We get really cold here, it used to go to -40, but the last few years it has been warmer. We close the coop up pretty tightly, but it still leaks enough that we have some ventilation. We have a lot of vents for the summer that are enclosed with hardware cloth. For these, we bunch up newspaper and cram it into all the vents, including the one up top that is a spinning vent. The newspaper allows for moisture to escape, but cuts out the harsh winds. The ceiling gets panels of 2" styrofoam added. Bags of leaves are stacked up against the outside walls. When the snow comes, it is also shoveled up on top. The waterers are changed to heated dog bowls. Since we have to collect eggs twice a day, hot water is brought down to them twice a day. In order to keep them laying, a light would go on at 4:00 a.m. and off again about 9 a.m. When the kids were raising show bantams, we had a lot in cages, so there were a lot of small waterers that were frozen solid. The kids would bring a couple of 5 gallon buckets down and put all the frozen water containers into the buckets, then replace them with fresh, hot water. Then, they had to carry all those up and dump them in the laundry tub where they would thaw out and drain. They were all cleaned out and put into the 5 gallon buckets for the next trip down to the coop. It was never fun during a blizzard making the 200' trip down to the coop. I am so glad that this year there won't be any in cages. I also insisted on no Polish - I could never stand those frozen feathers clinking like icicles!
We never got any frozen combs, but we did coat them with Vaseline a few times when it was super cold. We also ran a small heater when it got colder than -20. The heat of the chickens themselves usually kept the coop 10 to 20 degrees warmer than outside. We also have two sets of doors. First we enter the front section of the coop, then shut the door tightly, then enter where the chickens are. That way, there is no huge cold wind.