We built our coop without an egg door. We have a pop door (12x12) and a people door (24x16). Everything is double-walled and insulated. My hubby thought that a single-layer egg door by the nest would be too cold. I didn't think of it while we were building the coop, but won't opening a 24x16 door every day in the winter make the coop cold, too?!? Was this a foolish mistake? We could add an egg door, but it will kind of be a pain to do it now. We live in MN. I just want to be sure that our hens aren't going to freeze in the winter if I open the big door every day to collect eggs.
If your coop is draft-free (but still has some ventilation) your birds will be fine in the winter - they generate a lot of heat and many folks - even in northern climates like yours - don't have insulated coops. I live in Kansas - not as cold as you obviously, but my hen's coop is tin - no insulation. On cold days before I get home from work the eggs in the nests will freeze and crack...but the chickens are just fine.
Egg doors are nice when a hen is on the nest when you collect eggs. It is much easy to reach under from behind the birds to collect eggs rather than the big fuss from the front (they peck unless you shooo them off the nest). I just collect from within the coop but when a hen is brooding then I go around back for a reach under. Opening and closing doors is perfectly fine and provides fresh air. Our coop always has a few high coop vents open as well as the pop door for fresh air. The coop will stay fine with a few windows for solar heating and you can add a small brooder lamp in the corner if you wish for the extreme cold. A heated water dispenser is very nice to have so the birds always have water available.
