There has been several posts on keeping chickens warm during the cold of winter. I think many have come to realize that they need to keep the chickens dry, and chickens will keep themselves warm.
Along this thought, go look at your coop, and where the poop is falling, if the poop is landing in near the wall or even piling up against the wall, you need to reconsider your roosts. Those birds are too close to the wall at night. This manure will really hold onto the moisture piled against (in my case) a wooden wall. If the poop is falling out more towards the center of the coop or at least a foot away from the wall onto dry bedding. The bedding holds the poop rather aloft, and it dries out rather quickly. That is what you want.
Your birds need space between them and the wall, between them and the ceiling. That plus good ventilation will really keep them dry, and that will keep them warm. You can see where they are roosting most of the night, by where the poop is landing.