Image courtesy wood-stoves.org
An oft-debated topic among chicken keepers is the subject of heating your coop or not.
Some well-known chicken experts flat out say no - never, ever heat your coop. Their rationale is that people have been raising chickens forever, even before electricity was invented, so chickens don't need heat. I don't agree with that completely.
Image courtesy mary jane's farm magazine
Remember, generations ago, not only did chickens most likely sleep right in the barn along with the other animals, maybe even snuggled up next to a fuzzy sheep or roosting on the rafters above a pen full of warm cows, but back then people only had breeds that were indigenous to their particular climate. They weren't ordering fancy breeds from a breeder or getting a box of chicks delivered by their mail carrier!
They had Rhode Island Reds, Plymouth Rocks, Buff Orpingtons, Wyandottes, and other cold-hardy breeds that they bought at their local feed store. And the average farmer had alot more than 4 or 5 chickens snuggling together on a roost trying to stay warm.
Chicken raising has evolved in just a few generations to be something entirely different. Backyard coops are springing up everywhere, housing just a few chickens, sometimes chosen not for their cold-hardiness but for temperament, appearance or egg color. There's nothing wrong with that, but you need to be aware of how your flock will do in the cold and make allowances.
I agree in principle that heating your coop isn't a good idea because of the fire hazard and because your chickens will be alot more hardy and healthy if they gradually get used to the drop in temperature. Also, chickens are actually pretty cold-hardy and know to fluff their feathers to trap warm air next to their bodies. They have a much harder time in the heat than in the cold, being most comfortable in temperatures between 40-70 degrees F.
If your chickens rely on the heat, in addition to the fire hazard that any heat source poses, if you were to ever lose power or the bulb burn out, your chickens could die, not used to being without heat. In addition, the difference in temps between night (warm) and day (cold) isn't good for them and the heat will create moisture, which can lead to frostbite. Natural is usually better when it comes to most animal care.
However, use your best judgement and remember there ARE situations when heat might not be a bad idea:
1) if the temperature is predicted to suddenly drop 20+ degrees from the norm,
2) if you have young chicks who are going from indoors to outside during the winter or pullets that are not fully grown,
3) if you have chickens who are injured or recovering from a sickness,
4) if you only have two or three hens in a large coop so their body heat won't be sufficient to keep them warm,
5) if you have breeds that are not cold-hardy, such as silkies, polish and frizzles.
A friend of mine lost her silkies last winter to the cold after reading on another chicken page that chickens NEVER need a heated coop. I just read a post from someone else yesterday about losing a silkie to the cold because she didn't realize that silkies can't fluff their feathers to stay warm like other breeds. Another friend had to have her rooster's foot amputated because of frostbite. It's important to make your decision based on your location, situation and mix of breeds.
If you DO decide to provide a heat source, be sure it is secured so nothing can catch on fire... and then secure it again. Remember that clamps can come unscrewed, wires untwisted and bulbs will shatter if water hits them. Use caution and common sense and you should be fine.
All that said, a well-insulated, -ventilated (but not drafty), dry coop IS the preferred solution. A thick straw floor cover, straw bales along the outer walls, using the deep litter method (basically maintaining a 12" floor base of straw, and turning it over periodically to let the poop decompose and create heat), having the correct number of hens for the size of the coop and giving your girls scratch just before bedtime are all inexpensive ways to keep your coop warm. Even snow is a wonderful insulator, believe it or not. Think igloos...
But of course the best way to keep your chickens warm in the winter is to get MORE chickens ! An average-sized chicken produces about 40 BTUs of heat. With my 21 chickens snuggled in my coop each night, it has been consistently averaging 9 degrees higher than the outside temperature when I open it up in the morning, due entirely to the chickens' body heat and the heat created by using the deep litter method.