Duct Sealing to Improve Air Quality

Q: I don’t see any holes in my HVAC ducts, but should I still have them sealed to improve energy efficiency and indoor air quality?

A: Duct leakage plays a major role in not only your energy bills and indoor air quality but also the comfort and durability of your home. Even when homes are reportedly sealed, air tightness tests can reveal issues. Professional HVAC companies, home energy raters and building code officials rely on testing to make sure ducts are properly sealed.

When looking for leaks in duct systems, professionals don’t only look for larger holes but also small gaps, pin holes and unsealed joints that can add up to a big problem. Research estimates that many North Carolina homes built prior to 2012 lose up to 25 percent of heated and cooled air through duct leaks. Considering that heating and cooling is often our home’s largest energy expense, sealing ducts may be a sensible energy-saving home improvement. Since 2012, the North Carolina Building Code has required that all forced-air HVAC systems in new homes pass tests proving they are losing no more than 6 percent of heated and cooled air.

Improved indoor air quality is often another benefit of properly sealed ducts. Like a rip current dangerously pulling a person from the ocean shore, tiny holes and gaps in an HVAC system may suck dust and unsavory air into the system and ultimately circulate it in your home.

When looking for duct leaks, start indoors by removing the grille from the air supply and return vents. Is there caulk or foam sealing the gap between the metal boot and the ceiling, floor or wall? Even a gap as thin as a one-sixteenth of an inch can add up to a big area if you consider the same gap around the other 10 to 20 supply vents in your home. Dirty or rusted air supply grilles can also be an indicator that the HVAC system is blowing attic or crawl space air into your home.

Next, go peek at the HVAC ducts and air handler. All ducts should be securely connected to one another, the HVAC unit, and the floor or ceiling. Look below the duct insulation to confirm that the duct joints are covered in a dry paste called mastic. Research has shown that tape alone is often an inadequate joint sealant. An HVAC professional will be able to seal all parts of the HVAC system and test it to ensure it meets the agreed-upon duct tightness.

Contact your electric provider to ask about duct sealing incentives, recommended HVAC professionals and guidance for duct sealing. When selecting an HVAC company, solicit estimates from at least three and be sure they include air tightness testing as part of their package. Contact at least three references from each company to make sure the HVAC professionals were respectful, timely and did quality work. Reducing duct leakage is a good first step for improving a home’s indoor air quality and energy efficiency. The payback is well worth it.