You all know that most of these breeds we keep were developed over the last several hundred years in pretty cold climates and they had no means, desire or need to heat housing.
Their ancestors, red jungle fowl, are adaptable to a wide range of climates and their original range went all the way into the Himalayan foothills.
Lets look at a few breeds people keep.
Plymouth Rocks - it got pretty cold in Massachusetts in the early 1800s.
New Hampshires - it was very cold in New Hampshire in 1915.
Delawares - it was pretty cold in Delaware in 1945.
Jersey Giants - it got really cold in New Jersey in 1880.
Buckeyes - very cold in Ohio in 1904.
Chanteclers - it is cold in Canada, but it was in 1918 too.
Barnevelders - it got pretty cold in Holland around 1900.
Dominiques - known as the Pilgrim chicken, it traversed the United States with the pioneers, I doubt they had very cozy housing.
Ameraucanas - developed from chickens originating in Chile - very chilly in Chile.
Swedish Flower Hens - yeah it was cold there hundreds of years ago.
I could go on.
I've had about 30 or so breeds of chickens and it gets into the minus teens here. My newest coops have huge windows on both East and West walls that take up nearly a third of the walls. I've never lost a bird to cold but I have lost birds to heat.
A friend has a very nice coop and covered run. For the last 3 years, her birds have opted to roost in the wide open run rather than the coop - all winter long.
Healthy birds don't get stressed or sick from cold if allowed to become acclimatized. Continually going from warm to cold is stressful.