Residential Plumbing & HVAC Experts

Can Poor Indoor Air Quality Be Caused by Problems in Your Duct System?

People spend most of their time at home, so indoor air quality should be very important. The HVAC system uses your home’s ductwork to carry air throughout the space, which means that the condition of ducts plays a major role in air quality. Here are some ways that your ducts could be causing poor indoor air quality in your home.

Ducts With Leaks Can Distribute Pollutants

Everything from the smell of a dead rodent in your home’s crawl space to dust and mold can wind up in your home’s air if ducts are leaky.

Infiltration From Unbalanced Duct Leakage

Leaking supply ducts can affect indoor air quality. The system is supposed to draw air from the house and send it to the HVAC system to be conditioned, then put that same amount of air back into the supply ducts. If less air makes it back to the house because of leaks, this creates negative pressure, and the pressure imbalance will be equalized by air that infiltrates from outside. That air may infiltrate from your garage, attic or crawl space and will likely be unhealthy.


When the gases in a combustion appliance are unable to go up a flue, they go into your home. Some combustion appliances produce carbon monoxide, which can be deadly. Gases may be unable to go up the flue due to negative pressure. Ductwork that’s leaking on the return side in the combustion appliance zone can cause this issue.

Poor Humidity Control

If you have excessive humidity, you’ll most likely have mold since all the other things it needs to thrive — food, air and suitable temperatures — are already available. How does this happen? Poor ductwork reduces moisture control, and many air conditioners are oversized, resulting in short cycles. When leaking ducts draw in even more moisture from a basement or crawl space, the already compromised moisture control can encourage mold growth.

If you’re looking for ways improve poor indoor air quality, contact the pros at Sherlock Plumbing, Heating & Air. We solve HVAC problems in San Diego and surrounding areas.