IE51450B1 - Solid fuel stove - Google Patents

Abstract

A solid fuel stove adapted for use as a continuous combustion or heating stove, comprises a combustion chamber (11), a front charging opening to the combustion chamber, an ashbox (12) located below the combustion chamber, a grate (13) arranged in a lower region of the combustion chamber, an inlet arranged to supply combustion air to the combustion chamber through the grate, an upper outlet (19) for exhaust gases arranged in an upper region of the combustion chamber, the upper outlet (19) being closable, and an additional, lower outlet (31) for exhaust gases arranged in a side wall of the combustion chamber in a region of the combustion chamber located directly above the grate.

Description

This invention relates to a solid fuel stove comprising a housing, a combustion chamber arranged in the housing, a charging opening to the combustion chamber, an ashbox below the combustion chamber, a grate arranged in a lower region of the combustion chamber, an inlet arranged to supply combustion air to the combustion chamber through the grate, an oven compartment arranged in the housing adjacent to the combustion chamber, a hot plate, and exhaust gas ducting communicable with the combustion chamber and arranged so as to be able to convey exhaust gases from the combustion chamber so as to heat the oven compartment and/or the hot plate.

In a solid fuel stove for heating food the hotplate is heated from below by the hot waste combustion gases and gives off its heat to a food container on the hot-plate. When the hot-plate is to be brought to a high temperature for a limited time (cooking time), any solid fuel can be used, from wood and peat, through brown coal to pit coal and coke. If the stove is also to heat the room in which it is installed, and continually, not only at cooking times, then this is a continuous combustion stove. The essential difference in structure of a continuous combustion stove from a stove used only for cooking consists in that the firebrick-coated combustion chamber is designed as a charging hopper and in that special waste gas ducts are provided which guarantee good radiation of heat into the room in which it is installed. Continuous combustion stoves are usually provided with a height-adjustable grate, whereby purely for cooking purposes, - 2 51450 the grate is brought into its highest position, nearest the hot plate, and purely for heating purposes, the grate is brought into its lowest position. If, furthermore, the stove is not only to heat its room of installation, but also other rooms as a central heating device, then water-filled traps with forward and return motion junctions are arranged round the combustion chamber, whereby the stove then comprises the boiler of a hot water central heating system. In this case it is a question of a heating stove. The combustion process in continuous combustion and heating stoves must be capable of being regulated in such a way that during certain times of operation, the combustion process elapses only at a very slow rate. This applies particularly for night operation, that is, an operation time during which only a comparatively low level of heating of the installation room or respectively the heating water is required, and when the fuel load in the combustion chamber is to guarantee burning for many hours. This is achieved essentially by bringing the grate into its lowest position, filling the combustion chamber as full as possible with fuel and damping the combustion air supply right down. Very slow burning of the loaded-in fuel supplies is achieved in this way, but only on the condition that a suitable fuel has been used, for example pit coal, coke or briquettes. Slow burning of this type is hard to achieve with other solid fuels, such as peat or wood. The reason for this lies in the different kinematics of carbon combustion with the different solid fuels. Thus, wood, consisting essentially of cellulose and lignin, decomposes, when heated to temperatures between 200 and 300°C, into a plurality of products such as acetic acid, carbolic acid, carbon dioxide and carbon monoxide, some of which have a relatively low ignition point* - 3 51450 Thus, once wood is heated to approximately 300°C, further decomposition and combustion processes become independent, i.e., even when the oxygen supply is interrupted, the decomposition and combustion processes continue independently, and at that in the form of low-temperature carbonisation of the wood, which results in partly-burned waste gases. Therefore, if an attempt is made to operate a continuous combustion or heating stove with wood by placing the maximum amount of wood, corresponding to the size of the combustion chamber, on to the embers, and then damping right down the combustion air supply, then - as opposed to coke, for example - the desired slow burning is not achieved, since the hot waste gases from the embers flow upwards through the pile of wood to the ceiling waste gas aperture, thereby quickly heating the whole load of wood to the said decomposition temperatures, with the result that carbonisation burning of the whole wood pile sets in after a short time. The entire contents of the combustion chamber are thus carbonised or charred in a relatively short time, whereby, furthermore, only partly burnt, smoky and tar-extracting waste gases are produced.

