I live in Alaska and we get much colder for much longer here than what you said, I know people who do others who dont heat here no matter 58 below 0 or not. I do heat mine, I have a flat panel heater on a timer and another on a thermostat for if it gets to 34 above.
I think the biggest thing is to have plenty of ventilation with out drafts. People dont seem to think about that when they make a coop and by winter being all shut tight for how ever long they wonder why there is watter dripping off the walls and the flooring is wet
I love my heater it is ment to be in wet areas is totaly contained and even when on I can touch it and not get burned it goes a great job on my 12x12 winter house. It sits off the wall a bit and lets the hot air rise up both behind and infront of it and my girls fight for my seramas roosts above it even though the roost is only 9 inches off the roof. Nothing like seeing a huge blue Orp squeezed in the tiny spot!