Yes, I understand that humidity is a factor. I have a few more chickens than I "should" in my coop, although there is no fighting, and there are no signs of poor health. It is clean and well ventilated. I have decided to redesign next spring, and I am considering an open front, three sided coop. Assuming maximum ventilation is occurring, how cold can chickens tolerate before combs get frostbitten? I have a couple that insist on roosting out in their run at night, and we've been getting into the low 20's. I usually move them into the coop when I check on them before bed. They seem fine, and aren't even huddled together. They're toasty as can be under those feathers.