My Colorado climate can reach -40º in winter. Water pipes freeze in crawl space, but I'm not really sold on heat tape and space heaters are scary, including infrared gas, etc. Current gas fireplace with forced air fan heats entire house. Could I use a ducting device or a thruwall fan to move warm air DOWN to the crawl space during the winter? I don't want crawl space air flowing back into the house, as there are some mold/mildew problems. Thanks for your help!