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Managing Mold-Part 2: Tips for HVAC and Filter Maintenance

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By: Linda Barlow, freelance writer  |   03.31.14

Even if you haven’t had a mold problem in your building, you’ve certainly seen the headlines. Homes, schools and other public building shuttered and deep-cleaned to be rid of the black menace that some blame on health issues ranging from mild respiratory problems to debilitating illness. Here’s what you need to know to keep your HVAC system from becoming a breeding ground for mold.

Mold is virtually everywhere. It travels into buildings through open doorways, windows, vents and HVAC systems. It can also be carried indoors, attached to clothing, shoes, bags and pets. Small mold spores (smaller than 5 microns) are more likely to be removed the HVAC system and other ventilation methods before settling on surfaces. And larger spores, once settling on surfaces, can mix with other dust and become re-suspended in the air when building occupants move about. 

While HVAC systems and air filters can remove microorganisms such as mold spores from the indoor air, they can harbor them as well, especially if proper maintenance procedures like regularly scheduled filter change-outs are not followed. Proper filter maintenance is crucial to keeping HVAC ductwork clean. If dirt accumulates in the ductwork, and if the relative humidity reaches the dewpoint so that condensation occurs, then it can become a breeding ground for bacteria and mold. 

Here are some tips for filter maintenance to help reduce the opportunity for mold growth:

  • Size filters properly and fit them well into the HVAC system’s filter rack to prevent unfiltered air from bypassing the filters and entering the occupied space.
  • Replace filters regularly – every three months or as recommended by the filter manufacturer.
  • Check filters regularly for dampness.
  • Change filters immediately if they become wet or if microbial growth on the filter media is visible. 

Other HVAC system maintenance recommendations include:

  • Monitor outdoor air intakes and inlet airways for intrusions of rain, snow, dirt and leaves.
  • Keep air conditioning drip pans clean and drain lines unobstructed and flowing properly.
  • Use sloped drain pans with drains at the low point.
  • Make inner surfaces of the air conveyance system of materials that are impermeable to water penetration and easy to clean.
  • Provide easy access to coils, drain pans, and the downstream side of cooling coils for inspection and cleaning. 

The U.S. Environmental Protection Agency cautions against running the HVAC system if it is known or suspected to be contaminated with mold. The EPA also recommends using “high-quality” air filters during any mold remediation activities and changing them regularly during remediation as well as following.



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