508b, 1508c of the flue pipe.

In this example, a firelighter is provided at the inlet 1522 of the alternative flue input 1520. The firelighter 1522 may be ignited at the inlet 1522 when a new fire in the stove is about to be lit - the smokiest time for a fire is at its beginning. The firelighter 1522 should burn for approximately the first 10 minutes - long enough for the main fire to get underway. If approximately 10 minutes is not long enough, another firelighter 1522 can be used. When the main fire has reached full heat, extra firelighters should no longer be necessary. Smoke will be drawn past the burning firelighter 1524 into the flue pipe via the inlet 1522. As it passes the firelighter 1524, the smoke will be burnt by the firelighter flames, forming smokeless flue gas. In other examples, a smokeless log may be ignited and burned at the inlet 1522 of the alternative flue input 1520 instead of a firelighter. Figure 15E illustrates a possible retro-fit for a smokeless stove with the smoke reduction assembly 1500e, similar to the smoke reduction device described previously with reference to Figures 15C-15D, fitted internally. A smoke reduction device similar to the smoke reduction device described previously with reference to Figures 15A-15B could be retrofitted in a similar manner. The retro-fitting would involve drilling a plurality of holes in the sides of the stove to accommodate the smoke reduction assembly 1500d. In this example, 4 holes are drilled into the stove.

Various methods of operation (a) - (d), which may be implemented using the assembly described with reference to Figures 15A-E, are also disclosed:

(a) Continuous burning.

The technique is particularly suited to larger wood-burning stoves that are permanently left burning. The flue pipe, running through the hottest part of the fire, will already be red- hot. Fresh smoke generating material can be placed on top of the fire where it starts to burn and create smoke. This smoke is sucked through the red-hot pipe where it is burnt and cleared of smoke (as described above).

(b) Starting a new fire with a gas poker.

Figure 15C shows a situation where the fire can be started from cold. Before adding any burnable material, the secondary air control valve is opened, the extractor fan is turned on and the gas poker (sited under the flue pipe in the grate) is lit. When the flue pipe is red-hot some burnable material is placed around the hot part of the flue pipe. This will generate some smoke that will be cleared when it is sucked through the hot flue pipe section. More material can then be added until a hot bed of burning embers surrounds the flue pipe.

The gas poker can then be turned off, as the hot burning material will be sufficient to keep the flue pipe hot enough to burn any further smoke. Fresh burnable material can be added without further need for the gas poker.

(c) Starting a new fire with hot embers from another fire.

Hot embers can be transferred from another fire and placed around the flue section in the grate, thereby heating the pipe to red-heat. Once the flue is hot enough, fresh smoke generating burnable material can be placed on the fire.

(d) Starting a new smoke-free fire with fire-lighters. The initial fire is started with smokeless material, using smokeless fire lighters. Once a body of hot embers is sufficient to heat the flue pipe to red-heat, fresh smoke generating burnable material can be added to the fire.

A stove comprising a combustion chamber configured with the smoke reduction assembly as described above with reference to Figures 15A-E is optionally provided with a heat exchanger and ventilation device, such as a fan, which may be provided in the form as described with reference to the previous examples. The flue gas can be cooled below room temperature, possibly with water or even a heat pump.

Figure 15F illustrates an example of a stove comprising a combustion chamber 1502f configured with the smoke reduction assembly 1500f similar to the smoke reduction assembly as described above with reference to Figures 15A-E, a heat exchange assembly 1530f, and a ventilation device, which in this example is an extractor fan 1532f. The stove, heat exchange assembly 1530f and extractor fan 1532f may be provided similarly as discussed previously with reference to the examples in Figures 1-11 and 13. The combustion chamber only requires three holes to be drilled into it, in this example. A first hole accommodates the assembly outlet. A second hole accommodates the secondary air input. A third hole, which is optional, accommodates the optional gas poker.

In this example, the assembly outlet 1506f of the smoke reduction assembly 1500f is coupled to an inlet 1534f of the heat exchange assembly 1530f via an ash trap 1507f. The ash trap comprises a baffle for blocking ash and a reservoir below the baffle for collecting fallen ash. The reservoir may be removable or serviceable. Providing an ash trap upstream of the portion of the first heat exchange conduit 1538f comprising baffles 1539f can reduce the maintenance demands on the first heat exchange conduit 1538f. Accordingly, the exhaust gas from the combustion chamber 1502f of the stove travels through the smoke reduction assembly 1500f, at least some of the smoke is burned from the exhaust gas, and the exhaust gas with reduced smoke travels through the outlet 1506f of the smoke reduction assembly to the inlet 1534f of the heat exchange assembly 1530f. An outlet 1536f of the heat exchange assembly 1530f is coupled to an inlet of the extractor fan 1532f.

Between the inlet 1534f and outlet 1536f of the heat change assembly 1530f, the heat exchange assembly 1530f comprises one or more heat exchange elements configured to extract heat for external use from the exhaust gas and form cooled exhaust gas, as described previously with reference to other examples in the present disclosure. In this example, the heat exchange assembly 1530f comprises a first heat exchange conduit 1538f comprising baffles 1539f, one or more metal condensing pipes 1540f, and a second heat exchange conduit 1542f configured to collect the condensate. The exhaust gas travels from the inlet 1534f of the heat exchange assembly 1530f into the first heat exchange conduit 1538f, subsequently into the metal condensing pipes 1540f, and subsequently into the second heat exchange conduit 1542f. The heat exchange assembly may be configured to cool the exhaust gas down to one of: less than 60 degrees centigrade, approximately room temperature, and below room temperature.

The outlet of the heat exchange assembly 1530f is coupled to a plastic flue pipe 1544f. Said flue pipe can be made of plastic because the exhaust gas is cooled to a sufficient extent by the heat exchange assembly 1530f such that the plastic pipe will not be subjected to temperatures that would distort or melt the plastic. The extractor fan is coupled to the plastic pipe, downstream of the heat exchange assembly and the smoke reduction assembly. Accordingly, a negative pressure is generated up to the extractor fan, i.e. in the smoke reduction assembly, the heat exchanger, and associated pipework linking the two. The negative pressure forces, sucks, and/or propels the exhaust gas through the entire system depicted in Figure 15F.

Figures 15A-B show that ash could be sucked through the flue pipes, thereby helping keep the ash from clogging up the fire. Occasionally, the flow of gas facilitated by the fan could be reversed (i.e. blow instead of suck), for a fraction of a second or more, thereby breaking up and "gassifying" any ash deposits. The amount of suction could be boosted now and then to ensure all ash is cleared from the grate. An ash trap could catch this before the flue gas enters the heat exchanger. This will help clear out the ash when the gas flow reverts to normal "extraction" mode. This does not necessarily need the fan motor to be reversed. A simple in-line flow-reversal valve could be used instead.

A smoke reduction assembly as described above in relation to Figures 15A-F may be used separately from or in combination with the smoke reduction device described above in relation to Figures 12A-12B, and/or the stove arrangement as described above in relation to Figure 13.

Fluid flow reversal mechanism

Figures 16A and 16B illustrate a gas-flow reversal mechanism 1600 for a flue pipe. The gas-flow reversal mechanism 1600 has a first fluid port 1602 for coupling to a first portion the flue pipe and a second fluid port 1604 for coupling to a second portion the flue pipe or expelling exhaust gases directly into the environment. The gas flow reversal mechanism 1600 further comprises a fan conduit 1620, a first auxiliary conduit 1612 and a second auxiliary conduit 1614. The fan conduit 1620, the first auxiliary conduit 1612 and the second auxiliary conduit 1614 all branch between a first node 1622 and a second node 1624. The first fluid port 1602 is coupled to the fan conduit 1620, the first auxiliary conduit 1612 and the second auxiliary conduit via the first node 1622. The second fluid port 1604 is coupled to fan conduit 1620, the first auxiliary conduit 1612 and the second auxiliary conduit via the second node 1624.

The gas-flow reversal mechanism 1600 comprises a motorised fan 1606, or other means of propulsion, between the first fluid port 1602 and the second fluid port 1604. The fan 1606 has a fan inlet 1608 and a fan outlet 1610. The fan 1606 is disposed in line with the fan conduit 1620 between the first node 1622 and the second node 1624 so that the fan inlet 1608 is directly coupled to the first node 1622 and the fan outlet 1610 is directly coupled to the second node 1624. The fan 1606 is operable in a first direction which causes fluid to flow from the fan inlet 1608 to the fan outlet 1610.

A first valve 1616 is disposed at the first node 1622 and a second valve 1618 is disposed at the second node 1624. The first valve 1616 and the second valve 1618 are operable together in either a first configuration or second configuration.

