My personal notion on Winter temperatures is that chickens are fairly comfortable even when their environment is close to 32°F. There are a few factors to be considered here, however.
First, as has been noted, they require drinkable water. Also, eggs will freeze and break at some point.
Even tho' they have feather insulation, chickens originated in South and Southeast Asia. Some of the breeds have been selected for colder climes but they did not develop as a species in those parts of the world.
I had pigeons for a good number of years. They live wild in the coldest cities of North America. My birds' feed consumption would spike during the Winter months. I haven't noticed as much difference with chickens but pigeons can eat 3 times more food. How much do you want to spend on your birds at the feed store?
Heating costs money, so going beyond insulation and draft-free may not make much economic sense. It may be cheaper to just pump the extra calories into their feed bowl but I think we can only take that so far.
If we go with
production guidelines, housing should be maintained as close to 70° as possible throughout the laying cycle. For the backyard flock,
the Coop Ex experts say, temperatures above 55° are "desirable" to maintain egg production. 55° is a long way from freezing temperatures and below.
Steve