The known continuous combustion and heating stoves therefore can not be operated on wood, peat and similar solid fuels, which of course represent a considerable disadvantage, since in many cases, for example in agriculture, wood and peat are the very fuels which are cheaply available.

The present invention has been developed primarily, though not exclusively, with a view to provide a solid fuel stove which can be operated more hygenically and economically with all types of solid fuel, even wood in particular, with a sufficient capacity for continuous combustion. - 4 51450 According to the invention there is provided a solid fuel stove comprising a housing, a combustion chamber arranged in the housing, charging opening to the combustion chamber, an ashbox located below the combustion chamber, a grate arranged in a lower region of the combustion chamber, an inlet arranged to supply combustion air to the combustion chamber through the grate, an oven compartment arranged in the housing adjacent to the combustion chamber, a hot plate, an upper outlet for exhaust gases arranged in an upper region of the combustion chamber, an additional, lower outlet for exhaust gases tn a side wall of the combustion chamber in a lower region thereof, and exhaust gas ducting communicable with the combustion chamber and arranged so as to be able to convey exhaust gases from the combustion chamber so as to heat the oven compartment and/or the hotplate, the exhaust gas^comprising: an exhaust gas flue, leading from said upper outlet to an exhaust gas stack of the stoye, and branching downstream of the upper outlet into first and second ducts, in which: the first duct runs substantially horizontally oyer the oven compartment and beneath the hotplate, downwards between one stde wall of the housing and one side wall of the oven compartment, substantially horizontally below the oven compartment and subsequently upwards along a rear wall of the housing to the exhaust gas stack; and the second duct first of all runs downwards between the combustion chamber and a further side wall of the oven compartment, substantially horizontally below the floor of the oven compartment and subsequently upwards along the rear wall of the housing to the exhaust gas stack; and in which: the lower outlet is communicable directly with the second duct.; first closing means is provided for controlling the opening and closing of at least said upper outlet thereby to control the supply - 5 50 of exhaust gas from the combustion chamber to the exhaust gas ducting, the closing means in one position allowing communication between the upper outlet and the exhaust gas flue and in another position closing the upper outlet and allowing communication between the lower outlet and the second duct; and second closing means is provided in the exhaust gas flue for controlling the routing of the exhaust gases along the first and/ or second ducts, at least when exhaust gas is supplied to the exhaust gas flue via the upper outlet under the control of the first closing means.

A stove according to the invention, then, has two different waste gas outlets in respect of the combustion chamber. If the upper outlet of the combustion chamber is open, there then results a so-called through-burning, as in traditional stoves, that is, the hot gases from the embers flow upwards through the not yet burning fuel to the ceiling area of the combustion chamber, from where they are discharged from the combustion chamber. This method of operation is suitable for cooking on the hot plate, for roasting in the oven compartment, and for producing intensive heating. If on the other hand, the upper outlet is closing, which can be effected for example by means of a foot-operated pedal or switch projecting out of the stove housing, then the hot gases coming from the embers leave the combustion chamber immediately through the lower outlet adjacent to the grate, with the result that the fuel piled up on the embers which is not yet burning is not penetrated by the hot gases. When wood is used as fuel, a stack of wood piled up on top of the embers is thus not heated to decomposition temperature of the wood, in particular as a result of a counter-current cooling of secondary air passing downwards, and - 6 51450 the pile of fuel remains cool, and only the wood lying directly next to the embers is gradually drawn into the embers.

The result is slow, clean burning with a combustion zone only directly above the grate, as is demanded, for example, for night operation. This type of burning is referred to as underburning, whereby the secondary air has a counter-current cooling effect.

