Mold & Debris Contamination in HVAC Ducts & Air Handlers

Causes of Ductwork Mold Contamination

While it's normal for HVAC ductwork interior surfaces to collect a layer of building dust, in a healthy building that dust is composed primarily of fabric fibers, skin cells, and perhaps other harmless debris.

However, if there is a mold reservoir anywhere in the building, visible or hidden, it's likely that mold spores will be carried into the HVAC system air handler and ductwork.

Inside both of those components, particularly if there is also a moisture source such as condensation or high building humidity levels, many species of mold will adhere and grow into a new mold reservoir in the equipment, feeding on the organic matter in the duct dust such as skin cells.

Common causes of duct mold contamination then include

1. High levels of moisture in the ductwork - condensate leaks or other water sources
2. A mold reservoir elsewhere in the building
3. Incomplete or missing ductwork insulation - contributing to duct condensation

Other contributors to ductwork mold contamination

• Duct cleanliness. Strong electrostatic effects cause normal deposition of building dust on duct and air handler surfaces. Thicker accumulations of this dust, when combined with moisture, contribute to fungal growth.
• Climate - temperature and humidity ranges that affect the building and its HVAC system.
• Building temperatures
• Building humidity level
• History of leaks into the building or inside it that might have caused a mold reservoir elsewhere in the building over its life
• MIssing insulation on the air ducts themselves.
• Ductwork materials:
  
  While it's indeed possible for mold to grow on the interior surfaces of both metal and plastic ductwork (thanks to the combination of moisture or condensate and organic material such as skin cells that are normal in house dust that will be found inside air ducts),
• Building construction methods & materials that contribute to mold growth (wood frame, masonry, one-family, multi-story, etc).

Watch out: : mold "tests" for duct or air handler mold or other building mold are singularly unreliable as a building screen for mold: a thorough and expert inspection is what's called fo

Watch out: simply cleaning mold contaminagted ductwork is likely to be inadequate.

If the ductwork is moldy there will probably be mold contamination inside the air handler unit, in the supply and return air plenums, and on the blower fan assembly. Those components also need to be attended.

Bottom line: find the mold, remove it, and fix the cause of mold growth

How to Test Air Ducts for Mold Contamination

What is the best way to test for mold in the heating/AC system

Our reader asked:

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.

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

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 AIR HANDLER 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.

White deposits in ductwork might be Mold Contamination?

Our reader asked:

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 monthsago: 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! On 2019-07-13 by Morgan -

This Q&A were posted originally at MOLD APPEARANCE on VARIOUS SURFACES

Discussion 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 DUCTWORK MOLD CONTAMINATION.

Tests for Mold in Ductwork-Limitations

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 AIR HANDLER BLOWER LEAKS, RUST & MOLD

and DUCTWORK MOLD CONTAMINATION- war 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.

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.