Mold: A Common HVAC Complaint That Is Easy To Deal With

Mold Removal HVACThe presence of mold in an HVAC system is a common complaint.  Mold is a sneaky little bugger.  It can grow and proliferate and make building occupants sick without ever being seen, and dramatically reduce indoor air quality (IAQ).  And the fastest way to spread mold through a building is through a forced-air HVAC system.

The reason this complaint is so common is that mold is always present in your buildings and your HVAC system to the extent that it is present in your building’s environment.  There will be more mold in humid weather and less in dry weather.  You will never get rid of it completely, but you can control it. All it needs to grow is moisture and food – take those away and the mold goes away.

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According to the U.S. EPA, you should routinely inspect your HVAC systems, not just for mold, but for moisture.   Look at drain and condensate pans to make sure they are draining properly.   If they are clogged, the moisture that accumulates will become a mold factory.  Also make sure that all HVAC ducts and system components such as air handlers, blowers, plenums, and the like are free of any moisture.

How to Get Rid of Mold

Despite regularly inspecting your system, you are still getting complaints about it (mold starts to grow in as little as 48 hours), here are some tips you can share with your HVAC contractor for cleaning it up:

  1. Turn off your HVAC system.
  2. Everyone involved in this cleaning should wear at least an N-95 respirator
  3. Replace anything porous, such as filters or insulation that has become wet.  Double-bag the waste using 6-mil or thicker plastic bags.
  4. Use wet vacuums to clean out any standing water.
  5. Use an EPA registered disinfectant labeled for HVAC use to clean non-porous surfaces (Ductwork, coils, plenums, pans, etc) of mold, mildew, and other dirt. BIOSPRAY-TOWER ready-to-use disinfectant and mold cleaner will kill and remove mold, mildew, and odor-causing bacteria.
  6. Clean the HVAC evaporator coils using a mechanical coil cleaning system to remove any solid debris.
  7. As an added measure, isolate each section of ductwork you clean with bladders so the spores you stir up during cleaning don’t spread to other parts of the system or the building. Fog the area with an EPA-registered disinfectant.
  8. Apply a mold and mildew inhibitor to all components of the HVAC systems. Again, this must be EPA registered and specifically labeled for use in HVAC systems to limit risks associated with using the wrong chemicals and cleaners in HVAC systems.  BBJ Mold Control is EPA registered for use in HVAC systems to control mold growth for up to 2 years.
  9. As a final step, HEPA vacuum anything that you cleaned up.

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57 comments


  • James

    We replaced our 18 year old AC unit with a brand new high efficiency 17 SEER unit. When early spring hit last year, we were bombarded with an awful “dirty sock” smell coming from the vents. We clearly had what I now know is Dirty Sock Syndrome. My installer was good about trying to fix it by installing a brand new epoxy coated coil. Everything seemed fine, but now, a year later, it’s back. They are now talking about have a new coil coated with Bronze Glow. This is supposed to be an even better coating, but I have to say I’m dubious since the first coating didn’t work. I guess we’ll see. From what I’ve learned about DSS, it is caused my mold and mildew that is living on the coils. When the conditions are right (like when the heater is on at night and then switches to cool during the day), the mold spores put off these noxious fumes. My concern is our health. My wife has been sick ever since the cold weather hit here in FL (mid Dec.). I’m really starting to think it’s coming from the AC. Has anyone heard if DSS can cause illness? Thank you.

    February 3, 2021
  • Rahul Rao

    Mold definitely will cause illness even though Allopathic (Western) doctors will never admit it. Your wife may have CIRS, being someone whose genes might be affected (which is why you and other family members don’t have symptoms). Look into doing an ERMI/HERTSMI test yourself from envirobiomics.com. Instead of more coatings, think about installing a UV light on the coils or after the coils. Also install a MERV 16 (almost the equivalent of a HEPA) filter prior to the coils. Check out survivingmold.com for more info and there is an e-book call “Mold Illness: Surviving and Thriving” by Paula Vetter that has really good tips on everything including how to clean your home and you might access that on your computer from your local library for free. If you can afford it work with a naturopathic doctor or an osteopathic doctor who can treat integratively. I’m sorry this is happening to you and hope you get better quickly.

    March 10, 2021
  • Thanks for the info about cooling towers. I need to repair my cooling tower. I’ll look for a professional who can help me with getting the parts I need to fix a cooling tower.

    March 17, 2021
  • Caroline Scott

    Thanks for sharing this step-by-step guide on how to deal with mold in an HVAC system. I don’t think that I could do this on my own though, I seek the help of a professional provider of hvac and plumbing services in Northern Virginia and Washington DC when it comes to these types of problems. I believe that major home appliances must be properly installed and regularly serviced for maintenance by professional service providers to ensure that it would be done right to prevent possible breakage.

    March 17, 2021
  • I had no idea that mold is technically always in your HVAC system. A ton of people might assume that means the pipes are bad. However, I think I’ll still have a professional come look at my system just to be sure.

    April 13, 2021
  • I’m glad you talked about how mold comes with health issues. Recently, I visited my sister’s house, and while I was helping her with some chores, I noticed some mold traces. My sister’s stubborn and said it could wait, so I’ll be sure to share this article with her as soon as possible. Thanks for the information on mold issues within a house’s HVAC system.

    May 12, 2021
  • Thank you for the information re mold in the HVAc system Today I learned from my HVAC PRof that my 9 mo. Old Rheem system is beginning to develop mold. We opted for installing a UV light on the coils. It shouldhelp for a few yrs.

    May 28, 2021

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