Conditioned crawl spaces bring the HVAC equipment, air handler, and ducts into conditioned space. Any duct leakage is lost into the building envelope. Conditioned crawl spaces eliminate moisture intrusion, control relative humidity, and improve indoor air quality. By creating a mini basement, the foundation walls are insulated instead of the crawl ceiling. Conditioned crawl spaces require supply air only (no return), 1 cfm per 50 square feet of floor space.