The principle of underburning was, indeed, already known in stoves, that is, in devices, which serve exclusively for the purpose of heating. The stoves operating according to this principle are referred to as continuous combustion stoves or universal continuous combustion stoves. They have a pit-like combustion chamber which can be filled with fuel from above through a loading door situated in the stove top, and have lateral waste gas apertures above the grate; waste gas apei^Jures in the ceiling area of the combusion chamber are not provided. The continuous combustion stoves thus operate exclusively according to the underburning principle and are supplied with fuel from above. Applying this principle, already known in the case of heaters, to stoves appeared up till now to be neither possible nor purposeful, since an essential function of the stove is heating the hot-plate (cooking operation), thus, a function exactly opposed to the method of underburning; even loading fuel from above into the combustion chamber is not usual in the case of a stove, whose hot-plate is of course a cooking point. Only as a result of the development according to the invention has the possibility been created of advantageously applying the underburning principle to stoves, and, what ts more, in a certain combination with the principle of through-burning.

According to preferred developments of the invention, it 1s possible to deal in particular with constructionally simple and easy-to-effect change-over possibilities, such as the achievement of - 7 51450 clean combustion processes in all operational states and as good as possible a matching of the combustion process to heat usage of the waste gases for all operational states, particularly also having regard to the presence of the oven compartment.

One embodiment of stove according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawing in which:Figure 1 is a view in front elevation, and partly in section, of a heating stove with an oven compartment; Figure 2 is a side view, partly in section, seen from the oven side, wherein the oven section is, however, omitted; and Figures 3 to 7 illustrate different modes of operating the stove shown in Figures 1 and 2.

The structure of the heating stove according to the invention will be explained first with reference to Figures 1 and 2.

The heating stove has a complete housing 10 with a hot-plate 10a. The left-hand section of the stove in Figure 1, which Figure 2 shows in lateral elevation, shows the combustion section. It consists of a combustion chamber 11 in the form of an upright pit, an ashbox 12 situated below the combustion chamber and a horizontal grate 13 situated between the combustion chamber 11 and the ashbox 12. The fuel lying on the grate 13 in the form of wooden logs is marked in the drawing with 14. A front loading door 15 permits access to the combustion chamber 11, and a front ash door 16 to the ashbox 12 (Figure 2). The combustion chamber Π and the upper part of the ashbox 12 are surrounded by heat traps 17, which repre-r sent the boiler of a normal hot water central heating system. The cover of the combustion chamber 11 is formed by a fire brick plate 18.

The upper area of the combustion chamber 11 is-connected via - 8 514 5 0 a waste gas aperture 19 to the stove section - on the right in Figure 1 and omitted from Figure 2 - which has an oven compartment 20 and two waste gas ducts 21 and 22. The waste gas duct 21 runs from the waste gas aperture 19 first of all in a horizontal direction between the hot plate 10a and the ceiling of the oven compartment, whereby this section of the duct is marked with 21a, and then vertically downwards between a side wall of the stove housing 10 and a side wall of the oven compartment 20, whereby this section of duct is marked with 21b. From the section of the duct 21b, the path of the waste gas leads on through the horizontal duct section 21c between the oven floor and a double-draw dividing plate 27 and on around the free edge of the double-draw dividing plate 27 to a horizontal duct section 22b below the dividing plate 27 which finally leads between the dividing plate 27 and part of the rear wall of the housing 10 and subsequently between the rear wall of the oven and the rear wall of the housing 10 upwards to the waste gas stacks 24 or 25. In the horizontal duct section 21a is a damper flap 26, which, in the open position, connects the duct section 21a directly to the waste gas aperture 24. The second waste gas duct 22 runs from the waste gas aperture 19 first vertically downwards between a lateral heat trap 17 and a side wall of the oven compartment 20, whereby this section is marked with 22a, then below the horizontal double-draw dividing plate 27, which is situated at a distance below the oyen compartment 20, in a direction to the right (Figure 1), whereby this section is marked in the drawing with 22b, and finally vertically upwards to the waste gas outlet 23. The horizontal duct section 21c between the dividing plate 27 and the floor of the oven compartment 20 is connected on the one hand to the duct section 21b, and on the other hand to the duct 22a and has a baffle plate 28. 29 represents an insulating - 9 51450 cover screening the waste gas aperture 19 adjacent to the oven compartment 20, and 30 represents a heat-insulating plate arranged below the duct section 22b.

