Where It’s At
During primary and secondary fermentation I keep the beer in a closet on the main floor of our house. As the closet is an interior one, the temperature is relatively stable. It’s important that it’s on the main floor since this is the only level of our house we keep at a relatively decent room temperature (good ale temp). I keep the door open a crack (at least during primary), however, because the closet tends to get colder than the room, which is likely due to the colder temperatures of the floors above (cool second story in winter) and below (cellar/basement). The potential problem I can see with cracking the door is light infiltration, but the fermenters are pretty well covered, and I keep the blinds closed to keep the room pretty dark most of the time.
We had a cold snap (for western Oregon) during my latest primary fermentation, so I put a little thermostat-controlled space heater in the room, as we let the house get colder at night. I won’t normally do this, but the house was cooling fast at night and it was right at the start of primary, so I didn’t want to give the yeast that adversity.
The beer does seem to hold steady at about 64 to 65 degrees F, which is within the 60-75 range recommended. One of these days I might build a short platform for the fermenter(s) so I can have a free-convection air barrier between the bottom of the fermenter and the cold-ish floor. Right now the beer just sits on a layer of towels on top of the carpet.