Think back to last winter in Iowa. Did you see any wild birds around? How were they staying warm?
Chickens don’t need to be kept warm in winter. With their down coats they can do a pretty good job of that themselves with just a bit of help. They trap tiny pockets of air in their down and feathers. These air pockets are what makes feathers such good insulators. As long as a breeze strong enough to ruffle those feathers and let the air pockets out doesn’t hit them they stay plenty warm. So your chickens need to be out of direct breezes strong enough to ruffle the feathers.
Ventilation is pretty important too. Wild birds are not cooped up. Even if they are sheltering out of a strong wind they still have good ventilation around them. Some people think you need to close the chickens up pretty tightly in winter but not so at all. Chickens and other birds have fairly delicate respiratory systems. If you close them up tightly the air can get pretty foul from their poop. The poop creates ammonia as it breaks down. Ammonia is lighter than air and can really mess up their respiratory system. If the poop is frozen it will not break down and form ammonia but if it is not frozen solid, they need openings above their heads so the lighter-than-air ammonia can escape.
The biggest danger from an enclosed coop is frostbite. The moisture from their breathing and their poop needs to escape or it can cause frostbite in temperatures below freezing. This is really where you need good ventilation. Their poop and their breath are warm, at least at first. Warm air rises and holds more moisture than cold air. Again openings above their heads really helps get this extra moisture out. It doesn’t take much of an opening to get the ammonia out, the moisture takes more. But if the openings are over their heads and a breeze develops between those openings, that breeze does not ruffle their feathers because it is over their heads.
My winterizing the coop consists of closing a window below roost level and rely on the openings along the roof line for ventilation.
They do need clean water. That might be your biggest challenge. If you have electricity out there you can get heated pet bowls, make a cookie tin heater, or maybe something else. I use black rubber bowls that I got at
Tractor Supply. When the water freezes in them you just turn them over and bang them to get the ice out. The rubber won’t break. If the sun is shining that black rubber acts as a solar heater. One of those in the sun will stay thawed at a surprisingly low temperature but they are certainly going to be frozen solid in the morning. The sun doesn’t always shine either. It’s a bit of work but it works for me.
I never leave mine locked in the coop. I give them the option to go out or stay in as they wish. As long as a strong cold wind is not blowing or the ground is not covered in snow they practically always choose to go out, even in sub-zero Fahrenheit weather. Usually they don’t like snow when they first see it but if snow stays on the ground for a few days they get used to it and will go out in it.
You’ll see different people say they feed their chickens various things in winter to help them stay warm. That does absolutely no harm as long as you don’t get carried away with that stuff. Many people are convinced they need to feed something special for cold weather, corn is often mentioned, but many of us don’t feed extra like corn and our chickens still stay warm. How much it actually helps the chickens is debatable but if it makes you feel better it has value.
Even in winter they need a balanced diet so don’t overdo the treats. Their regular feed provides a balanced diet and should be the main part of what they eat. They will not forage nearly as much when the ground is frozen or covered with snow so you need to see that they have plenty of chicken feed to eat. That’s basically it.
Good luck! They really do handle cold pretty well on their own with just a bit of help.
