Chickens heat themselves, they have a wonderful coat of down which they can fluff up and hold a cushion of heat next to their bodies, if it's colder hens will sit next to each other, supplemental heat isn't necessary, south facing windows are welcome on cold days and chickens will gather in the sunlight, feeding a chicken more complex foods in the winter like whole corn and sunflower seeds can help create more internal heating through digestion. Also giving them slabs of hay will keep them moving and busy. Chickens don't seem bothered by the temperature until it's well below zero, -20 or less, and when weather initially drops suddenly, today it was 30's, my poultry looks cold, in a month or two 30 will be a nice warm day, acclamation, without it they are cold all winter.
You can use heat, many do mostly because of guilt, but it's unnecessary in most instances, we all do things differently, good luck with whatever you decide.