I'm with the no heat crowd. Unless you have some kind of thinly feathered exotic breed, they need no help from us to stay warm. I have an open-air, un-insulated coop. The whole front wall is just hardware cloth. We've had winter temps down to -10F, not including any windchill, and none of my birds have ever suffered frostbite. And some of them have tall combs. None of them have had any problems. You have to really get into the negatives, for them to get frostbit. And if they do get it (Above those low negative temps), it more than likely your fault. Either from overcrowding, insufficient ventilation, or a combo of both.
Putting a heatlamp in there, is a total waste of time and money. The only thing it's good for, is for burning the coop down, and leaving you with fried chicken. We have already seen one post, where somebody burned their coop down, in some inane attempt to "KeepThemWarm". Well, they accomplished that, plus some. And I'm sure that won't be the last such story, we see this year.