Our normal winter low is about 26 but most nights 36 or above....we had temps to 4-5 degrees at night with daytime of 12 in early Dec....temps had been 40 at night prior so no adjustment.....got some doghouses of craigs list....the chickens pile in on top of each other inside the coop on real cold nights....they all survived the cold....had 2 inside died...had gotten wet(tried to swim in their water) then power went out and they were still under lamps the week before...so heat lamps would not work for us in cold....we lose out electicity with that. I did have one with frostbite on her foot, but she is recovering nicely.....laid eggs all but the first few days!