A Fresh Air System cannot be as effective if the high levels of humidity generated by today's shower and tub systems is allowed to dissipate throughout the entire house. It should be removed at the source by running a bathroom exhaust fan for 20-30 minutes after each shower. Your bathrooms should be properly measured and fans for each room must be chosen with proper CFM (Cubic Feet of air per Minute). Then the house's general ventilating system can control the moisture.