Should I heat my coop?
This question echos throughout the threads of BYC ever fall and early winter. This article addresses the tale of how one VermontGal resolved this question. I also endeavor to provide you with some information about chicken's environmental needs, coop construction & insulation, and other considerations in coop heating.

Throughout the article, temperatures are in Fahrenheit; I will add Celsius later as time permits.

In 2008, I finally got my long-awaited chickens -- a small flock of 4 pullets, well-suited to my urban backyard. I built them a chicken tractor over the summer, and then set about making a chicken coop in a corner of my barn for the winter. As this was a winter coop, I knew I wanted to insulate it against the northern Vermont winters, which typically include a few nights around -25°F. Using my knowledge of home construction, I built a coop that paid attention to air sealing and insulation. Controversially, I do heat the coop, but only on very cold nights. Based on careful temperature observations, I heat my coop only when the outside temperature is below -10°F. Several factors have gone into that decision, and I invite you to read on about how I reached this conclusion.

Chickens have built-in down coats and, like other birds, puff themselves up in cold weather to maximize the insulative value of the feathers. Just as human beings like temperatures best in the 70s, but are completely good with heating a winter home to temperatures in the 60s (put on a sweater) -- chickens prefer temperatures in the 40s or higher, but are cold-hardy to temperatures at least in the teens. Gail Damerow's Guide to Raising Chickens reference 45°F as the temperature beyond which egg production may drop. I am skeptical. While commercial hatcheries (with plenty of chicken heat from the birds themselves in massive poultry barns) may report this, most backyard chicken flock owners report birds laying an egg a day in temperatures well below freezing. Much bigger factors are the age of the bird, and the amount of light.

Chicken Breed: How cold hardy your chicken is will partly depend on the breed of chicken. Generally, larger chickens are more cold hardy, mostly as a matter of their own body heat. Larger birds make more heat with their own living flesh. However, some smaller chickens are also cold hardy. I have never seen a list that identifies chickens' cold hardiness by temperature numbers. A good list of general cold hardiness is included (LINK to Ithaca).

Combs: A second major question is the type of comb on your chickens. Pea combs, rose combs, and walnut-combs, all nestled close to the head, are able to withstand lower temperatures. Single combs and other erect combs may suffer from frostbite. Most people report that frostbite is of biggest concern to roosters (with larger combs). Hens that have very large combs, such as leghorns, are also of concern. As a result of comb vulnerability, these chickens are not considered cold hardy. The wattles and feet also need to be protected from frostbite. However, the chicken can tuck her feet into her downy breast when she is sitting on the roost; and she scrunches her neck down so that her waddles are covered by her upper breast/neck feathers.
Several people in the Backyard Chicken forum have said that they are most concerned about frostbite when coop temperatures reach below 20°F. Rubbing petroleum jelly on the comb may help to prevent frostbite, through both the protective layer of oil and through the comb-massage stimulating blood circulation as you apply the jelly. The controversial process called dubbing protects birds from frostbite by preventatively cutting off the combs.
In hindsight, living in Vermont, I wish I had known more about chicken hardiness, especially with regard to combs. I have three single-comb chickens, and I worry. My one Easter Egger (a mistake at the feedstore, as I wanted a Rhode Island Red) has a pea comb. When I next buy chickens, I may get pea-combed Wyandottes instead of single-combed Plymouth Rocks, for example.

In making my decisions about heating and insulation, one important factor was the fact that I only have 4 chickens. Chickens put off a good amount of body heat, and many people who have uninsulated chicken coops in my climate have backyard flocks of 10-25 chickens. If you have only a few chickens, your birds will need more help in dealing with the cold. Chickens huddle together on the roost, and the body heat from 25 heavy-breed chickens is like having a 400-watt heater in your coop! If you want to figure out how much "chicken heat" your coop has - multiply the weight of your chickens in pounds *8 BTUs. For example, my pullets weigh approximately 6 lbs each. 6 lbs x 4 birds = 24 lbs for the flock.

*8 BTUs per hour per pound. If my chickens weigh ~6 lbs each on average, then the 4 chickens put out 192 BTUs per hour, which is about the same as a 56 watt heater.

In selecting your chickens, did you choose breeds that are listed as cold hardy? (reference link). Larger birds tend to be more cold hardy. Again, the body heat from their own body mass is a factor in keeping them warm. Another primary consideration is what type of comb and wattles do your chickens have? A single comb chicken is more susceptible to frostbite on the comb. Roosters' larger combs are more susceptible than hens'. Chickens with combs that lie close to the head are less likely to get frostbite.

Further reading:
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