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, make building occupants sick without 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. If you are an HVAC professional, consider checking out our six steps to removing mold in HVAC systems article.

Is mold in your HVAC system bad for you?

Yes and no. But it is a common complaint. This complaint is so common because 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. Mold needs three things to grow. Warmth, moisture, and food – take those away, and the mold goes away.

When mold, especially types of molds like aspergillus niger, or black mold, overwhelms systems, air quality can be dangerous. Those with sensitivities to mold can immediately become affected, with respiratory issues presenting immediately. Others, with little or no sensitivity, may notice odors or become more sensitive. If really bad, you will notice that mold spreads to other surfaces.

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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 the drain and condensate pans to ensure they are draining properly.   If they are clogged, the accumulating moisture will become a mold factory.  Also, ensure that all HVAC ducts and system components, such as air handlers, blowers, plenums, and the like are free of moisture.

How to Get Rid of Mold in Your HVAC System

Despite regularly inspecting your system, you are still getting complaints about the smell (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. If vacuuming “dry” coils, use a HEPA vacuum.
  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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  • 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 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 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
  • 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
  • Wndyb1654

    We just discovered mold on our ducts, but we had new ac units installed, but they never told us there was mold. They were installed October 2020, but when we went to get our air ducts cleaned he discovered a large amy of mold June 2021. Could it have grown from those period of time, plus our house is being renovated. So ac is turned off and on.

    June 29, 2021
  • Donna

    I have contacted several HVAC companies and can not find one that will clean/spray coils for mold. They all just want to sell you a UV system. Has anyone found a company that does this?

    August 8, 2021
  • Penelope

    I’m surprised at your comment that ‘western’ doctors won’t admit to illness caused by mold. I have never found that to be the case. My GP has made an appointment for me with a pulmonologist and my neurologist suggested that my headaches might be caused by mold after I discussed the possibility with her.

    January 21, 2022
  • Leah Zastrow

    But it is a true statement. I have had mold toxicity for 35 years from living in houses with mold and now working in an office environment with dust and mold. i have communicated this with my doctor and all GP’s do is shake their head in disbelief because they are narrow minded and and believe what was taught to them in outdated text books. they cannot cash in on treating mold toxicity. It is disgusting actually.

    March 13, 2023
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