Twice this week my chickens roosted high up in a tree and I could Not get them down. a few were in the coop,so I couldnt leave the coop door open, for fear of predators. So they stayed up there all night. One night it went down to 16F and the other night down to 11F !
I do think the rooster got some frostbite on his comb. Other than that everyone was fine. I noticed their feathers seemed to surround the branch and completely coverred their toes. all toes are fine.
I know there are folks around here who have basically No coops for their chickens. They insist they have lost none to cold (plenty to predators apparently)
So while I work to make my coop draft free and well insulated, I am more concerned about moisture than heat. I know they are better off "underheated" than overheated.
Oh I have cheap plastic waterers that hold about a gallon. I heat rocks and put them In the water and it keeps it liquid for several additional hrs in the night. In the day I do the same and have the water in a little "sunroom" off the south side of the coop, which on sunny days ( which are few) helps considerably.
You have to be careful heating rocks. Granite heated on the woodstove has been fine for me. certain rocks can explode when heated so don't try this unless you know what you are doing. I would like to heat them in the microwave, but I don't understand the risks. if anyone happens to know, I'd love to learn.
Great idea.