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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  • I am a heating contractor in Chicago Illinois and I run into this problem a lot in the hot muggy summers here. this is a lot of good information for the remediation of mold but it seems like a lot of these things listed are a bit above what a homeowner is capable of. Unless you have some sort of hands on mechanical experience you will not be able to accomplish such things like checking the condensate pan and checking the ductwork for moisture. This seems good checklist for a flood type situation with minimal water damage. One thing that I wnated to add where I see a problem is in humidifier pads. These pads rarely get changed by the homeowner, when they need to be changed every season. What I find is that these pads get so moldy that you actually start to get bad odors in the home and not know where they come from. I recommend that homeowners should change these pads each season and wash out the holding tray for the pad with bleach and water. Also check the drain hose and inspect for mold, i am always surprised by how much they get colgged up and filled with mold. These are some Humidifier Tips that I give my Chicago customers and I find it gives good results.

    November 12, 2009
  • Goodway Blogging Team

    Mr. Gremillion raises an excellent point. Our primary audience at Just Venting consists of HVAC industry professionals. As he pointed out, a professional contractor would have knowledge and experience that we wouldn’t expect a homeowner to have. Areas such as humidifier pads and condensate pans aren’t something you would expect a homeowner to think about it or attempt to clean.

    This might actually be an opportunity in disguise. Consider talking about it with your customers — residential AND commercial, when you go on service calls. Maybe you can even design a basic maintenance or “mold prevention” program to sell them, much like the pre-season furnace checkup offers you see before a freezing cold Illinois winter rolls in.

    Rich Silverman
    Goodway Blogging Team

    November 12, 2009
  • Len Douglas

    can fluorescent lighting be used to treat mold in air handler and can it be self installed where can these be located my hvac co. wants to install for 1200.00! thanks

    January 13, 2011
  • Tim

    I’ll defer to your HVAC pro on this one. If you’ve got mold problems, then there are a variety of solutions, including biocides and yes, “newer” light based technologies. If you’re not comfortable with the quote, contact a few different installers and ask them for their input. Might be surprised at the options.

    May 5, 2011
  • […] water combined with dust and dirt within your ductwork create a breeding ground for spores to grow. Take immediate action with these […]

    May 7, 2013
  • A mold treatmen expert ought to be hirted at the
    first signs of mold. When this takes effect it’ll produce spores into the air.

    The Dupli-Color TV video is inspirational.

    December 15, 2013
  • But besides cost benefits, you have to find an LPG provider that offers exemplary
    service. Therefore, early diagnoosis and treatment is essential for a healthier home.
    Firstly, clean annd identify any infected places.

    December 16, 2013
  • […] may form condensation, proving to be the perfect breeding ground for fungi and mold to develop. Molds can be easily carried in through dust particles and their spores pose a danger to your health if they are inhaled. […]

    June 23, 2016
  • vernon kingery

    How valuable is an uv light 1002 system in an
    3500 home ac? Do you really need it? Also
    should I put storm surgers on it? What Is normal cost of buying and install? How much should a home duct system special plastic black insulated polymer made for outdoor weather and heat cost? Approx. 40ft.

    July 28, 2016
  • A mold treatment expert ought to be hired at the
    first signs of mold.

    October 30, 2016
  • […] Mold is an allergen. Its impact on a person’s health depends on how extensive the mold is in the home and the person’s sensitivity to the mold. At minimum, people experience weakened immune systems from mold. The body recognizes mold as a foreign body, and it goes quickly to work to get rid of it. This makes the immune system work hard. This is why people end up feeling tired. This also causes people to be more susceptible to other sicknesses. […]

    October 31, 2016
  • John

    I live on the coast of North Carolina where it’s very humid doing the late spring , all summer and early fall !
    The AC guy told me that He could installed a light would omit the mold forever . The labor and material would cost $350 to omit the mold ! I was wondering IF anything else out there to omit mold !

    November 3, 2016
  • A proper maintenance can prevent molds like this. It’s much better to prevent.

    November 12, 2016
  • Lisa

    I have a question… i live in an apartment and staying sick.. all i smell is mold mildew… apartment is only 2 yrs old…
    Question.. my ac/heating unit is always sprayed with the sprinklers.. would this be an issue??

    November 28, 2016
  • Stephen Buzzell

    Mold is dangerous not important to most folks just sick or dying folks.

    December 2, 2016
  • Unfortunately we see this often here in St Louis because of our super humid summers. Families get sick and are in the hospital for breathing problems and little do they know its simply their AC at their house causing the problems. Just do regular maintenance to the system and everything should be good for the most part.

