Q&A ion Tests for mold in HVAC air ducts.

This article series explains how to assess the level of mold contamination in heating or cooling air ducts, and the aggressiveness of mold testing (do we agitate the ducts) that can form sources of error when testing HVAC systems for mold contamination.

FAQs on Testing Air Ducts for Mold or other Contaminants

These questions and answers about mold contamination or other particle and dust in HVAC ducts were posted originally

at AIRBORNE PARTICLE & MOLD LEVELS in DUCTWORK - please be sure to review the testing, inspection, diagnosis and advice given there.

Question: how can I arrange a test to identify the mold in the flex duct on my HVAC system?

Recently, I discovered mold in the air ducts of my house.

I am hoping you can tell me how to get it tested as I am very concerned.

I will forward pictures as well.

Thanks in advance for your time and help. - A.B. 11/16/2012

Reply: focus on removing the mold (replace the flex duct) and fixing the cause of its growth

A competent onsite inspection by an expert usually finds additional clues that help accurately diagnose a problem - in this case, why the flex duct in your photos is moldy, how much moldy material is present, and thus not just how to correct the problem but how to prevent its recurrence. That said, here are some things to consider:

Testing your HVAC duct mold is easy following the procedure we describe using clear adhesive tape -

see MOLD TEST KITS for DIY MOLD TESTS and use any qualified mold test lab or look into the list of labs and experts we provider at InspectApedia.

BUT I'm not sure I would bother in this case. There are sometimes reasons to test mold or dust samplesbut in this case you'd be best off spending your money on replacing the moldy ductwork and fixing the cause of its growth in the first place.

See MOLD TEST REASONS

1. First, I'm not confident that one or even two economical tests will detect all of the genera/species present nor even the most problematic one - if you want to try anyway, be sure that your tape samples are representative, at least by visual examination, of the dominant mold present.
2. Second, while there are some cosmetic molds (on wood framing) I don't find them in ductwork; and while the dominant molds I do find in ductwork are often allergenic, some genera/species are toxic or pathogenic - in all cases, removing the mold is what is in order, not "magic sprays", or "killing mold" nor sealing the flex duct interior.

In sum,

Replace the moldy flex duct, inspect the whole system for cleanliness, clean components that can be cleaned (air handler blowers, metal ductwork interiors), and fix the cause of mold growth.

See MOLD in AIR HANDLERS & DUCT WORK

and CONDENSATE HANDLING, HVAC and also

see WET CORRODED DUCT WORK for some diagnostic help and cleanup advice when moldy ductwork is a problem.

See MOLD / ENVIRONMENTAL EXPERT, HIRE ? for help in deciding if it's appropriate to bring in an expert.

Question: can you determine by viewing photos of a dark substance on the [outside] of an air handlers' ductwork that there is mold contamination? Can I assume the mold is also inside the ductwork?

Would you be able to determine by viewing the photo DSC 0199 if the dark black substance which appears in two areas of the air handler’s adjoining ductwork is a mold which has formed from condensation? If this is a mold can it be assumed to exist inside the duct where air flow would be exposed to the mold?

All of the filters were found to have excessive dust and dirt build up which would lend itself to introducing particles into the ductwork which could harbor mold spores. - J.B. 12/31/2013

Reply: No.

A competent onsite inspection by an expert usually finds additional clues that would permit a more accurate, complete, and authoritative answer than we can give by email alone, and for the case you describe I'm certain that an onsite expert would be more useful.

You will find additional depth and detail in articles on ductwork mold contamination and leaks into ductwork at our website. That said I offer these comments:

I see in your photos what looks like leaks into and out of a section of ductwork - a condition that indeed invites mold growth. 

I also see thick debris in the other photos - but from just the photos, no honest competent investigator could conclude the extent of mold contamination nor hazard.

The minimum steps that make sense to me are to investigate further to

- find and fix the cause of leaks into the ductwork or air handler or both

- look in the areas of leakage for visible mold growth

- change the filters regularly

- if filters clog quickly, look for an unusually high level source of airborne particulate debris

No you cannot assume that because you see mold on the outside of an air handler, plenum, or HVAC duct that mold is growing inside the ductwork, nor could you assume, even if mold were inside the ducts that it is the same genera/species, as the interior materials and debris that might support mold growth may be different and thus may tend to grow different molds.

More to the point, in tracing mold contaminatin in buildings one needs to follow the water.

If the leak that made stains on the outside of HVAC equipment and ducts also sent water inside the same system then yes, one might want to look at the extent of cleaning needed inside the duct system. But if the leak did not send water inside of the ducts then it would be unfounded to assume that the same mold contamination was present therein.

