My chickens haven't had any problems with staying warm in the winter. I never supplement heat in the winter. I also let mine out every day to the free range fenced in area, they have zero issues with the cold.
I think we as humans feel cold so we feel like the chickens are cold. Animals are well-equipped to handle colder weather than we are.
Yeah, mine are out and about everyday....unless there is fresh snow I haven't shoveled paths through yet.