The two things that plagued my Cold House mind most, last winter, were the heat lost from hot showering/bathing/dishwashing/clothes-washing water, and the heat lost from the clothes dryer.
I (crudely) addressed the first issue by keeping the shower water in the freestanding iron tub till it got cold, and collecting the hot dishwasher/washing machine discharge in 10-gallon pails (keeping them until cold.) The new house doesn’t have such a convenient tub; it’s built-in, and against an outside wall, so getting water heat back through it will be less efficient. However, I have schemes in mind for rigging up a full graywater heat reclamation system (it involves a couple of 55 gallon steel drums, if I can find such.)
The dryer issue, however, remains problematic. Some propose that you can “reclaim” the heat from your dryer simply by venting the dryer into your house, instead of outdoors. There are even commercial gizmos such as this one for the purpose. Since the dryer exhaust is hot, it seems intuitive that diverting it to stay inside the house would allow you to reclaim the heat. Unfortunate it’s not really that simple– because the vast majority of the heat of the dryer exhaust is contained in gaseous water, not in the air. If you
redirect that into the house, the water vapor quickly condenses to liquid water, probably mostly on your windows and cellar floor. That gives off heat, indeed. But then it will again eventually re-evaporate, taking with it the same amount of heat you “reclaimed”. (If it doesn’t eventually re-evaporate, perhaps because your house is incredibly well-sealed, then you will wind up with a warmer but sopping wet house.)
Anyway, the only way to really get the heat back from dryer exhaust is to condense the water contained within it, and then dispose of that water before it evaporates again. Not easy to do. Last winter I experimented with counter-current condensers, in which a six-foot aluminum pipe carrying the dryer exhaust ran inside a larger-diameter aluminum pipe carrying the dryer intake air (the theory being that the water in the exhaust would condense, and drip out the far end.) But it was a miserable failure– only about a tablespoon of the 1+ gallons of water actually condensed. The moral: you need a huge amount of concentrated coldness to absorb the amount of rapid heat produced by the dryer evaporation.
The closest I came to success was by using another electrical appliance to suck up and spit back the heat of the first. By directing the dryer exhaust through a dehumidifier, I managed to condense about 80% of the evaporated water in real-time. This was pretty promising. The dehumidifier, of course, used some additional electricity of its own; but used in this fashion, it spits back much more heat than its own electric draw. The primary problems with this set-up were (1) no matter what I did with filters, lint started to clog the dehumidifier; and (2) there was too much technology, and too many moving parts.
All summer (while we’ve been using a clothes line, mostly) I’ve been wracking my brain for a better way to get condense the dryer vent moisture and get back that heat. But I haven’t come up with one that is cheap and both thermodynamically and functionally practical.