Reader follow-up: if it's dark it's mold, right?

I do realize it takes a hands on approach and not just a view of a photo taken to establish any extent of mold intrusion. I assume from your response below we cannot even say with any certainty that the dark substance is mold? 

It could be just a discoloration that occurred after the fact from years of operation, however, I cannot imagine what else would cause the discoloration other than mold. 

Reply: No

The dark gray stuff I could make out in the photos could be just house dust.

If you look at some of the photos at InspectApedia of "what mold looks like" you'll see that if mold is actually growing on a surface there are usually recognizable growth patterns, not uniform distribution of debris. On the other hand, if there were a larger mold reservoir in a building, airborne mold spores or other mold debris could be mixed in with dust.

Keep in mind that of the approximately 1.5 to 5 million mold genera/species, only a small subset are "dark" or black, and of those, a smaller still subset are particularly likely to grow in or on building materials, and a smaller subset of those that are particularly harmful. I agree that a dark discoloration, when viewed closely, may contain or even be mold, but dirt, house dust, and other debris are also dark.

Generally for detecting mold growth on a surface one first looks closely at the suspect area for the characteristic mold growth patterns - enabling one to assert that mold is present even without knowing its genera and species. Often this is enough, since the cleanup procedure does not depend on the mold genera/species.

However in some cases, particularly where mold-related illness is involved, the physician may want to know what molds are in the patient's environment.

And in other cases where large, costly mold remediation projects are required, knowing what mold genera/species were being removed combined with pre-testing of various building areas outside the remediation area can head off problems with poor cleaning or inadequate work area dust containment that may arise later.

Reader follow-up: my concern is if the mold I see is entering the HVAC air flow

Yes, i agree, the filter debris appears to be only dust buildup but after Auto correcting the air handler photo it improves clarity and if you zoom in close it appears to be mold for sure. My concern next is to determine if it is inside the ductwork and allowing the spores to communicate with the air flow.

Reply: agreed - take a look inside the ductwork for evidence of water leakage and mold growth

Agreed; I may not have emphasized it adequately before but to me the red flag was what looked like water leak stains running down the exterior surface of the duct, suggesting the chances of leaks into the duct system as well.

If you find mold there and if the duct interior is an insulating mat rather than simple sheet metal, it may be cheapest to simply remove and replace that duct section.

Reader follow-up: I found a website that says ductwork is the most likely place to find building mold

I found another site which appears to mirror the same issue i am having. I would venture to say that the inside of the duct itself has to have some deposits as well. The website states "This is the #1 place that mold is found in your home, outside of roof leaks. This condition is caused by air handler unit that was not maintained properly."

Reply: the quotation is mistaken

The website you quote is interesting but not without conflict of interest and not fully nor accurately informed.

While some of the photos are almost certainly show some mold contamination, one cannot always nor necessarily easily distinguish between debris deposits on a fiberglass duct liner and mold contamination.

Further, some of these molds are very common (Cladosporium cladosporoioides), sticky, not easily airborne, not found at notable levels in an in-duct air sample, and at worst allergenic, and in small areas not actionable.

Other molds less likely to be found but that can appear can be more of a concern (Aspergillus sp./niger for example) as they are easily airborne, small, toxic or pathogenic, inhaled deeply into the lung, may be light colored and difficult to see.

The more reliable approach as a starting point is to track water leakage first, and when looking for what is probably mold contamination look at colors and growth patterns to determine first if there appearst to be mold present at all.

he mold test folks and even some mold labs (not mine) would love it if everybody would keep testing everything quite often to "screen for black toxic mold" which is as I imagine you, more sanguine, understand is inappropriate at best and misleading or worse.

See BLOWER LEAKS, RUST & MOLD

and PARTICLE & MOLD LEVELS in DUCTWORK

and Causes of mold growth in HVAC ductwork - mold in air ducts

and if you like, also see FIBERGLASS INSULATION MOLD which explains that even clean-looking fiberglass insulation may be mold contaminated.

Photos of what mold looks like on various surfaces are

at MOLD APPEARANCE - WHAT MOLD LOOKS LIKE

and at MOLD APPEARANCE on VARIOUS SURFACES

Reader follow-up: I still think the air handler ductwork is the most prone are for mold incubation

Your website is the most informative of any I've found to date. I do think though that he is claim about Air handler ductwork just like mine is the most prone area for mold incubation.  I havent found any other ductwork at least from the outside appearance that has the same black color.

Reply: Drywall and wood and perhaps carpeting are the most mold-friendly and largest surfaces areas in buildings likely to product a wide range of mold contamination reservoirs of a wider range of mold genera/species

Regarding your observation that ". I do think though that he is claim about Air handler ductwork just like mine is the most prone area for mold incubation."