The components described up till now correspond to prior art in modern heating stoves, whereas the components described below represent features of the invention.

The combustion chamber 11 is provided in the area directly above the grate 13 with four lateral waste gas apertures 3Λ Situated on the side of the combustion chamber side wall facing the duct section 22a is a sliding pTate 32, which is vertically slidable by means of a rod 33 and an outwardly projecting foot lever 34. In its lower position, shown in Figures 1 and 2, the sliding plate 32 covers the lateral waste gas apertures 31 and leaves the ceiling waste gas aperture 19 free; in its upper position, shown in Figure 2 by a dotted line, the sliding plate 32 leaves the lateral waste gas apertures 31 free and covers the upper waste gas aperture 19. It is also of significance that the combustion chamber 11 is coated with firebricks 35 in the area of the embers. The firebricks 35 have vertical grooves on their rear side, adjacent to the heat traps 17, so that vertical secondary air channels 36 are produced between the firebricks 35 and the heat traps 17, which channels lead upwards from the ash box and are diverted above the ember zone by means of a lowering plate 37 in a downwards direction to the ember zone. Finally, the heating stove also has a damper 38, which is situated in the initial section of the horizontal section of duct 21a adjacent to the waste gas aperture 19 and is operable from the exterior; in Figure 1, the damper 38 is shown in its open position. - 10 51450 The manner of operation of the heating stove is now shown with the use of Figures 3 to 7.

Figure 3 shows the state of the heating stove during the heating-up process. The sliding plate 32 is thereby in its lower position, so that the waste gas aperture 19 is open and the waste gas outlets 31 closed. Both the damper 38 and the damper flap 26 are also open. If the stacked up wood in the combustion chamber 11 is now ignited, combustion air (primary air) flows from the ash box 12 upwards through the grate 13, and the combustion waste gases escape from the upper area of the combustion chamber 11 through the open waste gas aperture 19 into the horizontal duct section 21a, from where they flow through the open damper flap 26 directly into the waste gas outlet 23 and on into the waste gas stack 24. This short waste gas path simplifies and accelerates the heating-up process in a known way. Furthermore, primary air flows out of the ash box 12 upwards through the ducts 36 and after changing direction reaches the combustion area, where the secondary air mixes with the waste gases thereby catering for afterburning. If there is sufficient glow in the wood pile 14 the damper flap 26 is closed, thereby ending the heating-up process.

If the heating stove is to be operated in such a way as to provide cooking and roasting facilities as well as heating the heating water in the heat traps 17, then the heating stove is brought into the position shown in Figure 4. This position differs from the heating-up position only in that the damper flap 26 is closed. The waste gases thus flow out of the upper area of the combustion chamber 11 through the open waste gas aperture 19, whereby, however, the waste gases reaching the ducts 21a - due to the closed damper flap 26 - must now flow downswards first before - 11 they reach the waste gas outlet 23, whereupon they can only travel upwards to the waste gas outlet 23. As a result of the thus increased resistance to flow, part of the waste gases escaping from the aperture 19 is pushed downwards into the duct section 22a, whereby this part of the waste gases then travels underneath the dividing plate 27 due to the counter-pressure of the waste gases arriving from the duct 21b and then flows through a rear aperture of the latter together with the waste gases of the duct 21b upwards to the waste gas outlet 23. When the heating stove is in this position, then, clearly, both the hot-plate 10a is heated to a high temperature, with the result that the whole hot-plate can be used for cooking, and the oven compartment is surrounded on all sides by hot waste gases, whereby high roasting temperatures are obtained.

The heating stove operates according to the so-called through15 burning method, whereby the combustion air flows from below upwards through the fuel and the waste gases flow off upwards. The separately supplied secondary air thereby caters for clean combustion. Fuel consumption and therefore performance with this through-burning method of operation is of course comparatively nigh, i.e. the stove must be topped up freguently.

