Here’s how I responded in your other duplicate thread just in case you didn’t see it.
https://www.backyardchickens.com/t/1022422/how-do-i-keep-my-chickens-warm
You don’t keep them warm. You allow them to keep themselves warm. What do you do to keep the wild birds warm in your winter?
I’ve seen chicken sleep in trees in below zero Fahrenheit weather. One trusted forum member told a story about chickens going feral in northern Michigan and surviving the winter in the open, even foraging for themselves and probably eating now for water. I won’t say they thrived in that Michigan winter but they survived. With a bit of help they can thrive. Those chickens were not roosting on a bare tree limb overlooking a cliff, squawking defiantly in the teeth of a blizzard. Like the wild birds they found protected places out of the wind but with great ventilation.
Chickens keep themselves warm by trapping tiny air pockets in their down and feathers. Their body heat warms these tiny air pockets and that provides insulation for them. If a wind strong enough to ruffle their feathers hits them and releases those air pockets, they can get cold. So provide them a place to sleep where the wind doesn’t hit them directly.
You want gentle air movement though. You need to remove the ammonia and excess moisture from the coop. Ammonia comes from their poop decomposing and can be hard on their respiratory system. Moisture comes from poop and their breathing and can lead to frostbite if the temperature is below freezing.
You need good ventilation but you don’t want to have a strong breeze hitting them. There are many ways to do this but easiest way to me is to have openings high over their head when they are the roosts. Ammonia is lighter than air so it will rise. The air is generally warmer in the coop than outside so even on a perfectly calm day there is air movement up. If the wind is blowing outside, and strong breeze will be over their heads but will create a tiny bit of turbulence to suck the bad air out of the coop.
With decent breeze protection and good ventilation, your only concern in the winter should be keeping the water thawed.