That statement is mistaken and cannot be based on building science, mycology, nor broad field observation of buildings.

From education in those fields, from literature review of studies of building mold occurrence, and from direct experience in evaluating close to 5000 buildings over more than 30 years, including directy studies of every material and surface in mold-contaminated buildings to map the preference of various building molds for specific building materials and surfaces, it is readily apparent that the claim that ductwork is the most mold-prone "incubation" area in buildings is considerably off the mark.

Enjoying the freedom of un-edited website publication, that statement is an opinion, and it is wrong, and remains unsupported by authoritative citation nor research.

Even the word "incubation" suggests a lack of knowledge of mycology.

The largest mold reservoirs in buildings that have suffered water damage, leaks, or on occasion just high humidity are found on the most mold-friendly materials, particularly the paper surfaces of drywall, and secondarily on exposed wood surfaces such as framing and sheathing.

Unlike ductwork, those surfaces harbor most of the 200 common mold speciesas well as occasional occurrences of less common molds and include the more harmful mold genera species regularly found in buildings such as Aspergillus sp., Penicillium sp., Stachybotrys chartarum, Memnoniella echinata, and yeasts.

See MOLD FREQUENCY in BUILDINGS for details.

We do not find those genera / species growing in ductwork in large reservoirs if at all, though we do find them in contaminated dust entering the duct system from an infected building.

The surfaces of HVAC ductwork in buildings are typically of three materials: plastic, metal, or a coated dense fiberglass mat. While we can find mold genera/species that will grow on just about any material, none of those three comes even close to the mold-conducive friendly environment provided by drywall, wood, wallpaper, even carpeting.

Of the approximately 200 mold genera/species most frequently found in buildings, only a very few of them, particularly in the Cladosporium group, are commonly found in HVAC duct systems.

I explained the comparative risk levels using two common Cladosporium findings vs. Aspergillus sp. (not commonly found in ductwork) at a gross level in my earlier comments. In short, the most harmful and most easily airborne molds are not commonly found growing inside HVAC ducts. When such molds are found inside HVAC duct systems, in general they have arrived there in air circulated into the duct system from a larger, more dangerous building mold reservoir.

Having disposed of the "bad mold is mostly in ductwork" mistake by pointing out what does and does not grow in ducts, one has but to observe further that the level of mold hazard in a building depends on both the mold genera/species that are found therein, and on the size of the mold reservoir itself.

In a simple comparison of the total indoor building area represented by drywall and wood in most buildings (in North America, Europe, Australia, New Zealand and the U.K. and parts of Asia) with the total area that might be represented by the interior surfaces of HVAC ductwork in that subset of buildings that even have ductwork present makes clear that the potential contribution to building mold contamination by ducts is small compared to the potential contribution to building mold from the significantly larger mold reservoirs of of other materials and the larger range of genera and species of mold that they support.

This is not to say that there is never mold contamination in HVAC systems

. It is to emphasize that across a population of mold-contaminated buildings where professional mold cleanup is justified and appropriate, by no means is the ductwork mold reservoir the largest, by no means is it the most conducive to mold growth, and by no means are the mold genera species found growing therein the most harmful.

Question: interpreting mold levels in air ducts

(Feb 23, 2015) Veronica said:

First of all, thank you for all of the incredibly helpful information on this website. I recently had an air quality test completed (I've been having extremely bad allergies and other unexplained health problems since moving into this residence and using the air conditioner.).

The company tested the air quality in our living room and found essentially no mold in that air sample. They also stuck it into one of our air vents and took an air quality sample. The sample from the air vent has Chaetomium (raw ct: 121; spores/m3: 1,600) and Peniccillium (raw ct: 30; spores/m3: 1,600).

Are these numbers concerning? Also, if the ducts are too old to be cleaned and would essentially fall apart, would it be best to replace the air ducts? Thank you in advance for your advice.

Reply:

Veronica

Even relatively low indoor spore counts in air *might* be significant - depending on test conditions and building history. It's not the case that problem mold from even a significant reservoir of mold in a building is always readily observed in building air.

Water-related molds such as those you cite are suggestive that something has leaked and that there is or was an indoor mold reservoir. But ultimately the interpretation of your numbers is

1. unreliable as a single measure of mold contamination - a thoughtful inspection of the building and case history are essential

2. need to be interpreted by the person who inseected your building - otherwise the data is not helpful.

On 2018-11-17 by (mod) - success using an organic plant based cleaner to kill mold

Thanks for your opinion statement Linda.