In the first configuration, illustrated in Figure 16A, the first valve 1616 allows fluid communication between the first fluid port 1602 and the fan conduit 1620 and the first valve 1616 blocks fluid communication between the first auxiliary conduit 1612 and the fan inlet 1608. In the first configuration, the second valve 1618 allows fluid communication between the second fluid port 1604 and the fan conduit 1620 and blocks fluid communication between the second auxiliary conduit 1614 and the fan outlet 1610.

In the first configuration of the gas-flow reversal mechanism, the valves are configuration such that the motorised fan 1606 draws fluid to the fan inlet 1608 from the first fluid port 1602 via the fan conduit 1620 and the fan forces fluid from the fan outlet 1610 to the second fluid port 1604 via the fan conduit 1620.

In the second configuration, illustrated in Figure 16B, the first valve 1616 blocks fluid communication between the first fluid port 1602 and both of the fan conduit 1620 and the first auxiliary conduit 1612 and allows fluid communication between the first auxiliary conduit 1612 and the fan inlet 1608 via the fan conduit 1620. In the second configuration, the second valve 1618 blocks fluid communication between the second fluid port 1604 and both of the fan conduit 1620 and the second auxiliary conduit 1614 and allows fluid communication between the second auxiliary conduit 1614 and the fan outlet 1610 via the fan conduit 1620.

In the second configuration of the gas-flow reversal mechanism, the valves are configuration such that the motorised fan 1606 draws fluid from the second fluid port 1604 to the fan inlet 1608 via the first auxiliary conduit 1612 and forces fluid from the fan outlet 1610 to the first fluid port 1602 via the second auxiliary conduit 1614.

In the example shown in Figure 16, the first valve 1616 is hinged at a point where the first fluid port 1602 couples to the first auxiliary conduit 1612. In the first valve configuration, the first valve 1616 is in a first position that blocks an opening of the first auxiliary conduit 1612 at the first node 1622. In the second valve configuration, the first valve 1616 rotates about the hinge into a second position in which the first auxiliary conduit 1612 is in fluid communication with the fan inlet 1608 via the fan conduit 1620 and the first fluid port 1602 is in fluid communication with the second auxiliary conduit 1614. The second valve 1618 is hinged at a point where the second fluid port 1604 couples to the second auxiliary conduit 1614. In the first valve configuration, the second valve 1618 is in a first position that blocks an opening of the second auxiliary conduit 1614 at the second node 1624. In the second valve configuration, the second valve 1618 rotates about the hinge into a second position in which the second auxiliary conduit 1614 is in fluid communication with the fan outlet 1610 via the fan conduit 1620 and the second fluid port 1604 is in fluid communication with the first auxiliary conduit 161.

As described above, the pair of valves are operable together to alter a flow path within the mechanism, thereby allowing "reversal" of the gas flow without reversing the fan motor. An advantage of the gas-flow reversal mechanism 1600, as opposed to merely changing the direction of the fan, is that the use of the valves allows a very rapid, sharp reversed blast of air - possibly for less than a second. Disadvantages of merely changing the direction of the fan include that it is quite a slow process as it involves the fan stopping, starting it in reverse, stopping again and starting forward, this process could take 10 seconds or more for a PWM fan. This could stir up so much ash in the fire box that it could start coming out into the room. Also, all this ash could settle on, and smother the burning fuel.

In this example, the first valve 1616 is hinged around a point between the first end of the first auxiliary conduit 1612 and the first fluid port 1602, and the second valve 1618 is hinged at a point between the second end of the second auxiliary conduit 1614 and the second fluid port 1604. A smoke reduction assembly generally similar to that described previously with reference to Figures 15A-15D is optionally provided with the gas-flow reversal mechanism 1600. For example, the first fluid port 1602 of the gas flow reversal mechanism 1600 may be provided in fluid communication with the smoke reduction assembly outlet 1506b. Accordingly, the gas-flow reversal mechanism may switch rapidly to the second configuration to provide a very rapid, sharp reversed blast of air so as to break up and "gassify" any ash deposits and subsequently switch back to the first configuration to ensure all ash is cleared from the grate.

A heat exchange assembly for a solid fuel-burning stove as described above in relation to previously Figures is optionally provided with the gas-flow reversal mechanism in place of the ventilation device. The motorised fan of the gas-flow reversal mechanism provides the ventilation and/or suction means and advantageously provides the option of reversing the flow for, for example, breaking up ash deposits in the grate of the stove as discussed above.

Retro-fit stove

Figure 17A illustrates a retrofit or custom solid fuel-burning stove 1700 similar to the stove described previously with reference to Figures 11A and 11B. The stove comprises a combustion chamber 1702 containing a heat source 1704, which may be provided by burning wood. The combustion chamber 1702 comprises an air inlet 1706 and an outlet for expelling exhaust gas. The stove further comprises a heat exchange assembly 1708.

In this example, the combustion chamber 1702 is an existing combustion chamber that had already been installed and the heat exchange assembly 1708 has been retrofitted to the combustion chamber.

A first stage of the heat exchange assembly 1708 is provided by a first heat exchanger defined by a flue pipe comprising an outer flue pipe 1710 and an "blocked" inner flue pipe 1712. An inlet of the outer flue pipe 1710 is in fluid communication with the combustion chamber 1702. An inlet of the inner flue pipe 1712 is open and may be in fluid communication with the combustion chamber. An outlet of the inner flue pipe 1712 is "blocked" or "closed". The inner flue pipe 1712 is concentric within the outer flue pipe 1710. Accordingly, exhaust gas from the combustion chamber 1702 may travel up through the outer flue pipe 1710, around the inner flue pipe 1712. By forcing the exhaust gas to travel through the outer flue pipe 1710 and around the inner flue pipe 1712, a greater amount of the exhaust gas is in closer contact with the surface of the outer flue pipe 1710. Therefore, a greater amount of heat can be dissipated from the exhaust gas as it travels through the outer flue pipe 1710.

The outlet of the combustion chamber or inlet of the flue pipe is optionally provided with a smoke reduction device 1714, such as that described previously with reference to Figures 12-14, for example.

The inlet of the heat exchange assembly, defined by the inlet of the flue pipe, and the inlet of the smoke reduction device are both in fluid communication with the combustion chamber 1702 to receive the exhaust fluid from the combustion chamber 1702. The heat exchange assembly 1708 is arranged to receive exhaust fluid that has passed through the smoke reduction device 1714.

The heat exchange assembly 1708 further comprises a second stage comprising an inlet in fluid communication with the outlet of the outer flue pipe 1710. The second stage comprises a second heat exchanger 1716. A plurality of baffles 1718 are arranged within the second heat exchanger 1716 to facilitate transfer of heat from the exhaust gas.

Whereas the first heat exchanger defines a generally vertical fluid flow path in which exhaust fluid may rise, the second heat exchanger 1716 extends horizontally to define a lateral fluid flow path between the baffles 1718.

The heat exchange assembly 1708 further comprises a third stage defined by a third heat exchanger 1720. An inlet of the third hear exchanger 1720 is in fluid communication with an outlet of the second heat exchanger. The third heat exchanger comprises a metal condensing pipe through which the exhaust fluid travels downwards. The exhaust gas dissipates heat and at least some of the exhaust gas may condense in the metal condensing pipe and fall to the base of the pipe. The metal condensing pipe comprises an outlet at its base, which comprises a condensate drainpipe 1722 to expel any condensation from the metal condensing pipe. An optional cooling fan may be provided to provide air flow over the metal condensing pipe.

The outlet of the metal condensing pipe is in fluid communication with an inlet of an extractor fan 1724 via a plastic flue pipe. Cooled exhaust gas is expelled to the external environment via an outlet of the extractor fan 1724. The smoke reduction device 1714, extractor fan 1724 and heat exchanger 1708 provided a single fluid flow path. The extractor fan may be replaced with the device illustrated in Figures 16A and 16B, for example.

Figure 17B illustrates a schematic diagram of a stove and heat exchanger arrangement that is generally similar to that of Figure 17A.

The heat exchanger in the example of Figure 17B differs from that described previously with reference to Figure 17A in that the inner pipe is closed at the inlet end, and the smoke reduction device 1714' is configured differently.