    December 2, 2016
  • louis collado


    December 16, 2016
  • sandy garbrandt

    we just purchased a new house only 3 years old and its out summer house so were not always there ,but I got really bad allergies thought it was a cold but my husband says he smells something in the house and he has a headache and nausiuos,we r in a panic what should we do?

    January 4, 2017
  • Tim

    We would suggest contacting a certified contractor who handles mold and mold remediation in your area to have them come out and completely check the house.

    February 2, 2017
  • Tim

    If you are referencing your outside unit, the answer would be no. I would contact a licensed HVAC contractor to check your air handler(s). a good cleaning may be all they need, but they would be able to diagnose other problems.

    February 2, 2017
  • Tim

    He’s probably referring to a UV light system, many of which have shown to help with mold issues. However, the best way is to make sure that the system is properly maintained, often.

    February 2, 2017
  • Chris

    I paid about 2k two months ago to a duct cleaning company for green mold removal from my hvac coils and pads inside the unit and all 20 vents with antimicrobial chemicals. Required two visits and staying out of the house for several hours each time. Had a mold inspector in yesterday and there’s mold again in the unit and dirt in the vents. Humidity in the house usually in upper 50% range, as high as 70%, never lower than about 40% Aside from what may have been shoddy service by the duct cleaning company, I am wondering if a hvac dehumidifier might work to reduce humidity in the hvac unit and house. I have a Lennox system, one inside and the other fan outside the hous . Not much knowledge on all this but I know I have to reduce humidity to keep mold away. Any ideas???

    February 7, 2017
  • Dwight Stewart

    I am looking to clean my blower coils on the AC and disinfect the whole system and have the Plenum Box Mold controlled. What could this cost me? Can you respond quickly – thank you.

    February 15, 2017
  • Oh sure...

    You know, I hate it when knuckleheads say “oh, please reply quickly”… Like the world is at beck and call. Try researching yourself…….

    June 4, 2017
  • Heather

    I have found myself googling mold issues in mobile homes and ended up here. I too, live on the coastal side of NC and own a single wide mobile home. For some reason, im having a very hard time getting rid of mildew issue in the middle bedroom of my home which so happens to be my 1 year old daughters room and her toys, bedding, and furniture are growing mildew or mold. I have a dehumidifier which fills up quite frequently. (every other day I have to empty it) I don’t know what the problem could be other than my vent system. How would I get rid of this problem? Would a heating and air company be able to help? I just need advice!

    June 24, 2017
  • Rayanna

    We are having a house built and the hvac guys put the furnace and ductwork in before the roof was on. It was just boarded up but gaps between roof and front and back porches were wide open length of house. It rained and ducts filled with water. The want to still use the insulated flex duct and refuse to remove the foil wrap that is around the metal ducts. The water will never leave them since they are foil and plastic sealed. We are concerned for our health and the health of our home. They aren’t concerned and seem oblivious or ignorant to the issue of toxic mold. What do we do? Oh our hvac guy said he was done when code guy said they had to replace the flex ducts after manufacturer said they needed to go. Very upsetting situation.

    September 17, 2017
  • […] pans are working properly. Air handlers, blowers, and plenums should be free of moisture. An HVAC-labeled disinfectant can be sprayed on non-porous surfaces, such as ductwork, coils, plenums, and pans to get rid of […]

    September 22, 2017
  • Todd

    I live in a new apartment building (3 years old and 1st tenant in) that has Amana heating/ac units in the living room and bedroom. I was never told anything about cleaning them other than just vacuum out the filters occasionally. This time I noticed mold on the vent and got a flashlight to look inside and also found mold on the blower fan, how do I treat this since I can’t remove it?

    October 24, 2017
  • The question about using UV lights in duct systems is a good one, and gets brought up often, The costs to install are high, so research is definitely warranted. The devil is in the details, as is most solutions related to mold. UV light is known to kill mold but only spores that sit directly under the light for an extended period of time. The time varies by mold species. Putting moldy items in the sunshine will have a similar result. But back to duct systems… so UV lights can be effective when the goal is to kill mold on the coils and that is where the light will shine. Know that mold growns on dirt and dust which ends up on the coils and in duct systems, so eliminating the dirt and dust will also keep mold under control.

    The UV lights that are sold to kill mold in moving air, will NOT work, according to my research. Since for UV lights to have an effect on mold spores, ‘dwell time’ is required. Since moving air past a UV light in a duct system will be usually moving very fast, there will not be enough ‘dwell time’ to have any effect on the mold spores being carried. So to answer the question, Yes, UV does have an effect on mold spores over time and NO, UV lights will NOT have any effect on mold spores in moving air.

