My practice room is a "basement" room that has no heating or air ducts. It's not actually undergound, though, so it doesn't benefit from any of the insulating properties of a true cellar.
I live in a warm climate. In the summer the temperature is not really a problem -- enough air-conditioned air migrates downstairs to keep the temperature below 80 degrees farenheit. But in winter, the temperature in the room can dip to the mid-60s, which is too cold for me to practice comfortably. So, I run a small space heater down there when necessary.
My question is, can a relatively rapid change in temperature from the mid-60s to the mid-70s harm my guitars. I know you shouldn't store a guitar in extreme cold or extreme heat, or move them rapidly from one extreme to the other. But these are relatively moderate temperatures, and the change is not as abrupt as, say, moving the guitar from indoors to an extremely hot or extremely cold vehicle.
Should I worry about this?
BTW, I know a space heater can also dry out a room, too. But I've noticed from watching the hydrometer that it the humidity goes down a lot slower than the temperature goes up -- and I do keep the case humidified.