Figure 17C provides an expanded view of the smoke reduction device 1714' and a portion of the first heat exchanger 1710, 1712' of Figure 17B so that the operation of the smoke reduction device 1714' may be better understood. An exhaust fluid pipe 1724 is provided at the inlet of the heat exchanger 1710, 1712' to receive exhaust fluid from the combustion chamber and feed the exhaust fluid to the heat exchanger 1710, 1712'. Exhaust gas passes from the exhaust fluid pipe and passes along a channel defined between the inner pipe 1712' and the outer pipe 1710 of the heat exchanger. Apertures 1726 are provided in metal plate at the base of the heat exchanger and positioned laterally between the inner and outer pipes 1710, 1712'. The smoke reduction device 1714' is provided by a gas burner that has a burner rig that extends around the exterior of the exhaust fluid pipe 1724. Flames from the smoke reduction device cause hot air and flame to extend upwards into the apertures 1726 in the base of the heat exchanger. The exhaust gas is sucked over a red-hot metal plate with some small holes in it. Some air and flame is sucked through these holes, helping ignite and burn the smoke. In this way, the smoke reduction device is able to burn smoke in the exhaust fluid adjacent to the apertures 1726 while remaining outside of the exhaust flow path.

The arrangement of the smoke reduction device, or smoke burner, outside of the exhaust flow path addresses an issue that, when the flames of the smoke reduction device are within the exhaust flow path, it is difficult to increase the speed of the extractor fan 1724 without putting out the flames of the smoke reduction device. The arrangement in Figures 17B and 17C overcomes this problem by physically separating the smoke burner from the flue gas flow path from the combustion chamber.

Although Figures 17A and 17B illustrate a smoke removal device being used in conjunction with an extractor fan, experiments have shown that the smoke removal device can also be used without the extractor fan, albeit with a significant reduction in heat recovery. Nevertheless, the smoke burner's use, on its own, does make these stoves more environmentally acceptable.

Figures 17D and 17E illustrate schematic diagrams of a stove, heat exchangers without extractor fans and the smoke burner device of Figure 17C. The smoke removal device is sited at the flue outlet of the stove and generally arranged as described previously with reference to figure 1.

The hot flue gas is channelled between the inner and outer walls of a concentric flue - the inner pipe being blocked at its inlet end - forming a simple heat-exchanger. The hot gas heats up the walls, allowing a significant amount of the heat to be radiated to the room. Other heat exchangers can be used, for example the inner flue could be independently vented to the room thereby allowing airflow through the inner fluepipe, but this design is shown for simplicity. As this system relies on the "flue-effect" caused by hot air rising to suck air through the fire, care has to be taken to ensure that too much heat is not recovered by the heat exchanger, otherwise the fire will not draw.

In Figure 17E, although the exhaust path is channelled at its base to pass adjacent to the base, the heat exchanger differs from the example in Figure 17D in that there is no inner pipe. The exhaust gas may therefore use the entire volume of the heat exchanger. Smoke is sucked through it by the "flue effect" caused by hot air rising in the flue pipe.

At the base of the heat exchanger, as in the other examples, the smoke is channelled between two hot surfaces with holes in the base of the heat exchanger allowing air and flames from a clean, smokeless burner to enter. This causes the soot and particulates to burn and ignites the volatiles. This cleans and clarifies the flue gas. Although the flue pipe radiates some of the extra heat created back into the room, much of the extra heat is lost up the flue.

Figure 17F shows a photograph of a prototype retro-fit heat exchanger, in which the heat exchanger sits beside the stove. The exhaust gas passes from an outlet in the roof of the combustion chamber of the stove through a laterally disposed pipe to the top of the heat exchanger. The exhaust pass is then drawn down through the heat exchanger and passes out of a flue pipe, which may be formed of a plastics material, coupled to the bottom of the heat exchanger.

Figure 17G shows a photograph of an alternative prototype retro-fit heat exchanger, substantially similar to the prototype shown and described with reference to Figure 17F. Figure 17H illustrates a schematic diagram of a side view of a stove with a rear-mounted flue pipe with a smoke burner. The rear-mounted flue-pipe and smoke burner may be retro-fit to the stove. Smoke from a combustion chamber of the stove enters the rear mounted flue pipe via a hole sited in the back of the stove. The hole at the back of the stove and the flue pipe are in fluid communication with each other, in this example via an additional section of pipe between the hole at the back of the stove and the flue pipe. Exhaust gas containing smoke enters the flue pipe through a flue pipe inlet. The smoke is burned as it enters the flue pipe. In this example, the smoke burning is achieved using one of: a heated wire mesh or wire grid sited proximate and downstream, with reference to the exhaust gas flow, of the flue pipe inlet; or a flame provided, for example, by a Bunsen burner or similar. The burning of the smoke results in a clear and smokeless product. The heat from the stove, Bunsen burner and burnt smoke can be reclaimed by the heat exchanger further downstream, using stove arrangements as described previously with reference to the previous Figures.

Preventing smoke entering the room

There is much documentation regarding the health hazards of wood burning stoves, the most serious being the inhalation of micro-particles in the room. Particles enter the room when the stove door is opened, either to feed new material to the fire, or to poke about with it.

Conventional wood burning stoves have doors that are vertically hinged, liked domestic doors. As the door is opened, smoke is sucked from the combustion chamber into the room. This action is difficult to prevent, no matter how slowly the door is opened. Smoke can also be ejected into the room if the door is shut too quick.

According to a further aspect of the disclosure there is provided a combustion chamber with an improved door mechanism. In general terms, a solid fuel burning stove has a combustion chamber comprising an opening and a door with an open position in which at least part of the opening is unobstructed and a closed position in which the opening is sealed. In stoves of the type described with reference to figures 18A and 18B, the door is configured to be slidably moveable along a plane of the door to transition between the open and closed positions. The slidable movement may be linear or rotational, for example about a pivot that has an axis normal to the plane of the door. The slidable movement in the plane of the door means that smoke and other combustion products are not sucked out of the combustion chamber into the room when the door is transitioned from the closed position to the open position. The planer door may be flat or curved for example. In both of the examples illustrated in Figures 18A or 18B, the door is transitioned from the closed position to the open position by sliding the door upwards. However, in other examples, the door could be transitioned from the closed position to the open position by sliding the door downwards or sideways.

Figure 18A illustrates a conventional stove 1800A. The conventional stove has a pivotably mounted door that opens into the room in a conventional way, as well as a conventional locking mechanism and associated stove apparatus such as an air hole. Stove 1800B has been retrofitted with the original fixed glass panel of the outwardly opening door replaced with a slidable glass panel mounted within a pair of outer rails. Stove 1800C shows the new door formed by the slidably moveable door panel in the closed position. In this example, the new door is provided in addition to the original door of the stove. The stove 1800D illustrates the new door panel after it has been slid upwards so that the new door panel is in an open position In the open configuration, there is a substantial gap, which may have an area of greater than 50 or 100 cm², for example, allowing the fire to be stoked or loaded, and for ash to be unloaded using suitable tools like a shovel.

Figure 18B illustrates another stove with a slidably moveable door retrofitted to an existing stove. In this example, the original pivotably mounted door that opens outwardly into the room has been completely removed. Guiding rails are provided on opposing edges of the doorway to allow a door panel to be slidably mounted within the opening. The door panel is made from a toughened, heat resistant glass sheet covering most of the front of the stove. In this example, the guide rails are parallel and on the sides of the doorway. At the top and bottom of the doorway, heat sealing strips are provided to form a seal between the door panel and stove. When in the "closed" position (image on the left), with the glass slid down to the bottom stop position, very little air or smoke can get in or out of the combustion chamber, apart from through the flue. Under these circumstances, any fire in the stove will be put out.

The stove 1820B shows the door in a slightly open position to let air flow in at the base of the stove. In this slightly open position, the door panel has been slid upwards within the opposed guide rails. A thin slit opening is created, allowing air to be sucked into the combustion chamber below the fire. The height of this slit can be increased or decreased as a method of controlling the amount of air getting to the fire.

If direct physical access to the fire is required, for stoking or manipulating the fire, the glass can be slid up to a higher position (second image from the right). Stove 1820C shows an example where the door panel has been opened further to allow the fire to be stoked and air can enter the stove. Stove 1820D illustrates the stove in an open position in which the glass has been slid further upwards to allow the fire to be stoked and loaded. No negative pressure is created in the combustion chamber by doing this, unlike when opening a standard, vertically hinged stove door, where smoke would be sucked into the room. In fact, here, air flows freely into the combustion chamber, under the glass, pushing smoke back into the combustion chamber and preventing any smoke getting into the room.

If greater access to the fire is required, the glass door can be slid fully up (image on lower far right). Again, this does not create any negative pressure that would suck smoke into the room. Air is freely sucked into the combustion chamber, under the bottom edge of the glass door, preventing smoke escaping into the room.

