Relax. I have already had sub zero temperatures this year and it was down to 1°F last night. I regularly see -30°F at some point during the winter. My chickens do fine without any supplemental heat. Good ventilation, no condensation and a dry coop will be fine. At some point, have an electric line run to the coop so that you can eliminate the extension cord.Crazy...yes! Absolutely...! I am a pacing, frantic piece of a human right now!