First year pullets will lay up a storm, their first winter. Been doing chickens for 50 years, up here in Michigan. The hardy breeds like Rocks could care less about the cold. For sure, it is about light, as a chicken is photo reactive. Wyandottes, Buckeyes and others love the cold. They were bred for it.
The modern sex-link layer will lay, lay and lay some more. Trouble is, they don't breed true, much like a CX meat bird, thus, not sustainable.
Folks in Alaska keep chickens without heat. Shoot, there's an entire breed of chickens called Icelandic. Yup, you guessed. They are from Iceland. It's all about the breed if you live up north.