Builder tip: Earn the duct seal of approval

It’s amazing how much energy a home can waste when the ductwork isn’t properly sealed. In fact, leaky ducts can result in heat loss of up to 20 percent, and that’s not good for anybody’s monthly bills. Build your homes to avoid these issues by properly sealing ducts from the beginning. Thorough, complete duct sealing will increase the heating and cooling system’s efficiency, and help homeowners lower energy costs and improve comfort and indoor air quality. Plus, it’s one of the features that can help you earn an EPSTM to promote the high quality and efficient performance of your homes.

While it’s important to pay careful attention to all ductwork, the biggest trouble spots involve ductwork in unconditioned areas such as attics and crawl spaces. These areas suffer the greatest losses when it comes to heating and cooling system performance. To overcome this leaky duct dilemma, it’s critical that mastic paste is properly applied when the duct system is installed. Mastic can be applied with a disposable brush, by hand with a glove, or with a putty knife. Just be sure HVAC contractors use mastic paste applied at least a nickel thick, not tape of any kind. Extensive testing has shown that tapes— even expensive UL listed mastic tapes—don’t hold up over time as well as mastic paste.

To minimize air leakage, use mastic paste to seal all connections, seams and joints. This includes the air handler, which can be a main source of leakage if the seams aren’t properly sealed around the sheet metal housing. Because mastic can be messy, many HVAC contractors find it’s easiest to put it on the inside of fittings before they’re assembled. This is often done ahead of time under controlled conditions.

Being thorough with duct sealing brings a host of benefits beyond improving efficiency and lowering energy costs. It can solve common comfort problems, such as rooms that are too hot in the summer or too cold in the winter; it improves indoor air quality by reducing the risk of fumes and pollutants entering the duct system, and it can help with proper air balancing.

Energy Trust support and resources

For more information on duct sealing, including an online training video, plus other valuable builder resources from Energy Trust, visit our training webpage or call 1.877.283.0698.