It's hard to say. My recommendations are for large fowl, cold hardy breeds. I would not own a chicken that's not cold hardy because of my climate. Adding the fact that they are old and frail, they are definitely more susceptible to having problems through the winter. No guarantees there.
Their average body temperature is 106 F. I have a tree hugger neighbor. Sorry take no offense. She is all worried that I haven't insulated my coop. Try this: breathe on your hands get them nice a moist and then go outside without gloves. How long will you last. Chicken have a high metabolism. They breathe off a lot of moisture. You should worry about that fact. I live in Maine. Had 2 chickens up in the coop when it was bitterly cold a couple of weeks ago. I didn't have a tarp around the run either and they were fine. The first thing I check in the morning is their combs. No frostbite, actually feel quite warm. They do tuck their heads under a wing and snuggle over that feet at night. Now I have the run cover tightly with clear tarp. They will be fine. I'm not much for the wine part but the rest is good advice.
They turned out alright. When I went into the coop they were active. It was actually warmer in the barn than outside for some reason. I thought a barn just offered shelter from the wind, but apparently it helps with the temperature as well. Not much warmer, but it definitely took the edge off. The days following Thanksgiving have been warmer as well, so the cold snap should be over. One heater is working above the roost now and is heating them at night on their roost. We are working on fixing the other heater above the roost. Hopefully they will be okay in the winter months to come!
I would not close off that ventilation if there isn't a draft blowing directly on them. Chickens with big, floppy combs are more prone to frostbite, and the more moisture in your coop, the more likely they are to get frostbit. Chickens can get frostbite in a too-humid coop when the temperatures are relatively warm. Don't beat yourself up over it, either. Lesson learned - try to have chickens with smaller combs. Your chickens will be fine, by the way. Don't mess with the combs. They will be "winter-dubbed", but should heal without any trouble.
