Tests for mold in HVAC air ducts: this article 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.

How should I test my heating or cooling duct system for mold contamination?, Levels of Mold in Heating or Cooling Ducts as Sources of Error in Indoor Mold Tests - what causes variation when testing ducts for mold contamination?

This document is a brief tutorial which provides information about the accuracy of and sources of errors in tests for the level of allergenic and toxic mold in residential buildings:Are spore counts valid? Are cultures and swab tests valid?

How to Test Air Ducts for Mold Contamination

Question: what is the best way to test for mold in the heating/AC system

Thanks for your website - it is truly a public service.

My husband and I are both very ill - my husband has recently been diagnosed with metastasizing melanoma in his eye, which has spread to his liver and spine - his prognosis is not good.

[Click to enlarge any image]

I have been sick with sinusitis for over a year now and am known to have severe allergies to mold (causing recurrent bronchitis and sinusitis).

After many scans and tests, my doctors feel the most likely reason not responding to treatment (many courses of antibiotics and sinus irrigations) is because of an environmental allergy.

Because of my husband's illness, we decided we had to move into a more maintenance-free living situation and bought a townhouse a year ago.

Because of my known allergy, and because of a small area of what looked like black mold (and smelled unbelievably vile) discovered during the renovation, we had two different mold remediation companies as well as an air quality testing company come in.

They felt the black mold was removed completely (under negative pressure and other precautions) and then they did a fair amount of preventive work - since there were a few tiny areas of green mold in the basement and attic.

Air quality testing afterwards supposedly showed no mold anywhere.

We recently discovered our front-loading washing machine is one of the brands known to have major mold problems and there are now several class action suits against them.

We had several puzzling episodes of moldy sheets, which weren't recognized until our son came home to visit (my sense of smell has been wiped out by the sinusitis and my husband never had a good sense of smell).

We couldn't figure out how this was happening since we are very careful not to leave wet clothes/linens lying around or in the washer.

According to our son, the mold smell permeated the master bedroom. We then moved to the other bedroom and the same thing happened again, discovered when our son was visiting again, and again the smell permeated the room.

The washer is in the master bath.

I first got sick in our old house (which was a house that, up until then, had been a very healthy environment for me) after we bought the washing machine.

We had a couple of episodes of moldy-smells in our wash in the old house, but I was still able to smell and threw things out right away, but was puzzled as to why they were occurring.

We have replaced the washer, aired out the rooms, bought air filters, have an HEPA filter on the return heating duct, but I am not feeling better (after having rewashed all our clothes and bedding.

We're concerned that mold could be in the heating/AC duct system.

We've thrown out all our linens twice now (after our son discovered the mold) but before we learned about the washer.

We're also wondering if we need to throw out everything again.

My basic question is what is the best way to test for mold in the heating/AC system and is there a company/person you could recommend to do this work?

Thanks for your time and any advice you can give us. - K.J., New Jersey

Reply: A combination of Steps can Help Assess Mold Contamination in an HVAC System

What makes sense to me is to take the following mold inspection and testing steps if you have not already done so:

• A visual inspection of the air handler, 
  
  return and supply plenums, visible areas of ductwork for evidence of leaks, dirt and debris, visible mold, insect debris, etc.
  
  I worry that it's too easy to "decide" that we have a mold problem in one specific place without an adequately thorough inspection and taking of the case history.
  
  The result is the unnecessary expense of having to keep bringing back cleaning or testing people to the property. If we can do so, it's less costly to do it right the first time.
• A tape sample test of a clean newly installed air filter 
  
  after it has been in place for 2 weeks to a month in your HVAC system - a procedure is
  
  at TEST KIT for DUST, MOLD, PARTICLES: INSTRUCTIONS - you can use any qualified mold test lab (Please don't send us your mold sample.
  
  If you cannot afford mold sample processing, CONTACT us and we'll try to help.) This presumes you have a centralized air filter in your duct system or air handler.
• A tape sample of debris accumulated on the central air return register grille 
  
  and on a dusty supply register grille sample too.
• A tape sample of suspected mold growth on the HVAC duct interior
  
  If visible mold is observed inside the ductwork it may be useful to collect a tape sample of that as well, but beware that a modest amount of Cladosporium sp. (several species) is very common where condensate blows around in the duct system, and may be visible, but may by no means be the significant problem in the building.
  