Fully opening the door allows the fire to be built or rebuilt, or other maintenance processes to be undertaken, without smoke entering the room.

If the door is made of heat-resistant glass, any activity in the combustion chamber can be seen through the glass.

A slightly abrasive strip can be installed that cleans the glass as it is slid up and down.

The bottom edge of the glass can have a handle that protects the glass when it hits the bottom stop position.

This handle has two other functions, a) to provide something for the operator to hold onto when sliding the glass up and down and b) possibly employing a mechanism that slightly releases the glass from being clamped tightly to the stove door. This allows the glass to be slid freely up and down when squeezed, but clamps the glass hard to the door when released.

The glass door can be fit directly to the front of the stove, or it can be spaced a short distant away from the stove via a suitable air-tight spacer.

This device can be part of a new door design, or BE a retro-fit to an existing door.

A method of retro-fitting an existing stove. a) the original glass panel or whole door is removed. b) metal tracks can be fitted to the left and right sides of the opening where the glass panel or door used to be, and bolted to the outside of the door or stove. c) two heat resistant sealing strip needs to be stuck to the outside of the door, one each along the top and bottom edges where the glass panel used to be, or along the top and bottom of the stove if the whole door is to be replaced (see lower left diagram), this creates a relatively air-tight seal between the glass and the door or stove. d) a new heat-resistant glass panel, with suitable protective fixtures is slid down the tracks. A stopping device needs to be installed to stop the glass at its bottom position.

Quick fire starting method and apparatus

It is recommended to fire a wood-burning stove at nominal capacity in order to reduce smoke issues. When purchasing a stove as the primary heat source, the capacity required is almost certainly based on maximum heat requirement during the winter. If a short fire, of say 20 minutes, is required, then the stove may have to be run sub-optimally, or not at all, as it may take 20 minutes to get the fire properly started. A way of overcoming this problem is to reduce the capacity of the stove temporarily with a suitable insert - its size being based on the size of fire required.

Figures 19A and 19B illustrate a stove 1900 with an insert 1982 for reducing an effective volume for burning solid fuel 1986.

The stove 1900 has a combustion chamber 1902 having a door with a window 1984. An insert 1986 is provided within the combustion chamber 1902. The insert 1986 is formed as a round metal bowl configured to reduce an active volume of the stove for burning solid fuel. The bowl is positioned so that its opening is aligned almost vertically and also faces the window 1984 of the combustion chamber 1902. The fire is started within the reduced volume defined by the insert 1988, rather than within the larger combustion chamber 1902.

The insert 1982 may be provided with an air tube 1988 configured to engage with an air inlet 1990 of the stove 1900 and provide a passage for air to a central region at the base of the insert 1982. Rapid starting may be ensured by an optional metal tube, pointing directly toward the fire initiation point. This tube channels incoming air directly from the primary air intake to the heart of the fire. When the fire is lit (possibly with a fire lighter), it soon receives a rapid and continuous blast of air through the tube, causing it to burst into flames very quickly. The round shape of the bowl ensures that hot air is efficiently circulated to the rest of the combustible material 1986, lighting the whole fire very quickly, with minimal smoke.

The following numbered clauses are also disclosed. It will be appreciated that any of the features described with reference to the examples in the description or drawings may be provided in combination with the subject matter of these clauses. Further, it will be appreciated that the disclosed heat exchanger, stove and/or smoke removal device may be used in any combination.

Heat Exchanger

Clause 1. A heat exchange assembly for a solid fuel-burning stove, the heat exchange assembly comprising: an inlet for receiving exhaust gas from combustion within the solid fuel burning stove; one or more heat exchange elements configured to extract heat for external use from the exhaust gas and form cooled exhaust gas; an outlet for expelling the cooled exhaust gas from the heat exchange assembly; and a ventilation device coupled to the heat exchange assembly, wherein the ventilation device is configured to propel the exhaust gas towards the outlet.

2. The heat exchange assembly of any of clause 1, wherein the at least one heat exchanging elements comprise one or more flue pipes, wherein the one or more heat exchange elements are configured to extract at least 60% of the heat from the exhaust gas.

3. The heat exchange assembly of any of clause 1 or clause 2, wherein the heat exchanger and ventilation device are configured to enable the exhaust the cooled exhaust gas to have a temperature less than 60 degrees centigrade when the inlet is fed with exhaust gas at a temperature of between 250 and 600 degrees centigrade.

4. The heat exchange assembly of any preceding clause comprising a plurality of heat exchange elements placed in succession to cool the exhaust gas.

4A. The heat exchange assembly of clause 4, wherein the plurality of heat exchange elements are baffles. 4B. The heat exchange assembly of any preceding clause, wherein an ash trap is provided upstream of the plurality of heat exchange elements.

5. The heat exchange assembly of any preceding clause, wherein the ventilation device is a mechanical or electrical device.

6. The heat exchange assembly of clause 5, wherein the ventilation device comprises a fan powered by one or more of mains electricity, battery, solar cells, or wind power or by a Sterling Engine or Peltier Effect device.

7. The heat exchange assembly of any preceding clause wherein the assembly is configured to be coupled in-line between a standard solid fuel burning stove and a standard flue liner.

8. The heat exchange assembly of any preceding clause wherein the outlet is configured to be coupled to an existing chimney or a hole in the wall via a tube.

9. The heat exchange assembly of clause 8, wherein the heat exchange mechanism comprises means to circulate water to cool the exhaust gas.

10. The heat exchange assembly of clause 9, wherein the heated water is circulated through a radiator system to heat a room.

11. The heat exchange assembly of any preceding clause further comprising, at the inlet, a pre heat-exchange section comprising any one of a hot metal, ceramic, or catalysing scrim.

12. The heat exchange assembly of any preceding clause further comprising, at the outlet, a particulate filter for filtering out any remaining particles, including micro particles.

13. The heat exchange assembly of clause 12 comprising further particulate removing, gas cleaning or carbon dioxide removing means.

14. The heat exchange assembly of any preceding clause wherein the ventilation means configured to be controlled manually, by timers, by feedback mechanisms, or by mobile phone/computer, enabling the fire to be controlled and extinguished directly by the user or by remote control. 15. A stove for burning solid fuel, comprising: a combustion chamber; and the heat exchange assembly of any preceding clause; wherein the flue inlet is in fluid communication with the combustion chamber to receive the exhaust gas from the combustion chamber.

16. The stove of clause 15, wherein the combustion chamber comprises an air inlet.

17. The stove of clause 15 or clause 16, further comprising an air inlet pipe section coupled to the solid fuel burning stove.

18. The stove of clause 17, wherein the outlet comprises a flue outlet pipe section, and wherein the air inlet pipe section and flue outlet pipe section are concentric, thus forming a coaxial pipe so as to form a "balanced" flue system.

19. The stove of any of clauses 15-18, wherein the stove has the visual, functional and psychological advantages of a standard domestic solid fuel burning stove.

20. The stove of any of clauses 15-19, wherein the stove further comprises a blind chimney section coupled to the combustion chamber.

21. The stove of clause 20, wherein the blind chimney is detachably coupled to the combustion chamber.

Clause 22. A method of retrofitting a heat exchanger of any preceding clause to a stove installation, comprising: removing a section of flue pipe from a stove installation; and coupling the inlet and outlet of the heat exchange assembly to respective openings in the stove installation created by the removal of the section of the flue pipe.

Heat exchanger / Stove comprising a heat exchanger

Clause 1. A domestic wood burning or solid fuel burning stove, where a heat exchanger, (or sequence of heat exchangers) is used to cool the flue gas to room temperature (+/- 60 degrees Celsius), while maintaining the relaxing appearance and ambiance of a normally aspirated wood-burning stove, at the same time preventing heat being wasted and recovering this heat for useful purposes - the process being facilitated by the normal flow of rising hot flue gas being replaced by means of a suction device sited after the heat exchanger(s).

2. The domestic wood burning or solid fuel burning stove of clause 1, where the suction device is an electric fan.

3. As clause 1, where the suction device is mechanical.

4. As clause 1, where the smoke and volatile gases leaving the combustion chamber are burnt to remove smoke, soot, carbon monoxide and other volatile gasses, before entering the heat exchanger(s), resulting in the flue gas being smoke-free, and at the same time producing more energy from the fire, which is captured by the heat exchanger, thereby resulting in the stove being more than 100% efficient, and preventing any buildup of creosote or soot in the flue pipe or heat exchanger.

5. As clause 4, where the flue pipe passes through or extremely close to the main fire, enabling the flue gas inside to be heated, ignited and burnt by the main fire.

