As warm air rises through a home it escapes through attic vents. New air must enter to replace the air that has escaped. This creates a suction at ground level through the open crawlspace vents. (that's why some houses get the "musty" or "earthy" smell in the warm months). Up to 50% of the air you breathe comes from the crawlspace. If your crawlspace is damp and musty, so is the air inside your home. If there is mold in your crawlspace, there are also mold spores circulating through your home. Solution? Have your crawlspace encapsulated! It's cleaner and more energy efficient.