I don't want to get into the whole heat/no heat debate, but for me there is no choice but no heat. I live in northern Michigan, in the valley, and -20 is just another ho hum night in Jan/Feb. How could anyone possibly provide meaningful heat? And, who could pay for it?
Thus, if no heat, no need for insulation either. It just provides the mice a nice home. Yuk.
I use a heated dog bowl and set a one gallon water pail in it. Works great. Use a couple of them. They eat more to keep warm, that's a fact. I've never had frostbite, laying maintains at 75% of the hens per day. It all begins with keeping only cold hardy breeds and there are many, many to choose from.
Finally, think about this. These breeds, a dozen breeds, are American/Canadian breeds. Created in the bitter cold of New England, New Hampshire, Ohio, Quebec, etc. Too many breeds to list. For two centuries these breeds were developed and kept without any thought, ever, to heat. How did all those chickens ever survive that we might enjoy their progeny?
There are 30 chickens, 20 of which were only 3 months old inside that barn the morning this photo was taken this winter. The temp was probably -15.
Hopefully, your confidence is rising?