While many IAQ (Indoor Air Quality) problems are caused by building issues, the HVAC system can also have a direct or indirect impact on of poor air quality.
Some indoor pollutants including Volatile Organic Compounds (VOCs), Radon, biological growth (i.e. mold), and dust can be caused by the home or building. Sources of these pollutants include poor construction practices, foundation and/or slab moisture, poor insulation, even lack of maintenance.
With some good building science training, as an HVAC contractor you can help identify the causes of these problems. But unless you are ready to take on remodeling and other building-side corrective actions, it’s usually a good idea to refer that work to another professional.
When Is the HVAC System to Blame?
Many IAQ issues are a direct result of an improperly designed, installed, or maintained HVAC system. Certainly, you can recommend some of the traditional remedies like better filtration, dehumidification, even UV lights and other products. However, unless the product truly targets the source of the issue, it will be just a band-aid, and the actual causes will continue to exist.
So when is the HVAC system a direct or indirect culprit? Let’s start with some of the more obvious direct issues. These include return duct leakage bringing in dirt, dust, and other pollutants from unconditioned areas like attics and crawl spaces.
Moisture buildup in and around the air handling equipment, especially in coil drain pans, can cause IAQ issues. Indoor coil blow-off from high air velocities also introduces moisture into the duct coil-condenser matches. Improper system matches can reduce dehumidification as well.
Improper system sizing can directly contribute to IAQ issues, especially in higher humidity areas. An oversized cooling system will short cycle, dropping the indoor temperature but never running enough to remove the moisture. The symptoms are typically a cave-like, cold, clammy interior space, where mold and mildew easily grow – check shoes in a closet for mildew!
Some of the indirect HVAC causes for IAQ issues include poorly designed or imbalanced air distribution systems. The results include drawing dust, dirt, insulation, and moisture from unconditioned spaces through can lights and other building envelope openings.
Poor air distribution systems with high static pressures and low airflow can condition some areas while others are hot or cold. As a result, parts of a home or building can be comfortable and healthy while others remain uncomfortable and unhealthy due to stagnant air, high CO2 levels, and other related issues.
Finally, a major issue caused by pressure imbalances is carbon monoxide. Negative pressures near combustion appliances including furnaces, water heaters, boilers, even stoves, can cause back drafting or spillage.
This leads to re-burning of combustion gases producing carbon monoxide levels that can range from unhealthy to dangerous.
The bottom line is when you’re in a home or commercial building with IAQ issues, it’s important to know how to test the performance of the HVAC system in addition to looking for visual clues for sources of indoor pollution.
When you take the time to thoroughly test, you also help protect yourself from liability. Plus you can make more accurate recommendations to fix the building or the HVAC system – or both.