Earlier this month we experienced three consecutive days of -20 degree Fahrenheit daytime temperatures. Although I believe chickens to be outdoor animals, that was just too cold for my hens to keep each other warm. So they came indoors to the basement bathroom for a few days. It was more than a circus!
A five pound hen generates about 10 watts of energy, so a flock of birds can usually warm each other, especially if they're in a barn with other farm animals. But our little flock of urban birds needed a bit of extra help.
This week we're heading into another polar plunge, but this time we're ready for it. We've installed two ceramic infrared heat emitters in the ceiling of the hen house. (We have no hope of keeping the entire coop warm because it's too large---6 x 8 feet and 7 feet high. But the raised hen house is only 3 x 6 feet and about 3 feet high.) These heat emitters do not emit any light. We've tried using red heat lamps, but it keeps our girls up and chattering all night long and sometimes drives them right out of the hen house. The ceramic heat emitters will keep the air temperature just marginally warmer than the outdoor temps. This is good enough for us, because we don't think it's entirely helpful to raise the temperature too much.
Ceramic heat emitters are designed for reptile pets. Many thanks to Ellen and David for pointing us in this direction!