    June 5, 2018
  • Allison Ray

    There has been a mold oputbreak in my college dorm floor. We have been keeping AC boundaries and windows closed, the air ventilkation on medium and dehumidifiers have been placed in most rooms. It only seems to be getting worse especially with the humidity in Connecticut. Many people are getting sick and their clothes are being overtaken with the mold. Does anyont have any advice on what to do if you live in the area where the mold is? We have been cleaning non stop yet it reappears everyday and we fear there is no way to fully solve the problem unless the contractors get started on their end.

    September 18, 2018
  • Dani

    Hi my husband and I just moved two months ago because we found black mold in our closet at our last apartment. Yesterday I had an incline to do some digging because I had a bad feeling and when I climbed up to the bathroom ceiling and looked through the vents they are totally black/dark grey and spotted inside. Only the bathrooms are like this and the living room has black spots on the flap of the vent but the inside part is still white and all the others on the inside are white but the bathroom one are black. Help! Is it reasonable to think an apartment complex could fix this properly and safely without getting spores everywhere??? When the air kicks in are we breathing in mold? I worry about my dog who stays home alone while we’re at work I do t want him breathing that in all day long. We’re are contacting the apartment complex tomorrow.

    November 5, 2018
  • Jim

    Our main ductwork has insulation inside of the sheetmetal. It is full of mold. Short of replacing it, how can I kill the mold?

    October 10, 2019
  • Aaron Reyes

    Wow, so nice blog, especially I really appreciate this & hope it will be more useful for all. Well, I also know that some other companies have provided such a fantastic cleaning service with a proper cleaning kit as “FIFTY REASONS” so I would recommend this for people.

    December 20, 2019
  • “Mold factory” is right. We serviced a customer recently that had ignored the issue for too long.

    January 9, 2020
  • […] Here are the components that professionals center on during the cleaning of your HVAC unit to boost your mold prevention efforts. […]

    March 24, 2020
  • Air Conditioning Unit and Ducts – Moisture can build up in your AC system, and the circulating air spreads mold spores quickly throughout the rest of the home.

    March 25, 2020
  • It is definitely a very comprehending and nice blog regarding how the ac service is done and maintained. I want to add that I have been facing a Low refrigerant issue. The refrigerant is the stuff that your air conditioner uses to remove the heat and humidity from the air in your home or business. Suggest us what to add on regarding this consequences to get ahead of these discrepancies.

    June 23, 2020
  • Jason

    My air handler?(box with air ducts connected) sweats whenever ac runs. Air duct where it touches the box sweats outside. Recently I smell something funny. Not sure what it is in some rooms. Does the sweating cause mold?. the box is in the attic as well as air duct. I am dallas. Humidity in the house around 59

    June 29, 2020
  • Melissa morris

    We just bought a house that is full of black mold the roof the walls the everything should it be the whole house be gutted what needs to be done

    July 12, 2020
  • Tim

    We recommend contacting your insurance company, and then a remediation professional immediately.

    July 14, 2020
  • A mold treatment master should be recruited at the primary indications of mold. mold is risky to not imperative to most people simply debilitated or kicking the bucket people.

    September 7, 2020
  • Below are a few key signs of mold and mildew growth in your HVAC system:
    – Strong smell or musty odor.
    – Visible mold around air ducts or intake vents.
    – Noticeable leaks or puddles around the HVAC system.

    September 8, 2020
  • I should have read this article a long time ago. I’ve been dealing with this issue for the longest time. Thanks

    September 17, 2020
  • I am looking for this kind of site and thank goodness I found it.It really helps me a lot.I will bookmark your blogsite so I could read more. Thanks!

    October 15, 2020
  • I never thought of those tips you just mentioned. Thanks for this helpful article.

    October 15, 2020
  • jack smith


    October 23, 2020
  • Great Post! This is very helpful and informative article. Thanks for Sharing such a great post. Keep Posting!!

    October 27, 2020
  • jack


    October 28, 2020
  • sae


    November 4, 2020
  • Frank

    This is great information. We live in an older high rise building that uses convectors for each room of the home. The building decided NOT to change the filters for over a year. As a result, dust built up. In fact, the mold was so bad that I started to develop hives.

    I highly recommend contacting a professional that the first sign of mold. An experienced HVAC person will know exactly what to do.

    December 29, 2020

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