Duct Drama: When Your HVAC Turns Your Home Into a Vacuum
"Why is it so humid in here?” The air conditioner is running, but I can feel the humidity creeping in. I won’t stop talking about it. My wife senses my impending obsession and tries to change the subject. It doesn’t work.
“Should we get humidity sensors? Honestly, it might be worth looking into dehumidification. I don’t think our A/C can keep up.” Soon after, I found myself sweating and contorted in our very cramped attic space. It’s dark, it’s gross, and it’s mildly creepy. To my dismay, almost none of our ductwork has been properly sealed. We are hemorrhaging money in the form of conditioned air. I'm indignantly rambling - something about poor workmanship and “how it should be,” you know the one.
Today, let's talk about leaky ducts and their costly, sometimes gross, implications.
Why It's Gross
We’re all impressionable—I get it. But if someone asked you to start breathing the stale, dust-laden air that makes up your attic and crawlspace for recreation, I’d bet you’d say ‘no, thanks.’ Yet, if you’re like many North Carolinians, your ducts and air handler/furnace are probably in the attic or crawlspace. Guess what that means? You’re likely pumping that air into your home because your HVAC system isn't properly sealed.
Let's tie this back to a recent study by Duke University, which examined bioaerosols in crawlspaces. These bioaerosols include dust mites, cockroach excrement, and fungal spores—delightful! Their findings reveal that houses with crawlspaces in forested areas of the Piedmont region often have higher bioaerosol levels; however, “Over half of the homes sampled experience some type of bioaerosol problem” (Hale & Miranda, 2005). This underscores a significant issue: return duct leaks can pull airborne pollutants, spores, and moisture into your home’s living spaces, worsening indoor air quality.
During their study, Duke University also discovered alarming conditions in many homes: “Thirty-three percent of the houses showed condensation on duct or pipe surfaces, 16% had waterlogged ducts, and 31% had plumbing leaks. The majority of homes (62%) had visible mold in the crawlspace” (Hale & Miranda, 2005). The last bit isn’t surprising given the dark, humid environment of crawlspaces, which fosters mold growth exacerbated by condensation and plumbing leaks. If you store items in your crawlspace, you might want to reconsider, as bioaerosols can be pulled into your home alongside gas, VOCs, or other strong fumes.
Notice that bioaerosol levels become higher inside as the HVAC gets turned on and raised further when invasive sampling occurs in the crawlspace. Remember, these are averages. Houses in the Piedmont of North Carolina that are older likely see much higher levels, particularly with poorly sealed HVAC.
Why It's Costly
According to Energy Star (2024), "Leaky ducts can reduce heating and cooling system efficiency by as much as 20 percent." The Lawrence Berkeley National Laboratory (LBNL) indicates that duct leakage can account for 10-30% of heating and cooling energy use in a typical home, potentially saving households around $200 per year if sealed. I’m amazed there are agencies dorky enough to be this interested in duct leakage. But—hey—the numbers are in! Addressing duct leakage is crucial for both energy efficiency and cost savings.
But apart from blowing conditioned air where it does not belong, those holes in your ducts create an imbalanced system where more air is sucked in than blown out into your home. When your HVAC system pulls in air faster than it pushes it out, your home becomes depressurized, like a balloon shrinking inward. This vacuum effect draws air through walls, attics, crawlspaces, windows, and doors, making it harder for your system to condition and dehumidify indoor air effectively. While lowering the thermostat may briefly feel cooler, you ultimately spend more conditioning outdoor air while feeling less comfortable doing it.
Why less comfortable? Because your HVAC also acts as a dehumidifier; which is crucial in North Carolina’s humid climate. When it pulls in excessively humid air it can’t effectively remove moisture. As a result, your home feels less comfortable even at lower temperatures. A well-designed HVAC system can maintain comfort at higher temperatures by effectively managing humidity levels - saving you money.
But how pervasive are leaky ducts? Our friends at Duke found during their study that “65% had major duct leakage, 18% had excessive leakage, 9% had moderate leakage, 4% had limited leakage, and zero had minimal leakage.” (Hale & Miranda, 2005). Not good - really not good. The kind of ‘not good’ that leaves you in your home feeling hot, humid, and dusted in cockroach particles.
Why should you care?
When I was a contractor, I saw firsthand the impact of poor duct sealing on homes. Beyond visible issues like mold and moisture, leaky ducts compromise comfort, increase energy bills, and expose homeowners to airborne pollutants. This experience has been paramount in shaping my perspective as a home inspector. Potential homebuyers should understand what they’re inheriting when purchasing a new property, and homeowners should consider having their ducts inspected and sealed by a professional to enhance their HVAC system's performance. This investment not only reduces utility bills - it also improves overall comfort and indoor air quality. Regular maintenance and proper sealing of ducts can prevent energy loss and ensure that the heating and cooling systems operate at peak efficiency. Book a service with us today and avoid duct drama!
Sources
Hale, B. W., & Miranda, M. L. (2005). Assessing allergens and asthma triggers in the home environment: A study of the southeastern United States (Final Report). U.S. Department of Housing and Urban Development, Office of Healthy Homes and Lead Hazard Control. Duke University. HUD Grant No. NCLHH0096-01.
Energy Star. (2024). Duct sealing flyer. Retrieved July 8, 2024, from Energy Star
Lawrence Berkeley National Laboratory (LBNL). Retrieved from LBNL