  As we note at BLOWER LEAKS, RUST & MOLD:
  
  While Cladosporium sp. is the most common mold found on earth and while it's just about everywhere, for some people this is an allergenic mold.
  
  We don't want it being blown around by our air conditioning system nor its growth improved by mis-handling of HVAC condensate.
  
  See MOLD CONTAMINATION LEVELS
  and
  
  see MOLD ATLAS & PARTICLS LIST for a description of the health effects and air quality complaints associated with various kinds of mold.
  
  Don't let the discovery of a very common mold throw you off the track of a more careful and more broad inspection.
  
  Make sure you are finding and focusing on the "right" mold problem.
  
  Attention to "toxic black mold" may have been warranted, and media attention often focuses on "black mold", but be warned that there are plenty of harmful molds of other colors, or even "no color", some of which are smaller and more easily airborne (e.g. Aspergillus sp.) than some of the popular "toxic black molds" (e.g. Stachybotrys chartarum).
• A tape sample of settled dust from a room 
  
  where you spend the most time
• Air testing for high levels of mold 
  
  or other troublesome airborne particles is useful as part of a more broad investigation that includes the items above, but used alone it is very unreliable, in that a negative result could be just wrong, and even a "positive" result (mold was found at high levels) is not diagnostic - it doesn't tell us where to look nor where the problem - if one is detected - is located.
  
  See MOLD TESTING METHOD VALIDITY

• Dispose of moldy HVAC ducts that cannot be cleaned
  
  While you shouldn't have to throw away smelly sheets or bed linens nor similar items that can be laundered or dry-cleaned any more than you need to throw away a ceramic dish that can be washed, significantly-contamiated fiberglass-lined HVAC ducts should probably be replaced.
  
  Watch out: attempts to use mechanical cleaning of fiberglass-constructed or fiberglass-lined HVAC ducts is very likely to destroy them, exposing building occupants to still higher level of both the original contaminants in the duct system and also fiberglass particles.
  
  Similarly, thin plastic-lined flex-duct may be destroyed by mechanical duct cleaning methods.
  
  There are also processes using a spray-sealant on HVAC duct interiors as an effort to seal and salvage contaminated fiberglass-constructed or fiberglass-lined ductwork.
  
  That process may be suitable for some situations but I would be worried about leaving a large mold reservoir inside of a duct sytstem that cannot be easily and frequently inspected after such treatment.
  
  Metal HVAC ducts can usually be cleaned successfull.
  
  Also see at MOLD GROWTH on SURFACES, TABLE OF

We have sometimes found that thick absorbent furnishings such as carpets, upholstered couches and chairs, and mattresses that suffer prolonged exposure to a moldy environment may be smelly from MVOCs even if there was no observable actual mold spore or mold growth contamination on those items.

I'd like to know more about the clothes washer you had trouble with and what authoritative references you have on that matter.

At MOLD & ENVIRONMENTAL INSPECTORS we list some inspectors/testers specializing in mold and indoor contaminants. But there may be other well qualified people in your area. Talk with anyone you are considering hiring.

Don't tell them the "right answer" (besides they are likely to have other good ideas). But name your concerns and ask how they will approach the job - stay away from superficial experts who dash in, collect a mold sample, charge you, and leave.

InspectAPedia.com has no financial nor business relationship with products or services discussed at our website.

Below: another example of white mold found in HVAC air ducts, on the duct fiberglass insulation.

On 2019-07-13 by (mod) - White stuff on fiberglass HVAC air duct liner - is this drywall dust, effloresence, or mold?

Morgan:

The white material on the fiberglass duct liner in your photo looks like mold to me by its growth pattern and supported by your case history.

White deposits, if they were alone with nbo other colors of apparent mold colonies, might also be suspected to be drywall dust from sanding dust that was sent through the duct system. Some further visual inspection (and photos) would allow a more-confident opinoin.

Drywall dust? if the material were white drywall dust you'd find it first and thickest at the air inlet or air return duct and on the blower fan blades in the air handler.

Absent heavy white goop deposits in those locations and then finding such white deposits only downstream from those locations is a compelling argument against dyrwall dust even without further testing.

