Chickens and cold
You don't have to heat the chicken coop but I'd make sure it's dry and free of drafts. I string some Christmas lights on the coop in winter which makes it easy to collect eggs in the dark and seems to keep the egg production up. I keep their water thawed with a base under the metal waterer that has a 40 watt incandescent bulb, and lug a bucket of hot water out in the morning too. Birds with large combs or wattles, especially roosters, can get frost bite there below about 0F without supplemental heat. Also, if you can't collect eggs until late in the day, they can freeze and crack if the coop is really cold.
I have to deal with really poor circulation and freezing in my hands in winter. One of the best investments I made to be able to enjoy the outdoors was in a pair of mountain/expedition mittens like they climb Everest with, plus a large supply of hand warmer packets.