How Can You Prevent and Combat Mold in HVAC Equipment?

While the potential for mold exists almost anywhere, mold in HVAC equipment is particularly troublesome. Specific conditions that support mold contamination in these components are not uncommon. Active mold growth continuously releases microscopic reproductive spores that may trigger allergic responses and even chronic illness in sensitive individuals. Here’s how and where mold may gain a foothold in home HVAC systems:

Central Air Conditioner

The AC evaporator coil produces gallons of condensation daily, collected in the condensate drip pan beneath the evaporator coil, then diverted into a household drain. Dormant spores circulating in system airflow spawn active mold growth in the wet drip pan. Mold often clogs the system drain line, triggering overflows that cause indoor water damage.

High-Efficiency Furnace

Furnaces with efficiency ratings above 90% typically generate extra heat by condensing water from furnace exhaust gases. The presence of warm water, compounded by other factors, support mold growth that clogs the drain system. If drainage is obstructed, a safety sensor may shut down the furnace, requiring professional service to restart the unit.  


Airflow from the AC or furnace circulating through household ducts often contains dormant mold spores. Condensation creates a favorable environment for hidden mold growth in the dark, dusty interior of ductwork. Spores released from mold inside ducts circulate throughout the entire house and may trigger allergic reactions in those who have allergies.  

To reduce the potential for mold in HVAC:

  • Schedule annual preventative maintenance with a qualified HVAC contractor for both the central AC and the furnace. The service includes cleaning the drip pan as well as checking for proper drainage function. If mold in HVAC is detected, slow-release biocide tablets may be installed in the pan to inhibit mold for the season.   
  • Most portions of residential ductwork are not accessible to the average homeowner. An inspection by an HVAC technician equipped with the proper equipment can identify mold growth inside duct passages. Ductwork cleaning, including mold removal and sterilization of affected surfaces, is required to neutralize contamination.

Your source for a healthy and comfortable indoor environment since 1922, the professionals at Paitson Bros. are ready with effective solutions to handle mold in HVAC components.

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