Effloresence? The white material will not be effloresence. Effloresence is a mineral salt left behind when water passes through and then evaporates from the surface of masonry materials like concrete, concrete block, brick, mortar, stone.

Details are at EFFLORESCENCE SALTS & WHITE DEPOSITS

More photos of mold on or in HVAC ducts are

at MOLD on DUCT SUPPLY or RETURN REGISTERS

Also see AIRBORNE PARTICLE & MOLD LEVELS in DUCTWORK.

On 2019-07-13 by Morgan - white deposits in ductwork

Hi - reading a lot on this website as we are renters in a 3-level (w/ HVAC unit in 4th level crawl space) townhome in NC. I independently hired an air duct cleaning service, since I noticed that we were still wiping dust off of surfaces following some drywall repair and I have bad allergies.

The cleaning never started though, since the guy went up to the unit, looked inside the plenum box and suspects there is mold/other growth that needs to be remediate before cleaning can be done.

Couple of things/prior events to keep in mind:

Approx 6 months ago: HVAC utility drain clogged and was running over for a few weeks. We only picked it up due to a leak down on the 1st floor that was coming through drywall.

Approx 3 months ago: ServPro brought in to remove damaged drywall and bring in dryer fans. Drywall was replaced and sanded and painted (hence the dust mentioned above).

Approx 1 month ago: noticed another leak on 1st floor. This one resulted in replacement of HVAC system (coils were dirty, lines freezing over thus causing leak).

This week: duct cleaning service came out but could not proceed further. HVAC company that installed new unit came out and looked at plenum box, saying it is probably efflorescence growing in the fiberglass box due to sediment from the water that runs through the unit. Unit is on 4th floor, in an unconditioned crawl space so during summer months it is hot and humid up there.

I welcome your thoughts on situation and whether you’d recommend a test for mold. Property manager is slow to act, and given I have allergies (esp to mold), I don’t want to just sit around and wait. Photos also attached.

Thanks!

This Q&A were posted originally

at MOLD APPEARANCE on VARIOUS SURFACES

Variation in Airborne Particle Levels in Heating and Air Conditioning Ducts

How much variation in airborne mold or dust level do we see inside heating and air conditioning ducts and air handlers?

The airborne particle sample trace photograph above, prepared by the author, shows a one liter airborne particle trace collected inside of a heating furnace return air plenum using a Burkard Personal Air Sampler.

Our second airborne particle level photograph (below) shows a second particle trace collected in the same location, with the same volume of air, with one difference: we tapped lightly on the side of the air plenum during the sampling process.

Even before counting the number airborne particles of any type per liter of air it is obvious that even modestly aggressive sampling (rapping on the plenum to stir up local dust) can make a large difference in the level of particles seen in the sample result.

We conducted this test during a post mold remediation clearance inspection of a previously mold-contaminated air conditioning system.

The remediation contractor vehemently disagreed with the procedure of tapping on the ductwork during testing, informing us that "... his hygienist never did such a thing".

We agree that consistency in test methods is important in order to be able to compare one mold test with another.

However if we're looking for the presence or absence of a significant mold or allergenic dust reservoir that should have been removed, a little aggressiveness in sampling can be useful and in fact more accurate as well.

In sum, do not rely on the accuracy of airborne particle counts alone: Since air samples do not capture a representative picture of the indoor environment an indoor air quality investigator should not rely simply on conventional airborne particle quantitative analysis (particle counts per cubic meter).

Readers concerned with mold contamination in heating and air conditioning air handlers and ductwork should

see BLOWER LEAKS, RUST & MOLD

and AIRBORNE PARTICLE & MOLD LEVELS in DUCTWORK where we describe how to test HVAC systems and ductwork for mold.

Mold in HVAC ductwork is also discussed

at WHY DOES MOLD GROW in INSULATION?.

See SLAB DUCTWORK for the role of in-slab placement of air ducts in the formation of mold contamination in HVAC systems.

These critical mold testing accuracy questions are discussed in this paper.

