Maybe you can help. How many chickens do you have? I'm in PA and my husband and I have been disagreeing on heating the coop. Like you, we've seen close to -20F here, but VERY rarely. We have 14 hens and one roo: 3 americaunas, 3 amberlinks, 3 RIRs, 2 Ply barred Rocks and and Americauna roo. The other issue is regarding the feather-plucking that has been happening. We've tried EVERYTHING to address the 3 bullies, but nothing has helped. I cannot even recommend the blinders. We have used "pick-no-more" with zero success. In other words, we have some hens that are missing feathers on their heads, but mostly at the base of their tails. Some of the patches are 1.5" x 3" ! Even our roo has some missing feathers under his wings, and his tail is a mess. We've gone back to feeding starter feed for the added protein (22%).
Bottom line, the question for you is, with missing feathers and only 15 birds, is it still ok to leave them w/o heat? Our coop is NOT insulated. It is dry, not drafty and closes up fairly tight at night, even when it's windy out. We keep it relatively clean and yes, the girls still free-range for about 1.5 hours each evening, rain, snow or sun.
Thanks for any advice! Merry Christmas!