Figure 5 shows a position of the heating stove which is intended for the case where although intensive heat is to be produced (high output for the hot water), a high temperature for the hot-plate 10a and oven compartment 20 are, however, not required. In this case, the position of Figure 5 differs from that of Figure 4 only in that the damper 38 is pushed downwards, and the waste gas duct 21 therefore closed. The heating stove thus continues to work according to the intensive through-burning process, but the waste gases can only flow through the waste gas duct 22, in other words, in the event of an - 12 51450 intensive heat exchange with the heat trap 17, they flow downwards through the duct section 22a, then underneath the dividing plate 27 through the duct section 22c and finally upwards to the waste gas outlet 23. At all events, in this position, cooking can only be carried out at a low temperature on the area of the hot-plate 10a directly above the combustion chamber, and the temperature in the oven compartment 20 is sufficient only for warming and not for roasting.

There are, however, also times of operation during which neither cooking nor roasting is to be carried out, nor is a high temperature of the hot water in the heat traps 17 required, which is the case, for example, for night-time operation. The position of the heating stove shown in Figure 6 is intended for this type of operation, for example night-time operation. In this case, by pressing down the foot lever 34, the slide-valve damper 32 is pushed upwards, with the result that from then on, the upper waste gas aperture 19 is closed whereas on the other hand the lateral waste gas apertures 31 are open. The damper 38 and damper flap 26 are also closed. In this position, the waste gases no longer flow through the stack of fuel 14, but immediately pass through the waste gas apertures 32 directly above the grate 13 into the lower area of the waste gas duct 22a, from which they flow through the duct 22b out to the waste gas outlet 23. Embers will only form in the area directly above the grate 13, i.e. the heating stove operates according to the principle of so-called underburning. The secondary air, which is also effective here, thereby assists clean combustion.

A very slow burning process is achieved due to the fact that the whole fuel load 14 is not penetrated by the hot waste gases and therefore made to burn through, with the result that, for example, when the stove is full of fuel, even when that fuel is wood, true - 13 51450 continuous combustion is achieved, that is, topping up with fuel during the night for example is not necessary. Therefore, the heating stove filled with wood as a fuel does, however, operate in the manner of coke-fired continuous combustion stoves, i.e. it can burn for several hours with one single fuel load, whereby it affords a comparatively low output for the heating water, but one which is sufficient for night-time operation, for example.

Figure 7 finally shows a position of the heating stove whereby, keeping to the process of underburning in Figure 6, the hot-plate 10a and oven compartment 20 are heated to a certain, albeit a comparatively low temperature. Contrary to the position shown in Figure 6, both the damper 38 and the damper flap 26 are open in this case, with the result that one part of the waste gas escaping from the lateral waste gas apertures 31 flows upwards through the duct section 22a and on through the duct section 21 and the open damper plate 26 to the waste gas stack 24, whilst another part of the waste gas, likewise seeking a short path of flow with low resistance, flows above the dividing plate 27 through the duct 22c and then through the duct 21 upwards to the damper flap 26 and to the waste gas stack 24. Thus, with continual underburning and a low water output, the heat from the waste gases is used, being evenly distributed around the oven compartment, for example for baking at a low temperature.

It arises from the above that a heating stove is created which is able to fulfill several requirements which are completely different in respect of heating technology. It is suitable both for reaching high temperatures for heating water, hot-plate and ovens, whereby it operates according to the through-burning process, and also for maintaining a low temperature for heating (night-time operation) for a long period of time without being topped up with fuel. These -14 51450 advantages can not only be achieved with the usual continuous combustion fuels, such as pit coal and coke, but also with wood, peat and similar materials, which opens up completely new fields of usage for the heating stove, such as in agriculture or in the private sector. Thanks to the favourable secondary air supply, combustion both in the through-burning and underburning processes is very clean and therefore non-polluting, and the danger of tar deposits on the walls of the heat traps to the combustion chamber is considerably reduced by the firebrick coating.

Of course, the stove can undergo numerous modifications.

