Up to 30 percent of a home’s heating and cooling energy can be lost through leaks in the ducts of a forced-air system, especially in those located in unconditioned attics, crawlspaces, and basements.
Leaks can result from improper installation and occur within only a few months of occupancy, leading to homeowner complaints about high energy costs and poor indoor comfort well within a builder’s warranty service window.
The problem is two-fold: First, duct runs located in unconditioned spaces create pressure differences between the air temperature within and outside the duct that magnify and eventually exacerbate leaks and thermal loss through the ducts.
Duct connections are the other problem area. Whether old-school sheet metal or new-age flexible runs, the joints at the furnace plenum and between duct sections are ripe for leaks upon installation and over time.
The resulting air and thermal loss reduces the efficiency of the heating and/or cooling equipment (read: a four-ton unit may be reduced to a three-ton capacity), hindering its ability to maintain desired indoor temperatures and occupant comfort as designed and calculated on the spec sheet.
Commission a duct blast test just prior to occupancy to identify and seal leaks, and consider insulating areas where ducts run to reduce temperature and pressure differences.