Can a Poor Duct System Affect the Indoor Air Quality in Your Home?

The air you breathe inside the home impacts your health, and the ductwork has a significant effect on air quality. Good ductwork design and properly maintained ducts go a long way to ensure the conditioned air flowing into the home is clean and safe. However, problems in ductwork can lead to the following air quality issues.


Return ducts that suck in air from damp areas like basements pull in moisture and add to humidity within ductwork. This invites mold growth both within the ducts and within the HVAC system itself, which means your indoor air may be filled with mold spores.

Infiltration of Odors and Polluting Particulates

Leaky or disconnected ducts that are in filthy areas, such as a crawl space, can pull in unwanted odors and particulates. Anything that can enter ductwork is capable of compromising your indoor air quality.

Infiltration of Unfiltered Air

The duct system is intended to function with air flowing from the return ducts to the supply side in a way that maintains equal pressure inside the home. When this occurs, the air you breathe indoors is filtered through the HVAC system’s air filter. However, when there are leaks in the ducts, this often causes negative pressure in the home. Air will be drawn in from other sources to balance the pressure. These sources include cracks in the wall or windows, air from attics, crawl spaces or garages. This unfiltered air mixes with your filtered, climate-controlled air and reduces air quality and home comfort.


Backdrafting is a serious potential consequence from leaky ducts located near combustion appliances. Instead of poisonous gases such as carbon monoxide traveling up the flue to be safely released outside the home, pressure imbalances cause the flow to reverse. This means these dangerous gasses flow back into your living space.

For more information about indoor air quality and ductwork, please contact the home comfort experts at Beyer Boys.

Our goal is to help educate our customers in the greater San Antonio, Texas area about energy and home comfort issues (specific to HVAC systems).

Credit/Copyright Attribution: “photoBeard/Shutterstock”

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