6. As clause 4, where the flue gas passes through, or extremely close to a second independent smokeless fire or electric device, where the flue gas is ignited and burnt.

7. As any of the clauses above, where the flue pipe, after the (last) heat exchanger, is plastic.

8. As any of the clauses above, where the cooled, flue gas is expelled through an existing chimney, a hole in the wall or directly to the atmosphere.

9. As clause 1, where the device is a retro-fit, fitted to an already established, or new solid fuel or wood-burning stove.

10. As clause 1, where the door slides up and down, reducing the amount of smoke entering the room when the door is opened or closed.

11. As clause 1, where the stove is a custom design, incorporating an internal flue that guides smoke, rising from the fire, downward and out the lower part of the stove. 12. As clause 1, where the power of the suction device is controllable, enabling various functions during different phases of the fire, under the direct, or remote control of the operator or an electronic device.

13. As clause 12, where the suction device can temporarily become a blowing device if required.

14. As any of the previous clauses, where the stove can be fitted anywhere in a property, without the need for a chimney or flue liners.

15. As clause 14, where the stove can be mobile, being movable from room to room or into the garden occasionally.

16. As clause 1, where the parts outside the combustion chamber are easily accessible, low-cost, simple to maintain and readily replaceable.

17. As clause 1, where part of the heat exchanger consists of two concentric pipes, hot flue gas passing between the inner pipe and the outer pipe, creating a very hot outer pipe that readily radiates and convects heat.

18. As clause 1, where the suction device is sited after the heat exchanger, ensuring the whole system before that is running at negative pressure, enabling the system to be slightly leaky without compromising safety.

Heat exchanger / Stove comprising a heat exchanger - further alternative (1)

A domestic wood burning or solid fuel burning stove, where the role of the flue is replaced by a device that emulates the "chimney effect", thereby eliminating the need for a chimney and any constraints associated with the "chimney effect"; one advantage being to enable hot gas, emanating from the fire, to be cooled to room temperature, or even below room temperature, with all the heat being recovered and put to useful purpose, the process having no effect on the functionality or visual appearance of the fire.

Heat exchanger / Stove comprising a heat exchanger - further alternative (2)

A domestic wood burning or solid fuel burning stove, where all or part of the flue is replaced by a means that emulates the "chimney effect", thereby eliminating the need for a chimney and many of the factors associated with the "chimney effect", such as pipe size, length, orientation, siting, complete air-tightness and most notably, allowing the hot gas, emanating from the fire, to be captured and cooled to near, or even below, room temperature; the cooled gas being released to the atmosphere through an unrestrained choice of plastic, metal, or ceramic pipes, and the heat recovered being put to useful purpose, effectively making the rated stove efficiency almost 100% - yet still retaining the functionality, visual appearance or psychological ambience of a normal wood-burning gas stove.

Heat exchanger / Stove comprising a heat exchanger - further alternative (3)

A domestic or commercial Wood-burning or solid fuel burning stove, where all or part of the flue is replaced by means that eliminates the need for the "chimney effect", and even the chimney itself, by using a very efficient heat exchanger, followed by a gas extractor device, and at the same time eliminating the need for many of the factors associated with the "chimney effect", such as the necessity for complete air-tightness, restrictions on pipe diameter, length, orientation, and siting of the stove, and the percentage of heat that is allowed to be recovered before the "chimney effect" is destroyed, whereas by contrast, this new means allows the hot gas, emanating from the fire, to be captured and, by use of the heat exchanger, or sequence of heat exchangers, cooled to near, or even below room temperature; the cooled gas being released to the atmosphere through a choice of plastic, metal, ceramic or other type of pipe, and the heat recovered being put to useful purpose, thereby making the rated stove efficiency near 100% while retaining much of the functionality, visual appearance and ambience of a normal wood-burning stove.

Heat exchanger / Stove comprising a heat exchanger - further alternative (4)

A domestic wood-burning or solid fuel burning stove, where a negative pressure inducing device (NPID) is used to capture hot flames, gas and smoke emanating from the top of the fire and sucks them through a heat exchanger or sequence of heat exchangers, cooling them to near or below room temperature before they reach the NPID; the negative pressure eliminating the absolute necessity for a completely air-tight gas train in the heat exchanger(s) and any pipework before the NPID, and allowing any structures after the heat exchanger(s) to be made of low melting-point plastic, if required.

Heat exchanger / Stove comprising a heat exchanger - further alternative (5)

A domestic wood-burning or solid fuel burning stove, where a negative pressure inducing device (NPID), sited at, or just before the final exhaust outlet, is used to create negative pressure in the heat train, from the air input of the combustion chamber up to the NPID; this negative pressure being used to suck air through the fire, then through a heat exchanger or sequence of heat exchangers, and any flue gas cleaning devices; the heat exchangers being designed to cool the hot gas to near or below room temperature, thereby recovering nearly all the heat for useful purposes and allowing subsequent devices, such as pipework, the NPID, and final exhaust pipe to be made of heat-sensitive material, such as plastic, if desired; the negative pressure eliminating the necessity for completely air-tight joints in the heat train, enabling easy installation, maintenance and replacement of parts.

Heat exchanger / Stove comprising a heat exchanger - further alternative (6)

A domestic wood-burning or solid fuel burning stove, where a negative pressure inducing device (NPID), sited at, or just before the exhaust outlet, is used to create negative pressure in the heat train, from the air input of the combustion chamber through to the NPID; the negative pressure being used to suck air through the fire, through any flue gas cleaning device(s) then through a heat exchanger or sequence of heat exchangers; the heat exchangers being designed to cool the hot gas to near or below room temperature, thereby enabling recovery of nearly all the heat for useful purposes and allowing any subsequent devices, such as pipework, the NPID, and final exhaust pipe to be made of heat-sensitive material, such as plastic; the negative pressure eliminating the necessity for completely air-tight joints or parts in the heat train, thereby reducing design constraints, and enabling the use of low- cost modular components that are easily installed, maintained and replaced.

Heat exchanger / Stove comprising a heat exchanger - further alternative language (7)

A domestic wood-burning or solid fuel burning stove, cooker or open fire-place together with it's associated flue system, where an electrical or mechanical suction device, sited at, or just before the outlet of the flue, is used to suck flue gas through the heat train, which includes a very efficient heat exchanger, or sequence of heat exchangers; the heat exchanger(s) being designed to cool the hot gas, generated in a combustion chamber or open fire-place, to near to, or below room temperature, thereby recovering nearly all the heat from the flue gas, together with the latent heat of any condensing water vapour, and allowing any subsequent devices, including pipework, the suction device, and final exhaust pipe to be made of heat-sensitive material, such as plastic; the reduced pressure in the heat train eliminating the need for completely air-tight components or joints, small inward air-leaks being tolerated, and allowing the use of lower specification components that are simple to install and are easily maintained, replaced or dismantled.

Smoke Reduction

Clause 1. A smoke reduction device for removing smoke produced by a solid fuelburning fire of a solid fuel-burning stove, comprising: a device inlet configured to receive exhaust fluid containing smoke from the stove; a device outlet for expelling exhaust fluid from the device; and an ignition arrangement between the device inlet and device outlet and arranged to burn at least some smoke from the stove so that the smoke content of the exhaust fluid expelled from the burner outlet is reduced.

2. The smoke reduction device of clause 1, wherein the ignition arrangement is a heat source.

3. The smoke reduction device of clause 2, wherein the heat source is arranged such that the carbon monoxide or solid particulate content of the exhaust fluid expelled from the burner outlet is reduced.

4. The smoke reduction device of any of clauses 2-3, wherein the heat source is one of: a burner, a smokeless solid fuel burner, a gas burner, a liquid fuel burner, and an electrical heating element.

5. The smoke reduction device of any of clauses 2-4, wherein the heat source is configured to generate a negative pressure thereby drawing the exhaust gas though the burner inlet.

6. The smoke reduction device of clause 1, wherein the device comprises a conduit between the device inlet and device outlet and the ignition arrangement is at least an intermediate section of the conduit that is proximate the solid fuel-burning fire when the stove is in use to facilitate ignition of at least some smoke in the conduit so that the smoke content of the exhaust fluid expelled from the assembly outlet is reduced. 7. The device of clause 6, wherein the intermediate section of the conduit comprises one or more ignition features to facilitate ignition of at least some smoke in the conduit so that the smoke content of the exhaust fluid expelled from the assembly outlet is reduced.

8. The device of clause 7, wherein the one or more ignition features are one or more openings in the conduit.

9. The device of clause 8, wherein the one or more openings are configured to allow flames and/or hot ash to move into the conduit.

