I don't use heat, most types of heaters are a fire hazard. Add to that the fact that if there is a power outtage, the birds wouldn't be as prepared for the cold temps. Some roosters lose the tips on their comb, other than that they do ok. If you decide to insulate, don't use the styrofoam insulation unless you have it completely covered. Chickens love to eat the stuff, and that doesn't mean they'll lay their eggs in cartons. We insulated ours and have a row of windows on the south side. It isn't warm, but probably warmer than outside and all openings being on the south side keeps the wind out.