Its -8f, windchill-20, and it is 30 inside coop, water is still not frozen, nice and dry inside. I have a 600 watt oil rad hater on low, and a brooder heat light over the water area, humidity is 50%. Birds all seem happy, being little Bantams, might be happier thanif it were 0 inside, with water not frozen, this takes the edge off for them...