Crawlspace ventilation fans or power vents causes all the humidity evaporating off the damp dirt, damp foundation walls, and hot humid air from the other crawlspace vents to be drawn to one central spot; the power vent itself. This always makes the area around the power vent more humid than the rest often creating mold and wood rot in the area. Ventilation is 100% climate specific. Ventilation works better in Arizona than Tennessee. Tennessee is too tropical and humid for ventilation to be effective. Air sealing the entire crawlspace off from all humidity sources is the only real solution.