We've had highs in the single digits the last few days and lows well below zero at night. I have five hens in a converted garden shed that is mostly insulated. When the temps get this low I use a heat lamp and a small flat panel heater (I'm very disappointed in it) to keep them warm at night. I'd like to find something other than the heat lamp, because even though the light is red it still seems to throw off their sleep cycle a little and make them a bit cranky. I looked at ceramic heat emitters, but I am not sure what size is appropriate for my space? The coop is 6' tall in the center, and the 10'wide x 6'long. I think if I had more hens they would probably stay warmer but that's a chicken math problem for spring.