I live in Eastern Oregon. It's been getting down in the teens at night and will do so over the rest of the winter. I have 6 hens who pile on top of each other in their coop, I think they stay warm enough but not for sure? Their coop is about 3' Tall 4' Wide and 4' Long. They have tons of hay in there too. I worry so much about them staying warm enough without heat lamps. My husband says it would be silly to put a heat lamp in there! Any info on this would be appreciated. P.S. The one hen I worry most about is a very small, lean Australorp (?), but she is always at the bottom on the hen pile when they sleep.