Smartvent’s patented vapor pressure technology (comparing in-door and out-door water vapor pressures) may be the most effective way to cut crawl space humidity, claims the company. Measured at 295 CFM, this unit exhausts air at a rate a remediation company would employ for a few days to dry out a water-damage situation, states the manufacturer. A single exhauster will usually handle crawl spaces up to 2,400 square feet.