It is thus possible to provide separate controls for primary air and secondary air, in which case then the secondary air ducts are supplied with air not, for example, from the ash box, but from a separate space, for example the space below the ash box, and separate control organs are provided for the primary air and the secondary air. Also, in place of the fixed grate shown in the drawing, a so-called adjustable grate can be used, whereby the grate position shown in the drawing corresponds to the lowest position of the adjustable grate. It is also possible to design the waste gas route symmetrically, indeed in such a way that lateral waste gas apertures are provided in both opposite side walls of the combustion chamber. It must be said in this context that it is not necessarily essential for the lateral waste gas aperatures to be covered in the through-burning position (waste gas aperture in the ceiling area open); it has been shown in practice that the lateral waste gas apertures, even when they remain open, affect the through-burning only by a small drop in efficiency. Generally speaking, the controlled closing, respectively opening of the waste gas apertures does not have to be effected by means of the slider - 15 51450 shown in the drawing. Thus, it is, for example, also possible to place the cover 18 of the combustion chamber only loosely on to the side walls and to provide a mechanism by means of which the cover can be raised, thus creating a waste gas aperture. Parti5 cularly advantageous is a design of a type whereby the upper edges of the side walls slope, and whereby then the cover also lies at an angle on the side walls and, to open the waste gas aperture, is only raised on the lower side, perhaps with a hook, which is mechanically connected to the slider for the lateral waste gas apertures.

In place of the slider 32 and the damper 38, a single flap element can be provided, which can adopt three positions and therefore substantially carry out the functions of the slider 32 and damper 38. This single element cannot exactly duplicate the functions of the two separate closure elements. However, in practice, it is not essential for the lower outlet 31 to be closed whenever the upper outlet 19 is open, since most of the exhaust gases will tend to flow upwardly to the upper outlet to be discharged from the combustion chamber via the upper outlet. There20 fore, in practice, a single flap arrangement can duplicate the functions of the slider 32 and damper 38.

It will be evident from the preceding description of the preferred embodiment of the invention that there is provided a solid fuel stove which has exhaust gas ducting (21, 22) communicable with the combustion chamber (11) and arranged so as to be able to convey exhaust gases from the combustion chamber so as to heat the oven compartment (20) and/or the hot plate (10a). The exhaust gas ducting comprises an exhaust gas flue (21,22), leading from the - 16 51450 upper outlet (19) of the combustion chamber to an exhaust gas stack (24) of the stove, the flue branching downstream of the upper outlet (19) into a first duct (21a, b, c) and a second duct (22a, b).

The first duct (21a, b, c) runs substantially horizontally over the oven compartment and beneath the hot plate, downwards between one side wall of the housing and one sidewall of the oven compartment, substantially horizontally below the oven compartment and subsequently upwards along a rear wall of the housing to the exhaust gas stack.

The second duct (22a, b) first of all runs downwards between the combustion chamber and a further side wall of the oven compartment, substantially horizontally below the floor of the oven compartment and subsequently upwards along the rear wall of the housing to the exhaust gas stack.

The upper outlet (19) of the combustion chamber is communicable directly with the exhaust gas flue (21, 22), whereas the lower outlet (31) is communicable directly with the second duct (22a, b).

The slide plate (32) forms a first closing means for controlling the supply of exhaust gas from the combustion chamber (11) to the exhaust gas ducting (21, 22), the closing means in one mode allowing communication between the upper outlet (19) and the exhaust gas flue (21,22) and in another mode allowing communication between the lower outlet (31) and the second duct (22a, b).

The damper (38) forms second closing means which is provided for controlling the routing of the exhaust gases along the first duct (21a, b, c) and/or the second duct (22a, b), when exhaust gas is supplied to the second duct via the lower outlet (31) or to the - 17 S1450 exhaust gas flue (21, 22) via the upper outlet (19) under the control of the first closing means (32).

