Air Ducts People. By far, the most popular of all central HVAC systems is the ducted forced-air system. While the mechanical elements of these systems seem to be constantly evolving in efficiency and dependability, the ductwork that distributes heated or cooled air throughout the house has not changed much. Though ducts are used to cool a home, they usually run through unconditioned areas like attics or crawl spaces. Sometimes leaks can occur in the duct system.
Conditioned air lost through duct leaks is a net loss for the homeowner on two accounts.
The homeowner loses conditioned air and unconditioned outdoor air is drawn into the home. Even the most carefully weatherized home is not airtight. Outdoor air can enter the home through cracks and small holes in window and door frames, through exhaust fan ducts and even through permeable surfaces like sheet rock interior walls. Outdoor air usually stays outside because there is no driving force pulling it in. A duct leak, on the other hand, represents a loss of indoor air and a gain of outdoor air driven by the fan in the HVAC system.