Like you, I live in snow country, and had the misconception that my girls needed a heated coop...if I'm freezing my buns off they must be, too...not! It's not heating the coop we should be worried about this winter...it's the humidity the flock produces from their own body heat. Humidity/dampness is what'll get them. And they do need ventilation...no direct drafts especially toward the roost area, but they do need fresh air to help expel the humidity.That would be devastating!
As they say, A picture is worth a thousand words. That should get everyone's attention. I certainly did get mine. And being new to all of this, and reading everything that I could, I'm planning on letting my chickens supply the heat. I do plan on heating the water though. I'm going to make the cookie tin heater, and ordered a thermo cube from walmart yesterday.