O and I just saw on another thread, not to bring your chickens inside if they have frostbite. It actually will open them to infection. I didn't know that. Handy piece of info
I do agree with that to an extent, because when they just have a few comb tips darkening, it doesn't seem like enough of an issue. However, when their comb and wattles are blue and swollen, I believe it's best to get them into the warmth to prevent further damage. Two of my girls, Rangi and Olive, had swollen wattles after that first bout of subzero temps at the beginning of the month and it took them several days inside before the swelling even reduced. They are now in the process of losing big portions of their wattles and the tips off of their combs, but they could have been much worse off if I had left them outside to tough through it. That's my policy. If you're really more worried about infection than frostbite damage in this case, then get some Neosporin to put on their combs and wattles while they're inside.
This should
not be confused with justifying heating the coop, as
adding heat to the coop can actually make frostbite worse by allowing moisture to stay in the cold air. Moisture in combination with cold is what causes frostbite, not just the cold itself. If you're seeing frostbite in your birds as I did, then that should tell you that you need to work on your winter ventilation. Remember, as long as it's not blowing directly at the birds while they roost, it can be a safe and effective source of ventilation in the wintertime.
As a side note, when you bring a bird into the house,
you need to be prepared for them to stay in the house until it's at least warm enough that it won't be a shock to put them back outside. Rangi and Olive went back outside in that weekend of 40's we had just after those two days of subzero temps and they are doing fine now. I currently have a little banty, Rose, inside because she's been sick and it looks like now that she's better, she won't be going back outside for a long time. :/ Oh, well. Rosie's living the high life right now, although I can tell she misses her flock.