10. The device of clause 9, wherein the conduit further comprises a filter configured to trap ash, the filter being positioned between the one or more openings and the assembly outlet.

11. The device of clause 7, wherein the one or more ignition features are one or more baffles arranged within the conduit and configured to transfer at least some of the heat from the solid-fuel burning fire to at least some of the smoke in the conduit to facilitate ignition of the at least some of the smoke in the conduit.

12. The device of any of clauses 6-11, wherein the intermediate section of the conduit that is proximate the solid fuel-burning fire when the stove is in use is arranged at any one of: above the fire, below the fire, and adjacent the fire.

13. The device of any of clauses 6-12, wherein the smoke reduction assembly further comprises a secondary air inlet between the assembly inlet and the assembly outlet, wherein the secondary air inlet comprises an adjustment mechanism configured to vary the amount of air introduced into the conduit through the inlet.

14. The device of clause 13, wherein the secondary air inlet is between the assembly inlet and the one or more ignition features.

15. A stove for burning solid fuel comprising: a combustion chamber for containing the solid fuel-burning fire; and the smoke reduction device of any preceding clause; wherein the inlet of the smoke reduction device is in fluid communication with the combustion chamber to receive the exhaust gas from the combustion chamber.

16. A heat exchange assembly comprising: an heat exchange inlet for receiving exhaust fluid from combustion within the solid fuel burning stove; one or more heat exchange elements configured to extract heat for external use from the exhaust gas and form cooled exhaust fluid; a heat exchange outlet for expelling the cooled exhaust fluid from the heat exchange assembly; a ventilation device configured to propel the exhaust fluid towards the heat exchange outlet; and the smoke reduction device of any preceding clause.

17. The heat exchange assembly of clause 16, wherein the heat exchange assembly inlet and the device inlet are in fluid communication with the combustion chamber to receive the exhaust fluid from the combustion chamber.

18. The heat exchange assembly of clause 16 or clause 17, wherein the ventilation device is arranged to receive exhaust fluid that has passed through the smoke reduction device.

18A. The heat exchange assembly of clause 16 or clause 17, wherein the ventilation device is arranged to receive exhaust fluid that has not passed through the smoke reduction device.

19. The heat exchange assembly of any of clauses 18 to 18, wherein the ventilation device is arranged to receive cooled exhaust fluid that has passed through the heat exchange assembly.

20. The heat exchange assembly of any of clauses 16 to 19, wherein the heat exchange assembly is arranged to receive exhaust fluid that has passed through the smoke reduction device.

21. The heat exchange assembly of any of clauses 16 to 20, wherein the smoke reduction device, ventilation device and heat exchanger are provided along a single fluid flow path.

22. The heat exchange assembly pf any of clauses 16 to 20, wherein the ventilation device and heat exchanger are provided along a single fluid flow path and the smoke reduction device is provided outside of the single fluid flow path. 23. The heat exchange assembly of clause 22, wherein the heat exchanger has a base portion comprising apertures, and wherein the smoke reduction device is configured to heat the base portion.

24. The heat exchange assembly of clause 23, wherein the base portion comprises apertures.

25. A method of reducing smoke expelled from a stove, comprising: activating the heat source of the smoke reduction device of clause 2; and subsequently, igniting a stove fire in a combustion chamber of the solid fuel burning stove.

26. The method of clause 22, further comprising: deactivating the heat source of the smoke reduction device in response to any of: the stove fire temperature exceeding a temperature threshold; the time since igniting the stove fire has exceeded a time threshold; and a visual indication that the smoke produced by the stove fire has reduced.

Smoke Reduction Device

Clause 1. A smoke reduction device for removing smoke produced by a stove, comprising: a device inlet configured to receive exhaust fluid containing smoke from the stove; a device outlet for expelling exhaust fluid from the device; and a heat source or heat-transmission structure between the device inlet and device outlet and arranged to burn at least some smoke from the stove so that the smoke content of the exhaust fluid expelled from the burner outlet is reduced.

2. The smoke reduction device of clause 1, wherein the heat source is arranged such that the carbon monoxide or solid particulate content of the exhaust fluid expelled from the burner outlet is reduced.

3. The smoke reduction device of clause 1, wherein the heat source is one of: a burner, a smokeless solid fuel burner, a gas burner, a liquid fuel burner, and an electrical heating element. 4. The smoke reduction device of clause 1, wherein the heat source is configured to generate a negative pressure thereby drawing the exhaust gas though the burner inlet.

4A. The smoke reduction device of any preceding clause further comprising a housing having the inlet and the outlet, wherein the heat source is provided within the housing.

Clause 5. A stove for burning solid fuel comprising: a combustion chamber; and the smoke reduction device of any preceding clause; wherein the burner inlet of the smoke reduction device is in fluid communication with the combustion chamber to receive the exhaust gas from the combustion chamber.

6. The stove of clause 5, further comprising a heat exchange assembly comprising: an heat exchange inlet for receiving exhaust fluid from combustion within the solid fuel burning stove; one or more heat exchange elements configured to extract heat for external use from the exhaust gas and form cooled exhaust fluid; a heat exchange outlet for expelling the cooled exhaust fluid from the heat exchange assembly; and a ventilation device coupled to the heat exchange assembly, wherein the ventilation device is configured to propel the exhaust fluid towards the heat exchange outlet.

7. The stove of clause 6, wherein the heat exchange assembly inlet and the device inlet are in fluid communication with the combustion chamber to receive the exhaust fluid from the combustion chamber.

8. The stove of clause 6 or clause 7, wherein the ventilation device is arranged to receive exhaust fluid that has passed through the smoke reduction device.

9. The stove of any of clauses 6 to 8, wherein the ventilation device is arranged to receive cooled exhaust fluid that has passed through the heat exchange assembly.

10. The stove of any of clauses 6 to 9, wherein the heat exchange assembly is arranged to receive exhaust fluid that has passed through the smoke reduction device. 11. The stove of any of clauses 6 to 10, wherein the smoke reduction device, ventilation device and heat exchanger are provided along a single fluid flow path.

12. The stove of any of clauses 6 to 11, further comprising a controller configured to control operation of the smoke reduction device in accordance with a smoke level.

Method of removing smoke

Clause 13. A method of reducing smoke expelled from a stove, comprising: activating the heat source of the smoke reduction device of claim 1; and subsequently, igniting a stove fire in a combustion chamber of the solid fuel burning stove.

14. The method of clause 13, further comprising: deactivating the heat source of the smoke reduction device in response to any of: the stove fire temperature exceeding a temperature threshold; the time since igniting the stove fire has exceeded a time threshold; and a visual indication that the smoke produced by the stove fire has reduced.

15. The method of clause 13 or 14, further comprising: adding fuel underneath the stove fire such that the fuel is not in direct contact with the fire; and after a period of time, moving the fuel into direct contact with the fire.

16. The method of any one of clauses 13 to 15, further comprising: activating the ventilation device of the heat exchange assembly.

Solid fuel burning stove comprising a smoke reduction assembly

Clause 1. A stove for burning solid fuel comprising: a combustion chamber for containing a solid fuel-burning fire; and a smoke reduction assembly comprising: an assembly inlet configured to receive exhaust fluid containing smoke from the stove; an assembly outlet for expelling exhaust fluid from the assembly; and a conduit between the assembly inlet and assembly outlet, wherein at least an intermediate section of the conduit is proximate the solid fuelburning fire when the stove is in use to facilitate ignition of at least some smoke in the conduit so that the smoke content of the exhaust fluid expelled from the assembly outlet is reduced.

2. The stove of clause 1, wherein the intermediate section of the conduit comprises one or more ignition features to facilitate ignition of at least some smoke in the conduit so that the smoke content of the exhaust fluid expelled from the assembly outlet is reduced.

3. The stove of clause 2, wherein the one or more ignition features are one or more openings in the conduit.

4. The stove of any of clauses 2-3, wherein the one or more openings are configured to allow flames and/or hot ash to move into the conduit.

5. The stove of clause 4, wherein the conduit further comprises a filter configured to trap ash, the filter being positioned between the one or more openings and the assembly outlet.

6. The stove of clause 2, wherein the one or more ignition features are one or more baffles arranged within the conduit and configured to transfer at least some of the heat from the solid-fuel burning fire to at least some of the smoke in the conduit to facilitate ignition of the at least some of the smoke in the conduit.

7. The stove of any preceding clause, wherein the intermediate section of the conduit that is proximate the solid fuel-burning fire when the stove is in use is arranged at any one of: above the fire, below the fire, and adjacent the fire.

