I have mine is set to come on at 10 and off at 20 degrees. The chickens are fine in there... Its me that worries. I went back and forth for quite awhile as to will i or wont i put a heat source in the coop. Well,,, when it got to be 10 degrees and colder, my heart won out over my head. They are pretty snuggly in the coop with lots of extra hay. They seem to still prefer the roost, and I nevver even saw them actually sit under it.... I watch the chick-a-dees from my window and remember they dont have heat, or a nice coop either.....