I have a small chicken coop with three chickens in it in my backyard. Today, when i went to feed them this morning I looked inside the coop and noticed small ice crystals formed on the walls and ceiling of the coop. The temprature did drop to -11 last night, but they seemed just fine, maybe a little aggitated, but other then that fine. Does this mean that my coop is not draft free or is too cold? Will this hurt my chickens?