I'm freaking out about the cold too. I have a well ventilated coop. All of the ventilation is up high. I also do the deep litter method with large pine flakes. My coop is not insulated at all but is solid. I have a thermometer against the wall in there and I also put one on the floor last night and I have a little screen inside my house that tells me the temps. The temp at roost hight is 16F, the temp on the floor is 19F. The temp outside according to the weather app is 12F and wind chill is -3F.
Yesterday I put an oil filled radiant heater in there, I made a sort of stand for it and it has a little fence around it so that they cannot get to it to knock it over or roost on it. I haven't turned it on yet but I think I will turn it on for a couple of hours here and there, to give them some relief over the next few days. I am also considering putting their food and water in there if it is quite windy that way I can shut the pop door. Everyone seems to be quite firm on not putting water in the coop though.
We'll see. Also, I do have 36 chickens in there, and they are all 14 weeks old. I do recommend the deep litter method with the large pine flakes. The chickies love it.