What if the power gets knocked out for a few days in 0° weather. Your birds are going to suffer because they won't be accustomed to those temps.My coop is fully insulated ( R-5 and Reflectix) with no drafts and appropriate vents. Still, gets down to 30 F. I finally found safe solution with a 700 watt oil filled heater and a 12 gauge 50 ft exterior extension cord. Keep temp at 62 during the night. Cord runs through PVC pipe. Added PVC to small section from heater to exterior not seen in photos. The heater box is mounted to the post above the wood shavings.
Majority of folks say they are not uncomfortable. However, my bantam roosters seem cold to me. It makes me feel better. It has been as cold as 1 degree F outside and my boys are so happy to be in their digs.
Coop is ugly but no leaks and predator proof.
-11 here last night. My birds are just fine this morning.