Just to let you know not to worry so much about the cold and your chickens. If bedding is nice and deep and I mean deep like 8 inches or more you should be fine. I have not used heat in my coop all winter. Roof is not sealed at edges either nor are the window cracks( windows are not glass just board). My coop is 8x8x8 with 22 chickens in it. They free range everyday no matter what the weather. Last pics on their blog shows them going out in snow. I have yet to see any frostbite at all. There perch is a branch about 2 1/2 inched diameter. I have chickens sleeping on the floor as well as on the perch. Bedding used is wood chips covered in straw. Chickens are very hardy try not to worry about a cold snap as long as it is above 0 your coop will be warmer than outside by at least 10 to 20 degrees more most likly more than that even.