This will be our hens' first winter in cold, snowy Minnesota. We selected winter-hardy breeds (3 Buff Orpingtons, 2 Leghorns, 4 Rhode Island Reds, 1 Speckled Sussex, 2 Americaunas, and 1 Barred Rock). They've got a well-constructed coop--with adequate ventilation and little or no drafts. But the recent string of colder weather is making me nervous about getting the girls through the winter comfortably. Here in central MN, we'll likely see temperatures in the negative teens. Any tips for keeping a coop warmer without creating a fire hazard? How do all you other cold-weather survivors help your flock?