According to mold industry standards, I am required to have a crawlspace fan installed when there is mold in a crawlspace, unless for some strange reason the client wants the crawlspace clearance tested. Which cleaning a crawlspace to pass an air test is very labor intensive and expensive. All vents have to be closed so the fan creates a slight negative pressure and pulls conditioned air from the level up above.
I was talking to a waterproofing company and they claimed crawlspace fans cause what they called a reverse stack effect. A crawlspace fan only completely changes out the air in a crawlspace about every 15 minutes. I do not see how this could cause smells coming from the attic like they claim, unless possibly the attic is not properly vented.
Any thoughts would be greatly appreciated.