Older homes often lack bathroom exhaust fans. In the old days, if the bathroom was smelly or steamy, you were supposed to open a window to air it out. This isn’t a very logical ventilation method, especially when temperatures are below zero, or when the weather is 90°F and humid. Yet this time-honored method of bathroom ventilation is still enshrined in our building codes. According to the 2009 International Residential Code (sections R303.3 and M1507.3), a bathroom with an operable window...