With many instances of chicken coop fires in the news recently, such as this one that caused $35,000 in damages, it is only natural to wonder whether or not adding additional heat sources to your coop is safe or necessary. No one wants to risk injury to their chickens by burns or fires, but how can you ensure that your chickens stay warm enough in the winter months? Heat lamps are commonly implored as warming devices, but they are also responsible for many of the fires reported every year, fires that can claim your chickens and their coop. If those fires are unnoticed and go unchecked, they can also grow large enough can consume your barn and possibly home as well. There are serious dangers associated with heat lamps that should be strongly considered before attempting to use one.
Chickens themselves are a good source of heat. In fact, one laying hen weighing in at approximately 5lbs is able to generate close to 10 watts of heat all on her own. With this in mind, if you have a coop with ten of these hens, you already have the same heat output as a 100 watt light bulb. One way to add more heat to your coop is to simply add more chickens. This works in much the same way is if you were to enter a cold movie theater alone. By yourself you will be cold, but as movie time grows nearer and people start to pile in, the room temperature goes up because of body heat. Chicken body heat works the same way.
You can also increase heat maintenance and production in your coop by adding windows. As sunlight streams through windows, it heats up the air in your coop. To maintain this heat, you will need to insulate your coop, both the walls and ceiling. This could mean anything from adding solid walls to a wire coop or even using actual housing insulation, but be sure to keep curious chickens away from insulation as consumption of it is dangerous. If insulation is not a technique you wish to try, you can always add a tarp or stack hay bales near walls to keep heat inside your coop. Dark colors are especially helpful when it comes to drawing in heat.
Another factor to consider is how well your coop holds heat. Is your coop drafty? If so, sealing off drafts can go a long way towards maintaining warmth by not allowing warm air to be pushed out. Also, if your coop is elevated, it will get and stay colder than ground level coops. Ultimately, you will be most concerned with keeping your chickens warm through the night and the way to do that is to store as much daytime warmth in your coop as possible. By engineering a coop with lots of thermal mass (absorption of heat for later release) such as an earthen floor and large watering containers (remember, larger bodies of water take longer to freeze!), you will keep the coop temperature stable, which is better for your chickens. Earthen floors trap and hold heat, releasing it gradually throughout the night until the sun rises and the warming process begins again.
Taking precautions to draw in and maintain warmth is far safer than taking risks with electrical and artificial lighting. Do what you feel is best for your chickens and yourself by all means, but do so with caution in mind.