Readers should also

see MOLD LEVEL IN AIR, VALIDITY,

and for a more in-depth critique of popular mold testing methods than this tutorial

see MOLD TESTING METHOD VALIDITY or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Mold on Fiberglass HVAC Duct Interior Surfaces: Tape Sampling

While it is normal to find incidental levels of mold spores, pollen grains, insect fragments, mite fecals, and of course higher levels of fabric fibers and skin cells on the interior of HVAC ductwork, where the duct interior has been wet or has been exposed to high levels of airborne building mold, we may find actual mold growth on the duct interior surface.

Here we show a normally-soiled fiberglass lined HVAC duct, except for those white areas that made the home owner raise a question of the presence of mold contamination.

We were not sure if these white spots in the ductwork were mold or something else until we examined tape samples of the duct surface in our InspectApedia.com lab.

Take a closer look at this photo and you'll see clear adhesive tape (outlined in yellow) applied to the duct interior surface to collect a sample of this white stuff for lab analysis.

[Click to enlarge any image]

I took care to place the tape over what I thought was a representative area of the duct liner where it would collect both the dark debris and the white particles that I suspected might be mold.

You can see that had the tape been placed in the area shown in the left of the photo the sample would not have collected these white particles and it might have missed identifying them.

Our study found Cladosporium sp., Aspergillus sp. and Penicillium sp. in heavy growth in the ductwork.

Details of this air duct mold contamination study based on clear adhesive tape samples of the mold-suspect surface of the air duct are found

at FIBERGLASS AIR DUCT MOLD TEST.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-09-24 - by (mod) -

Alan

I can't make a sound assessment of just what's needed from a brief text; you need an onsite expert;

But most-likely you're going to need to

- find the leak or moisture source that's causing mold growth and fix that

- find and remove any insulation that has been wet or is mold-contaminated

- fix the ductwork

- re-insulate

All of those are normal contractor tasks.

On 2020-09-24 by alan

Hi I had blown insulation put in over duct work that apparently has disconnections and holes. I now have a strong moldy smell, even when system is off. Also a strong moldy smell from the unit itself. It is an old unit and vents have rusted out, some to holes where duct work is connected. How can the duct work be replaced now that it is entombed in blown in insulation?

On 2019-10-12 - by (mod) -

I agree Carlos that maintenance is essential to keep from having leaks or moisture problems that in turn contribute to indoor mold problems.

However that's not something we at InspectApedia.com can offer.

InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information for the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website.

On 2019-10-12 by Carlos Fanning

One needs to provide preventive maintenance service.

On 2019-06-15 - by (mod) -

It doesn't look as if the leaks is "fixed" to me but of course one can't inspect the building by just a brief texting into photo.

One of the concerns of said if the ceiling is gypsum board or drywall got wet and was not removed there's probably a mold problem. Insulation above could be damaged or moldy from leaks as well.

On 2019-06-15 by Cora Doreen Lopez

last summer the a/ c wasn't cooling.. They refilled w refrigerant ..not sure if They located and repaired the leak....well.

3 mos ago..during a storm.. Water leaked through the vent in ceiling..rusty and quite

A lot of water.. The landlord said" it was fixed.. Bur..the ceiling has a yellowish coat.and there is growth on ceiling..new patches have spread out..I was wondering If he took the right steps..as of now..he thinks I'm over reacting... he said: "on roof.

.they opened the duct, cleaned it..sealed duct on roof,patched a piece of roofing. A/c gut tested it..said it was dirt..no mold in the a c return...coils were good...the leak never hit the insulation...it was inside the duct.. Water leaked from within..( during a storm) Im uploading a pic of kitchen ceiling

On 2018-11-17 by (mod) - reader likes organic mold spray

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: surface spray or treatment is not an adequate remedy for mold contamination in buildings; you need to remove the mold, including hidden in building cavities, and fix its cause.

Watch out: Just spraying a "moldy" 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.

...

Continue reading at AIRBORNE PARTICLE SIZE DEFINITIONS & TYPES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see AIRBORNE PARTICLE & MOLD LEVELS in DUCTWORK FAQs - questions and answers posted originally on this page

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
• DUCT DAMAGE, MECHANICAL
• FIBERGLASS AIR DUCT MOLD TEST
• FIBERGLASS INSULATION MOLD - home
• MOLD on DUCT SUPPLY or RETURN REGISTERS - more photo examples of mold in ductwork
• 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
• 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 at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to BUILDING ENVIRONMENT

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