8. The stove of any preceding clause, wherein the smoke reduction assembly further comprises a secondary air inlet between the assembly inlet and the assembly outlet, wherein the secondary air inlet comprises an adjustment mechanism configured to vary the amount of air introduced into the conduit through the inlet.

9. The stove of clause 8, wherein the secondary air inlet is between the assembly inlet and the one or more ignition features. 10. The stove of any preceding clause, further comprising a heat exchange assembly comprising: a heat exchange inlet for receiving exhaust fluid from combustion within the solid fuel burning stove; one or more heat exchange elements configured to extract heat for external use from the exhaust gas and form cooled exhaust fluid; a heat exchange outlet for expelling the cooled exhaust fluid from the heat exchange assembly; and a ventilation device coupled to the heat exchange assembly, wherein the ventilation device is configured to propel the exhaust fluid towards the heat exchange outlet.

11. The stove of clause 10, wherein the heat exchange assembly inlet and the smoke reduction assembly inlet are in fluid communication with the combustion chamber to receive the exhaust fluid from the combustion chamber.

12. The stove of clause 10 or clause 11, wherein the ventilation device is arranged to receive exhaust fluid that has passed through the smoke reduction assembly.

13. The stove of any of clauses 10 to 12, wherein the ventilation device is arranged to receive cooled exhaust fluid that has passed through the heat exchange assembly.

14. The stove of any of clauses 10 to 13, wherein the heat exchange assembly is arranged to receive exhaust fluid that has passed through the smoke reduction assembly.

15. The stove of any of clauses 10 to 14, wherein the smoke reduction assembly, ventilation device and heat exchanger are provided along a single fluid flow path.

16. The stove of any of clauses 10 to 15, further comprising an insulating cover arranged concentrically on the outer surface of the conduit configured to slide over at least a portion of the ignition features to control the extent of ignition of the smoke in the conduit.

Method of reducing smoke using a solid fuel burning stove comprising a smoke reduction assembly

Clause 17. A method of reducing smoke expelled from a stove, comprising: positioning solid fuel within the combustion chamber of the stove of clause

1; and igniting the solid fuel.

Fluid flow reversal mechanism

Clause 1. A fluid flow reversal mechanism for reversing the flow of fluid provided by a motorised fan, the fluid flow reversal mechanism comprising: a first fluid port, a second fluid port, and a motorised fan therebetween, the motorised fan comprising a fan inlet and a fan outlet; wherein, in a first configuration, the first fluid port is in fluid communication with the fan inlet and the second fluid port is in fluid communication with the fan outlet such that fluid flows from the first fluid port to the second fluid port; wherein, in a second configuration, the second fluid port is in fluid communication with the fan inlet and the first fluid port is in fluid communication with the fan outlet such that fluid flows from the second fluid port to the first fluid port.

2. The gas flow reversal mechanism of clause 1, further comprising: a fan conduit; a first auxiliary conduit; and a second auxiliary conduit; wherein the fan conduit, the first auxiliary conduit and the second auxiliary conduit branch from a first node and terminate at a second node; wherein the first fluid port is coupled to the fan conduit, the first auxiliary conduit and the second auxiliary conduit via the first node and the second fluid port is coupled to the fan conduit, the first auxiliary conduit and the second auxiliary conduit via the second node; wherein the motorised fan is disposed in line with the fan conduit between the first node and the second node; wherein a first valve is disposed at the first node and a second valve is disposed at the second node, wherein the first and second valves are operable together in one of a first valve configuration and second valve configuration; wherein, in the first valve configuration: the first valve allows fluid communication between the first fluid port and the fan conduit and the first valve blocks fluid communication between the first auxiliary conduit and the fan inlet, and the second valve allows fluid communication between the second fluid port and the fan conduit and blocks fluid communication between the second auxiliary conduit and the fan outlet; and wherein, in the second valve configuration: the first valve blocks fluid communication between the first fluid port and both of the fan conduit and the first auxiliary conduit and allows fluid communication between the first auxiliary conduit and the fan inlet via the fan conduit; and the second valve blocks fluid communication between the second fluid port and both of the fan conduit and the second auxiliary conduit and allows fluid communication between the second auxiliary conduit and the fan outlet via the fan conduit; wherein, in the first configuration, the valves are in the first valve configuration such that the fan draws fluid to the fan inlet from the first fluid port via the fan conduit and the fan forces fluid from the fan outlet to the second fluid port via the fan conduit; wherein, in the second configuration, the valves are in the second valve configuration such that the motorised fan draws fluid from the second fluid port to the fan inlet via the first auxiliary conduit and forces fluid from the fan outlet to the first fluid port via the second auxiliary conduit.

2A. The gas flow reversal mechanism of clause 1, further comprising: a fan conduit comprising a first end coupled to the first fluid port and a second end coupled to the second fluid port, wherein the motorised fan is disposed between the first end of the fan conduit and the second end of the fan conduit; a first auxiliary conduit comprising a first end coupled to the first end of the fan conduit via a first valve and a second end coupled to the second end of the fan conduit; a second auxiliary conduit comprising a first end coupled to the first end of the fan conduit and a second end coupled to the second end of the fan conduit via a second valve; wherein, in the first configuration, the first valve and the second valve are closed such that the first fluid port is in fluid communication with the fan inlet and the second fluid port is in fluid communication with the fan outlet such that fluid flows from the first fluid port to the second fluid port, and, in the second configuration: the first valve is open such that the first fluid port is in fluid communication with the fan outlet via the second auxiliary conduit and first fluid port is blocked from being in fluid communication with the fan conduit such that the first fluid port is not in fluid communication with the fan inlet; and the second valve is open such that the second fluid port is in fluid communication with the fan inlet via the first auxiliary conduit and the second fluid port is blocked from being in fluid communication with the fan conduit such that the second fluid port is not in fluid communication with the fan outlet.

3. The gas flow reversal mechanism of clause 1 or clause 2, wherein: the first valve is hinged at a point where the first fluid port couples to the first auxiliary conduit such that, in the first valve configuration, the first valve is in a first position that blocks the opening of the first auxiliary conduit at the first node and, in the second valve configuration, the first valve is rotates about the hinge into a second position in which the first auxiliary conduit is in fluid communication with the fan inlet via the fan conduit and the first fluid port is in fluid communication with the second auxiliary conduit; and the second valve is hinged at a point where the second fluid port couples to the second auxiliary conduit such that, in the first valve configuration, the second valve is in a first position that blocks an opening of the second auxiliary conduit at the second node and, in the second valve configuration, the second valve rotates about the hinge to a second position in which the second auxiliary conduit is in fluid communication with the fan outlet via the fan conduit and the second fluid port is in fluid communication with the first auxiliary conduit.

Sliding door

Clause 1. A solid fuel burning stove comprising: a combustion chamber having an opening for loading and unloading the combustion chamber with solid fuel; and a door for the opening that is slidably moveable between an open position and a closed position.

2. The stove of clause 1, wherein the door is arranged to slidably move in a linear direction along a vertical axis.

3. The stove of clause 1 or clause 2, wherein the door may be slid upwards when in use to move from the closed position to the open position.

4. The stove of any preceding clause, wherein the door is arranged to slidably move along a plane of the door. 5. The stove of any preceding clause wherein the door comprises a door panel and a pair of tracks or guides provided in parallel, wherein the door panel is configured to slide along, and between, the pair of tracks or guides.

6. The stove of any preceding clause wherein the tracks are configured to receive a opposed pair of parallel edges of the door.

7. The stove of any preceding clause wherein the door is rectangular and the opening is rectangular.

8. The stove of clause 4, wherein the door is pivotably coupled to slidably move along the plane of the door.

9. The stove of any preceding clause, wherein the door is arranged such that, when the door is moved into the open position, air is sucked into the combustion chamber.

10. The stove of any preceding clause, wherein the opening has an area greater than 100 cm² when in the open position.

11. The stove of any preceding clause, comprising one or more sealing elements adjacent the opening and configured to engage with the door to form a seal.

12. The stove of clause 11, wherein the door is slidably moveable relative to the sealing elements.

13. The stove of any preceding clause, wherein in the closed position, the door is sealed to prevent air from entering the stove such that fire cannot be sustained in the stove.

14. The stove of any preceding clause, wherein the door comprises a handle along any of: a bottom edge or a top edge.

15. The stove of any preceding clause, wherein a sealing element is disposed at each of a top edge and a bottom edge of the opening such that, in the closed position, the top and bottom seals are engaged with the door, and in the one or more open positions the top seal maintains engagement with the door as the door is moved along the vertical axis.

