When people like I say I heat my coop, those who don't understand think they live in a sauna of sorts, where it's the same temp as in my house. There is one person I know who does that but they're in their 80's and want to spend time in the coop without dying in there themselves.
As I stated above several days ago, I and many others, due to temps or types of birds, or personal preference of not wanting frozen eggs or water, we heat to keep the coop from freezing so around 35-40F. If power goes out, the water and eggs freezing is my only worry. If the temps outside are sub-zero, we'd run the generator.