I'm not going to worry about the temperature in my two coops during the winter because I have insulated all the walls with rolls of housing insulation, put in double-pane windows, and made sure that there's no place a draft can come in. The edges of the ceiling will provide ventilation to expel excess humidity given off by the chickens and possible gasses from damp bedding/poo. My roosts are all 2x4's turned so that the chickens can sit/squat on the 3 1/2-inch side and keep their toes from freezing with their feathers.
These are birds, and like any other bird, they're designed with feather insulation to live through the coldest of weather. The way I see it is that if the birds out in the trees are alright, then it's for darn sure that the birds in my coops are A-okay as long as they have lots of food to keep up their energy/body heat and fresh water. My waterer will be heated though so that they will always have it available without my having to make several daily trips out to replace frozen water; after all, I want to stay in where I'm comfortable too.
I agree Joe. A hardy vigorous flock should be able to withstand the environment they live in. If they can't, they shouldn't be there. Chickens acclimate well if given the opportunity and planned correctly. I do not supplement heat in my chicken houses unless I have babies in them. Adult chickens use their plumage to regulate their own body temperatures.
I have wild eastern turkeys who live outside all winter with no shelter. If they can withstand it outdoors, the chickens can in their coops with shelter from the weather. Personally, I feel if you supplement it weakens the birds and puts them at risk (especially for times when heat cannot be provided, like a power outage).
Well, I must be the only softie who supplements with heat lamps.
When the wind chill here in Ohio is at zero degrees, I sleep better knowing that my chickens aren't suffering, or, worse, freezing to death. I only turn on one lamp when the temps get down in the low twenties or below, and when the wind chill is really bad, I use both lamps to keep the temps right around freezing (not only for the hens, but also for their water). It's certainly not what I'd call cozy in the coop when it's hovering at 30 degrees, but it keeps them alive, and that's what matters to me.
I have a couple very old hens (14 years), so I do give them a lamp on nights that are 20 or below. My chickens are still hearty-coop was less than desirable last winter, not at all draft free, and nochickie died. I like to keep them from freezing, yet not pamper them.
This year, I have newly hatched chicks coming at the beginning of October, and they will be in part of the coop by 1 month I hope. I plan to make this part as draft free as possible, with a bit of ventilation at the top, and they will have a heat lamp.
My point wasn't to say that providing heat is wrong. Folks will do what they desire and it is human desire, not chicken necessity on who will or will not provide heat for their birds. (with the exception of extreme cold climates like in Alaska and Canada) I think saying that a fully feathered bird is suffering because they don't have a heat lamp is a bit over the top. My birds do not suffer all winter long. They are in a protective shelter. They are hardy and vigorous and correctly acclimated to their climate, which is why they thrive so well here. I have never had a chicken freeze to death.
Personally where I live I feel that giving the birds in my coop artificial heat would be wrong. My goal is to allow the girls to acclimate to their surroundings. Living in cold weather climates, the birds will grow extra down, learn how to fluff and as long as you have a perch that is large enough so the girls can drop their feathers over that middle longer toe. If they cannot, then that toe will be to cold and freeze.
Also deep litter method is the best for winter, it produces its own "composting" heat. May not feel like much to us.
As an example, you have that heat lamp so your coop is a nice even 60 degrees, nice...and then a snow storm comes in, takes lines down with it, you have no electricity. Hmmm, what happens to your chickens? You can bring them in the house, but your not going to have heat either unless you have a generator etc etc.
Don't start something that you may have to be very concerned about later when its taken away.