I'm telling you to pull the heat source because they don't need it and it's a fire hazard. Additionally, it keeps them from properly acclimating to their environment. Another risk is if you suddenly lose power and they are plunged into much colder temperatures than they've grown accustomed to. There are very few situations in which supplemental heat is required for keeping chickens alive and healthy during winter.
My flock has been exposed to temperatures as low as -23F and they've been just fine. The only bird that had any frostbite was my rooster with a large single comb and he had mild frostbite dubbing.
A lot of people forget that birds are not mammals. They come equipped with down feathers, a high body temperature and the ability to fluff their outer feathers to trap in their body heat. That is why ventilation is so critical for birds. Not only do they have delicate respiratory systems but the moist air that they breathe out needs to be able to rise and escape and be exchanged with dry fresh air.
This is my uninsulated, unheated coop with approximately 17 sq ft of ventilation both high and low on a January morning that was 9°.
Notice that several of the birds up on the boards and roosts as well as down on the floor are all fluffed up. Keeping warm.
