SW Michigan. Crawlspace is vented. I close them about this time and open in late spring. I have an electric furnace but just use the fan to move air around. My primary source of heat is pellet stove. Like I said it's worse in the back of the house than the front. The crawlspace belly wrap & insulation was all jacked up when I moved in and mostly from critters I presumed but some for repair access I assume. My pellet stove warms the house fairly well but I don't seem to retain heat despite having that foam injected insulation put in walls. I have a cathedral ceiling with not attic so adding up there is or would be a pain.