The different possibilities for routing the exhaust gases along the first and second ducts, upon appropriate operation of the first and second closing means (32, 38) has been described above with reference to Figures 3 to 7. - 18 51450

Claims (10)

1. A solid fuel stove comprising a housing, a combustion chamber arranged in the housing, a charging opening to the combustion chamber, an ashbox located below the combustion chamber, a grate arranged in a lower region of the combustion chamber, an inlet arranged to supply combustion air to the combustion chamber through the grate, an oven compartment arranged in the housing adjacent to the combustion chamber, a hot plate, an upper outlet for exhaust gases arranged in an upper region of the combustion chamber, an additional, lower outlet for exhaust gases in a side wall of the combustion chamber in a lower region thereof, and exhaust gas ducting communicable with the combustion chamber and arranged so as to be able to convey exhaust gases from the combustion chamber so as to heat the oven compartment and/or the hotplate, the exhaust gas ducting comprising: an exhaust gas flue, leading from said upper outlet to an exhaust gas stack of the stove, and branching downstream of the upper outlet into first and second ducts, in which: the first duct runs substantially horizontally over the oven compartment and beneath the hotplate, downwards between one side wall of the housing and one side wall of the oven compartment, substantially horizontally below the oven compartment and subsequently upwards along a rear wall of the housing to the exhaust gas stack; and the second duct first of all runs downwards between the combustion chamber and a further side wall of the oven compartment and subsequently upwards along the rear wall of the housing to the - 19 exhaust gas stack; and in which: the lower outlet is communicable directly with the second duct; first closing means is provided for controlling the opening 5 and closing of at least said upper outlet and thereby to control the supply of exhaust gas from the combustion chamber to the exhaust gas ducting, the closing means in one position allowing communication between the upper outlet and the exhaust gas flue and in another position closing the upper outlet and allowing 10 communication between the lower outlet and the second duct; and second closing means is provided in the exhaust gas flue for controlling the routing of the exhaust gases along the first and/or second ducts, at least when exhaust gas is supplied to the exhaust gas flue via the upper outlet under the control of the 15 first closing means.

2. A stove according to claim 1, in which the first closing means is arranged to operate so that, when the upper outlet is open the lower outlet is always closed, and when the upper outlet is closed the lower outlet is always open, said first closing 20 means having an operating element in the form of a handle or foot pedal projecting out of the stove housing.

3. A stove according to claim 1 or 2, including a heightadjustable grate, in which the lower outlet comprises side wall exhaust gas apertures arranged in a region of the combustion chamber 25 directly above the grate when the latter is in its lowest position.

4. A stove according to any one of the preceding claims, including combustion air ducts for providing secondary air separately from the supply of primary combustion air, which ducts lead to the - 20 514 5 0 upper region of the combustion chamber so as to open out above a fuel load on the grate.

5. A stove according to claim 4, including means for controlling the flow of secondary air through said separate air ducts.

6. A stove according to claim 5, in which said separate air ducts originate from a chamber separate from the ashbox.

7. A stove according to any one of the preceding claims, in which the side walls of the combustion chamber are coated with fire-bricks.

8. A stove according to claim 7, in which secondary air channels run through said fire-bricks.

9. A stove according to any one of the preceding claims, in which the said first exhaust gas duct runs substantially horizontally over the oven compartment, then downwards between one side wall of the housing and one side wall of the oven compartment, then substantially horizontally between the oven floor and a double-draw dividing plate, round the latter and then under the dividing plate, whereupon it finally leads upwards between the dividing plate and part of the rear wall of the housing to the exhaust gas stack, whilst the second duct first of all runs downwards between the combustion chamber and the wen, then substantially horizontally below the double-draw dividing plate and subseguently upwards between the dividing plate and part of the rear housing wall to the exhaust gas stack. 11. A stove according to any one of the preceding claims, in which the first closing means comprises a slide plate which is movable between a lower position in which it opens the upper outlet - 21 51450 and closes the lower outlet and an upper position in which it closes the upper outlet and opens the lower outlet, and in which the second closing means comprises a damper arranged adjacent to the branching of the first and second ducts. 5 12. A stove according to claim 1, in which the first and second closing means are formed by a single flap element which is movable to control the opening and closing of the upper outlet, and to control the routing of exhaust gas therefrom along the first and/or second ducts.

10. 13. A stove according to claim 1 and substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings. Dated this 29 day of June 1981 BY: TOMKINS & CO AjSplXcants' Agents SIGNED: 5 Dartmouth Roaa DUBLIN 6 - 22 sheet 1 WAMSLER HERD-UND OFEN GmbH