Seal Ductwork

Leaky ducts can lead to a host of problems such as indoor air that is too dry or too humid, condensation, and buildup of dust and dirt that is then redistributed through the equipment and throughout the home.

Leaky ducts can also create pressure imbalances in the home because equal amounts of supply and return air aren’t being delivered. With significant supply duct leaks to unconditioned spaces, the home is depressurized, which drives infiltration of outdoor air. The return ducts are pulling more air back to the equipment than is being supplied. The opposite happens when there is substantial leakage on the return duct side and portions of the home become pressurized. Under these conditions, conditioned indoor air is forced through small cracks or crevices that may exist in even the tightest building envelope. In either case, when air is traveling through building cavities, it is likely to carry moisture. When this air finds a cold surface, chronic condensation can occur.

• Seal ductwork with mastic or approved foil tapes (UL 181-A compliant). Seal ducts at the following locations:
  • All transverse and longitudinal connections and seams,
  • Ductwork connections at equipment,
  • Connections between ductwork and register boots,
  • Connection between register boot and subfloor, ceiling, or wall,
  • All holes in heating and cooling equipment, and
  • Gasketed access panel and filter slot.
• Strive to achieve total duct leakage less than or equal to 4 cfm per 100 sf of conditioned floor area when tested at a pressure differential of 25 Pa.