If you can point me to any facts-based or science-based research on the surface cleaner you used that would be helpful.

Bottom line: NO surface spray or treatment is an adequate remedy for mold contamination in buildings; you need to remove the mold and fix its cause.

Just spraying a surface can

- leave a significant mold reservoir in a building wall, ceiling, or floor cavity that can affect the building's occupants

- leave non-viable "dead" spores that still contain mycotoxins - thus remain harmfjul

- leave viable spores

- doesn't address hidden reservoirs

I agree that it's rarely necessary to throw away items that can be laundered or dry cleaned like bed sheets and towels.

Still we're glad to hear from you as long as you don't post advertisements - which is why you don't see the other messages you posted here recently.

To protect reader trust we do not sell nor endorse any product nor service.

On 2018-11-17 by Linda

My sister had mould issues in her rental home last year

You could smell it as soon as the front door was opened and it was visible on the blinds, furniture, clothes, walls and ceilings. She was always sneezing and her husband had breathing issues so we decontaminated the house with an air steriliser then we wiped all surfaces clean, including her clothes and shoes. We then used an organic (plant based) surface cleaner, that prevents mould

. It took a long time but was worth it. By the end of the day all visible mould was gone and we could no longer smell any mould either - only a natural clean smell. Her rental remained mould free and clean smelling for months until she moved to her new home. She no longer sneezed everyday and her husbands breathing also became easier. Anything mouldy (sheets, clothes, carpet etc) was cleaned so we didn’t need to throw anything away.

On 2017-10-23 by (mod) - creepy crawly fibers on skin - read about Morgellon's Syndrome

Anon

It's difficult to propose a repair action for unidentified little white things in dust - particularly since little white stuff may be perfectly normal house dust comprised principally of fabric fibers and skin cells. So you might want to start with having a forensic lab examine a representative sample of settled dust collected on clear adhesive tape.

That lets you identify the dominant particles that in turn can point to an abnormal dust source by particle type and color. (such as fiberglass insulation in damaged fiberglass insulation lined ducts).

You should absolutely start the investigation with your own medical doctor, asking what indoor environmental things might cause or exacerbate your complaints - those can then be targets for investigation.

Avoid hiring someone to do an arbitrary "air test" - such tests might, if you're lucky, be diagnostic (saying yeah there's something of concern here) but

1. such tests are not prescriptive: you have to pay all over again to find the problem source and to specify what cleaning and repairs are needed
and

2. a "negative" (nothing found) air test result is not reliable - search InspectApedia for AIR TEST RELIABILITY to read details.

Please be sure to read about your symptoms and similar complaints found

at MORGELLONS SYNDROME

On 2017-10-23 by Anonymous

@Jamie,
Hi Jaime and Thomas or anyone else with advice! Jaime I'm Just wondering if you ever got a reply on your msg??

I'm dealing with a very similar issue and was wondering what the outcome was for you? I have a 3 year old and we are renting as well. We've have had the craziest symptoms long story short and I thought I was losing my mind.. I definitely think all of our symptoms are mold related however. Can u tell me, what u did fix it?

Can u describe the little white/clear dust like things you expirienced too please!?? I have them EVERYWHERE .

They've traveled through all my clothes, car, bedding carpet Everything! I can't find much on the internet besides parasites and mold.. whatever they are they travel quick. Nothing seems to kill them, and they spread insanely quick! I thought they were bugs at first, then mites..sometimes particles etc.

But i still havent figured it ou S They bite/sting/poke (somehow) and they are most active at night between 8m-5am ish.

There's an abnormal amount of particles floating in the air, my car and when I shake my clothing or even swish my skin. I've never had this happen! I'm not dirty or weird I'm a normal 26 yr old single mom which is why I'm losing my mind having not been able to rid these things!

I've tried everything And since I'm renting I can't go tearing the house apart like I wish I could. I'd do anything to rid this issue. It has infested my entire life. I lost my job between the both of us being sick constantly,

I havnt slept well in months as they are craziest at night when I'm trying to sleep! Excessive tiredness like I could sleep all day and still Be tired, my brain feels clouded and having basic memory issues, that I've never had before and some other issue etc. I've spent mt entire income on cleaning supplies, sprays, Hotels rooms and new clothing trying to figure this out..: . My fam and friends think I'm crazy,which made me question my sanity for a while but it's definitely real 💯
did u ever expirience any of these weird symptoms??

