I live in upstate NY about 3 miles from the Canadian border. This is my first year with chickens and I'm not sure the best way to winter proof their pen. I am housing my chickens in a section of a old cattle barn with a door leading to an outside pen. It's definitely not air tight and has a lot of draft which is great for the summer but won't be good this winter. I know they need ventilation but this goes beyond ventilation. I can't use a heating lamp due to extreme risk of catching my barn on fire. Do you have any suggestions on how I can keep them warm over the winter?