Stove Insert 1. A method for temporarily reducing a capacity of a combustion chamber of a domestic solid fuel burning stove by inserting a metal bowl within the combustion chamber and orientating the metal bowl in a near vertical position facing the stove door.

2. A stove comprising: a combustion chamber having a door; a removable bowl within the combustion chamber, wherein the bowl is orientated to face the door.

The bowl may be a round bowl.

3. An insert for a chamber of a domestic solid fuel burning stove, the insert comprising a metal bowl configured to reduce an active volume of the stove for burning wood.

4. The insert of clause 4 comprising an air tube configured to engage with an air inlet of the stove and provide a passage for air to a central region at the base of the insert.

Claims

1. A heat exchange assembly for a domestic stove, the heat exchange assembly comprising: an inlet for receiving exhaust gas from combustion within the solid fuel burning stove; one or more heat exchange elements configured to extract heat for external use from the exhaust gas and form cooled exhaust gas; an outlet for expelling the cooled exhaust gas from the heat exchange assembly; and a ventilation device configured to propel the exhaust gas towards the outlet, wherein the ventilation device is provided downstream, with reference to exhaust gas flow, from the one or more heat exchange elements, wherein the heat exchange assembly and ventilation device are configured to enable the cooled exhaust gas to have a temperature less than 60 degrees centigrade when the inlet is fed with exhaust gas at a temperature of between 250 and 600 degrees centigrade.

2. The heat exchange assembly of claim 1, wherein the heat exchange assembly and ventilation device are configured to cool the flue gas such that water vapour in the exhaust gases condenses and releases latent heat.

3. The heat exchange assembly of claim 1, wherein the heat exchange assembly and ventilation device are configured to enable the exhaust the cooled exhaust gas to have a temperature less than room temperature.

4. The heat exchange assembly of any preceding claim, wherein the ventilation device is a mechanical or electrical device.

5. The heat exchange assembly of any preceding claim, wherein the ventilation device is formed of plastic material and comprises one of a fan, bellows, or venturi effect device.

6. The stove of any preceding claim, wherein at least a section of flue pipe, and any other devices, coupled to the outlet of the heat exchange assembly comprise plastics material.

7. The heat exchange assembly of claim 1, wherein the at least one heat exchanging elements comprise one or more flue pipes, wherein the one or more heat exchange elements are configured to extract at least 60% of the heat from the exhaust gas.

8. The heat exchange assembly of any preceding claim comprising a plurality of heat exchange elements placed in succession to cool the exhaust gas.

9. The heat exchange assembly of any preceding claim wherein the heat exchange assembly outlet is configured to be coupled to an existing chimney or a hole in the wall via a tube.

10. The heat exchange assembly of claim 8, wherein the heat exchange mechanism uses water to cool the exhaust gas.

11. The heat exchange assembly of any preceding claim, wherein part of the heat exchange assembly forms a radiator system to heat a room.

12. The heat exchange assembly of any preceding claim further comprising a smoke reduction device for removing smoke produced by a solid fuel-burning fire of the stove, comprising: a device inlet configured to receive exhaust gas containing smoke from the stove; a device outlet for expelling exhaust gas from the device; and an ignition arrangement between the device inlet and device outlet and arranged to burn at least some smoke from the stove so that the smoke content of the exhaust gas expelled from the burner outlet is reduced.

13. The heat exchange assembly of claim 12, wherein the ignition arrangement comprises a heat source.

14. The heat exchange assembly of claim 12 or claim 13, wherein the heat source is arranged such that the carbon monoxide or solid particulate content of the exhaust fluid expelled from the burner outlet is reduced.

15. The heat exchange assembly of any of claims 12 to 14, wherein the heat source is one of: a burner, a smokeless solid fuel burner, a gas burner, a liquid fuel burner, and an electrical heating element.

16. The heat exchange assembly of claim 15, wherein the ignition arrangement comprises conduit between the device inlet and device outlet, wherein at least an intermediate section of the conduit is proximate the solid fuel-burning fire when the stove is in use to facilitate ignition of at least some smoke in the conduit so that the smoke content of the exhaust fluid expelled from the assembly outlet is reduced.

17. The heat exchange assembly of any preceding claim, wherein the combustion chamber has an opening for loading and unloading the combustion chamber with solid fuel; and a door for the opening that is slidably moveable between an open position and a closed position.

18. The heat exchange assembly of claim 17, wherein the door is arranged to slidably move in a linear direction along a vertical axis.

19. The stove of any preceding claim further comprising, at the inlet, a pre heatexchange section comprising any one of a hot metal, ceramic, or catalysing scrim.

20. The heat exchange assembly of any preceding claim further comprising, at the outlet, a particulate filter for filtering out any remaining particles, including micro particles.

21. The heat exchange assembly of any preceding claim comprising further particulate removing, gas cleaning or carbon dioxide removing means.

22. The heat exchange assembly of any preceding claim wherein the ventilation means is configured to be controlled by timers, by feedback mechanisms, or by mobile phone/computer, enabling the fire to be controlled and extinguished directly by the user or by remote control.

23. The heat exchange assembly of any preceding claim, comprising two concentric pipes configured to guide exhaust gas to pass between the inner pipe and the outer pipe.

24. A domestic stove, comprising: a combustion chamber; and the heat exchange assembly of any preceding claim; wherein the inlet of the heat exchanger is in fluid communication with the combustion chamber to receive the exhaust gas from the combustion chamber.

25. The domestic stove of claim 24, wherein the stove is for burning solid fuel.

26. The domestic stove of claim 24 or 25, wherein the stove is a wood-burning stove.

27. The domestic stove of any of claims 24 to 26, wherein the domestic stove is configured to provide a power output of up to 20 kW when burning the solid fuel.

28. The domestic stove of any of claims 24 to 26, wherein the domestic stove is configured to provide a power output of up to 5 kW when burning the solid fuel.

29. The heat exchange assembly of any of claims 24 to 28, wherein the ventilation device is configured to generate a negative pressure in the combustion chamber and heat exchange assembly.

30. The heat exchange assembly of claim 29, wherein the negative pressure generated by the ventilation device prevents leakage from the combustion chamber into the environment, eliminating the need for completely air-tight components or joints, small inward air-leaks being tolerated, and allowing the use of lower specification components that are simple to install and are easily maintained, replaced or dismantled.

31. The domestic stove of any of preceding claim wherein the stove comprises a flue pipe and the heat exchange assembly is provided between the inlet and outlet of a flue pipe.

32. The domestic stove of any preceding claim, wherein at least a section of the flue pipe coupled to the outlet of the heat exchanger comprises plastics material.

33. The domestic stove of any preceding claim further comprising a standard flue liner or flue pipe and wherein the heat exchange assembly is configured to be retro-fit in-line between the stove and the standard flue liner or flue pipe.

34. The domestic stove of any of claims 24 to 33, wherein the inlet of the heat exchanger is coupled to the top of the combustion chamber.

35. The domestic stove of claim 34, wherein the inlet of the heat exchanger is directly coupled to the top of the combustion chamber.

36. The domestic stove of any of claims 24 to 35, wherein the combustion chamber comprises an air inlet, wherein the stove has a gas flow path that passes upwards through the stove from the air inlet, through and out of the top of the combustion chamber.

37. The domestic stove of any of claims 24 to 36, wherein the combustion chamber has a window for viewing the fire within the combustion chamber.

38. The domestic stove of claim 37, wherein the stove has the visual, functional and psychological advantages of a standard domestic solid fuel burning stove.

39. The domestic stove of any of claims 24 to 38, further comprising an air inlet pipe section coupled to the solid fuel burning stove, wherein the outlet comprises a flue outlet pipe section, and wherein the air inlet pipe section and flue outlet pipe section are concentric, thus forming a coaxial pipe so as to form a "balanced" flue system.

40. The domestic stove of any of claims 24-39, wherein the stove further comprises a blind chimney section coupled to the combustion chamber.

41. The domestic stove of claim 40, wherein the blind chimney is detachably coupled to the combustion chamber.

42. A method of retrofitting a heat exchanger of any of claims 1 to 26 to a domestic stove installation, comprising: removing a section of flue pipe from a stove installation; and coupling the inlet and outlet of the heat exchange assembly to respective openings in the stove installation created by the removal of the section of the flue pipe.

43. An insert for a chamber of a domestic solid fuel burning stove, the insert comprising a metal bowl configured to reduce an active volume of the stove for burning wood.

44. The insert of claim 43 comprising an air tube configured to engage with an air inlet of the stove and provide a passage for air to a central region at the base of the insert.