Crawling/needlepokes, itchy infested clothing bedding car etc. headaches, persistant sinusitis, stuffy nose, sore throat, nausea, wheezy/cough, bodyache, random sore gums (never have had prior), I have a tiny red blood spots all over. And I mean tiny, as if I used a needle to prick myself..everywhere! I feel it when it happens too.. I'm basically living in hell at the moment so if anyone has any advice I'd greatly appreciate it!! Best Regards,
Savanna

On 2017-08-20 by (mod) - friend was going to help remove toxic mold

Thomas,

If you had demolition and debris and dust and dirt scattered about the home by heavy-handed and slug-footed workers,

1. do not make any payments until your concerns are addressed

2. have an independent assessment of the cleanup needed: washing, vacuuming, HEPA vacuuming, damp wiping surfaces, etc. and of any damage that may be revealed after that cleanup

3. photodocument everything

I can't say that anything is ruined vs. needing cleaning - from an e-text one can but guess.

On 2017-08-20 by Thomas

My friend was going to help remove toxic mold by tearing out a 9ft bathroom cabinet with two sinks.

They were supposed to cut out the outside wall it was on and have the bathroom sealed off from the rest of the house. Instead, they took everything through the bedroom, and walked all through the house. Is the floor ruined.What about Persian rugs. Tile, and fake wood floors.? Help! I'm feeling so frustrated. I don't know what to do..

On 2017-07-21 1 by (mod) - wet moldy carpet and padding can't normally be clean ed and are tossed oout

Lindsey,

Carpet that has been wet and actually moldy, or similar carpet padding, get tossed out as those can't be effectively cleaned.

But if your carpet was never wet and is not actually growing mold, then HEPA vacuuming it, while it won't remove everything, should reduce the surface dust that might be moldy. I'd give that a try.

Beyond that you'd need to perform a vacuum test on carpeting to see how much moldy dust it retains.

Frankly if I had severe dust allergies I'd prefer not to live with wall to wall carpets in any case.

See CARPET MOLD / ODOR TESTS

found by using the InspectApedia.com search box to look for "CARPET MOLD TEST"

On 2017-07-21 by Lindsey Hansen

I moved into my apartment in November last year. In December I started getting crazy hives and swelling that sent me to the ER 4 times since December. The hives would come and go but I always had sniffles. I went to an allergist and was told I had severe mold allergies and fungal sinusitis.

Since then I found massive amounts of mold in my ducting and was wondering if I need to completely remove my carpet since it has had prolonged exposure for 9 months?

On 2016-11-12 by Donald Lee

I recently moved into a rental house (April). I immediately began smelling the most God-awful stench coming from the air vents whenever the system is activated. The stench is truly hard to describe; it smells like a combination of stinking odors: something dead and putrid, sewage, and a stale, fetid odo

r. Although I haven't ruled out the possibility that it could be vermin, (dead rat, etc...)somewhere in the duct work, I'm more inclined to believe that it is mold, simply because I found out that the previous tenant had the same problem and any vermin would have decomposed by now.

My question is, does any kind of mold produce such a stench? I would appreciate a reply if anyone has an answer.

On 2015-10-17 by Jamie

I have mold growing in this house im renting, just moved in. I am pretty sure its causing problems with me my husband and my 16 month old daughter.

I have 2 big grate vents in each side of our hallway and in floor heating vents in every other room, i have been finding what looks like white and sometimes clear appears to be dust.

I am worried and i know somethings is up we have been here 16 days and already have severe head aches, a weird smell which we thought was because our home is heated off an oil drum not gas, and we all have rashes, weve been forgetful short term wise, who do i call i need to fix this!! I live in alaska. Thank youfor your time!

...

Continue reading at AIRBORNE PARTICLE & MOLD LEVELS in DUCTWORK or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• BLOWER LEAKS, RUST & MOLD explains causes of leaks & mold in HVAC ducts
• DIRTY A/C BLOWERS includes leaks, rodents, & mold in air handler units
• DUCT CLEANING ADVICE
• FIBERGLASS AIR DUCT MOLD TEST
• FIBERGLASS INSULATION MOLD - home
• AIRBORNE PARTICLE SIZE DEFINITIONS & TYPES
• See TAPE & BULK SAMPLING & TESTS for MOLD for details of how to use adhesive tape for surface sampling of dust, particles, or suspected mold growth on building surfaces.
• TEST CHOICES for MOLD in FIBERGLASS
• VACUUM TEST INSULATION CONTAMINANTS
• Also see WHITE MOLD PHOTOS
• WHY DOES MOLD GROW in INSULATION? that includes photos and test results examining suspected mold on the surface of fiberglass-lined HVAC ductwork.

Suggested citation for this web page

AIRBORNE PARTICLE & MOLD LEVELS in DUCTWORK FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ENVIRONMENT

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