I live in a cold climate. I have a 2 stall garage and the north facing insulated doors seal very well to hold in the heat. In fact the whole garage is insulated and I even heat it. Holding the building a 45F it takes 2 years between refills with a 200 gallon LP tank. And this is with temperatures than hit -40F over night with highs still well below 0F for several days or weeks at a time. And even unheated, that garage will never drop below freezing over an entire winter.

If you a drafty doors, you are doing something wrong. Fix them.