I wish more of these postings included the lowest INTERIOR TEMP OF THE COOP you have experienced, or the interior temp when frostbite happened. That would be most helpful. I know humidity is a main factor, but how cold is too cold? And why not some hygrometer readings as well, if that is really the issue? It is is all so imprecise, and I know much of it must remain so, but any way that we can get more numbers would be great.
I had a dutch bantam and a sebright bantam in a hen house when the temps got down to -10 or worse outside at night a couple of winters ago, and the dutch got frostbitten comb. I did not have a thermometer in the henhouse then like I do now. There were no drafts, but maybe they were just too small to keep warm enough at that temp with just two of them. And I tell you, that hen, always super-friendly before, was really ticked off at me for some time after that! Scolded and pecked me whenever I reached in.
On another note, someone posted this:
Something I just learned today about water: Cold water takes longer to freeze.
So, if you put boiling hot water outside it will freeze faster than lukewarm water.
I am SO TIRED of people saying things like this this and not knowing what it means, thereby confusing other people ad infinitum. The time something takes to happen, and the rate at which it happens, are different things. (Think about the time it takes to drive someplace, versus the speed [rate] at which you will need to drive.) So, here's the deal.... If you have identical containers, one with cold water and one with hot water, under identical frigid conditions, the cold water will freeze first. Cold water does not take LONGER to freeze. It cools at a slower RATE , because the temperature differential is not so great. The RATE (speed) at which the cooling happens is greater for the hot water. Still, the cooling is NOT fast enough that the hot water catches up with the cold water and freezes first.