How to Assess the Level of Mold Contamination in HVAC Ducts & Air Handlers

How to Test Air Ducts 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?
- What are the sources of variation in the mold level that air tests can detect?
BLOWER LEAKS, RUST & MOLD - separate article explains causes of leaks & mold in HVAC ducts
DIRTY A/C BLOWERS - separate article includes leaks, rodents, & mold in air handler units
PARTICLE & MOLD LEVELS in DUCTWORK
Questions & answers abouthow to measure the level of mold contamination in HVAC air ducts and blower units
References

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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. 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

Readers concerned with mold contamination in heating and air conditioning air handlers and ductwork should see BLOWER LEAKS, RUST & MOLD and 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

Question: After dealing with a moldy washing machine and even a mold remediation we are focusing on our ductwork: 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.

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 KITS for DUST, MOLD, PARTICLE TESTS - 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.
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 Mold Atlas & Particles 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 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. (MOLD TESTING METHOD VALIDITY) .]

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. It should be possible to properly launder sheets and towels to leave them smelling clean and fresh. But if a mattress or bed pad also got smelly from mold volatile organic compounds (MVOCs, that's what you are probably smelling), then laundering the sheets might make them ok at first (until they are placed on the bed) but the smell could still be in the bed due to the mattress or mattress pad. Details are 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

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 left hand photograph shows a one liter airborne particle trace collected inside of a heating furnace return air plenum using a Burkard Personal Air Sampler.

The right hand photograph 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).

Frequently Asked Questions (FAQs) About HVAC Ducts Contaminted by Mold

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

Mold in HVAC flex duct (C) InspectAPedia

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 samples, (see MOLD TEST REASONS ) but 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.

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.
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, A/C and also see WET CORRODED DUCT WORK for some diagnostic help and cleanup advice when moldy ductwork is a problem.

See MOLD EXPERT, WHEN TO HIRE for help in deciding if it's appropriate to bring in an expert.

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Technical Reviewers & References

Related Topics, found near the top of this page suggest articles closely related to this one.

Thanks to Susan Flappan, Flappan Consulting, moldetect.com, Overland Park KS, 913-402-1131, for contributing comments and some suggested text from ACGIH Bioaerosols: Assessment and Remediation 12/2006.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.

Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.

Building inspection education & report writing systems from Carson, Dunlop & Associates Ltd

Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
Environmental Health & Investigation Bibliography - our technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Adkins and Adkins Dictionary of Roman Religion discusses Robigus, the Roman god of crop protection and the legendary progenitor of wheat rust fungus.
Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
US EPA - Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol

Mold Contamination Testing, Cleanup, Prevention: references & products

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems
Aerobiology, Building Science, Microscopy, & Laboratory References, an extensive technical bibliography
Allergens: what they look like in buildings
Associations: Sick House, Sick Building, SBS - Air Quality, Government, Private Associations and Information Resources
Atlas of Clinical Fungi, 2nd Ed., GS deHoog, J Guarro, J Gene, & MJ Figueras, Centraalbureau voor Schimmelcultures, Universitat Rovira I Virgili, 2000, ISBN 90-70351-43-9 (you can buy this book at Amazon) - The Atlas of Clinical Fungi is also available on CD ROM
Atlas of Mold Related Illness: Index of Symptoms and health, physical, neurological, psychological, and other complaint which people suspect may be mold or building-related.
Atlas of Indoor Mold, Online Clinical Mold Atlas, Toxins, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
Black Mold that is Harmless Photos of recognizable, usually harmless black mold on wood, bluestain, ceratocystis, ophistoma
Building Floods: quick steps after a building flood or plumbing leak can prevent costly mold contamination
Classes of Mold: what types of cosmetic, allergenic, or toxic mold are a problem? Can mold be cleaned-up successfully?
Clinical Mold References - Detailed bibliography of mold reference texts
"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm
"Disease Prevention Program for Certain Vegetable Crops," David B. Langston, Jr., Extension Plant Pathologist - Vegetables, University of Georgia (PDF document) original source: www.reeis.usda.gov/web/crisprojectpages/209797.html
"Disease Prevention in Home Vegetable Gardens," Patricia Donald, Department of Plant Microbiology and Pathology, Lewis Jett
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202
"Management of Powdery Mildew, Leveillula taurica, in Greenhouse Peppers," Ministry of Agriculture and Lands, British Columbia - Original source: www.agf.gov.bc.ca/cropprot/peppermildew.htm
Environmental Health & Investigation Bibliography - our own technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.
Fiberglass: Mold in Fiberglass Insulation© 2005 comments about a field study in process, & more about health hazards from fiberglass insulation - DJF
Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.
Fungi, Identifying Filamentous, A Clinical Laboratory Handbook, Guy St-Germain, Richard Summerbell, Star Publishing, 1996, ISBN 0-89863-177-7 (English) (buy at Amazon)
Looking for Mold Procedure: what mold is often found where in buildings - simple technical presentation
Meruliporia: the house eating fungus or "poria"
Mold Action Guide: Step-by-Step Instructions, What to do about mold, mildew, and other indoor allergens
MOLD APPEARANCE - WHAT MOLD LOOKS LIKE Photos of what mold looks like in buildings
MOLD APPEARANCE - STUFF THAT IS NOT MOLD Photos of NOT-mold material that is sometimes mistaken for mold
MOLD ATLAS & PARTICLES INDEX, Pathogens, Allergens and Other Indoor Particles - Medical Health Effects of Mold (separate online document)
MOLD BY MICROSCOPE Mold under the microscope - photo identification of the most common indoor molds found in buildings
Mold FAQs Answers to Most Questions about Indoor Mold, Mold Related Illness, Mold Cleanup, Mold Prevention
US EPA: Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens
Mold Test Kits - How to Collect and Send Your Own Mold Sample to our mold testing lab or to any mold lab you wish
Most Common Indoor Molds Found in Buildings, A Table of
Mycology, Fundamentals of Diagnostic, Fran Fisher, Norma B. Cook, W.B. Saunders Co. 1998, ISBN 0-7216-5006-6 (buy this book at Amazon)
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Rot concerns in buildings-some building mold such as Meruliporia incrassata "Poria" risks serious rot and hidden structural damage
US EPA: Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol

OTHER IAQ ISSUES: How To Find and Address Other Indoor Air or Indoor Environment Contaminants Besides Mold

Mold or allergens may not be the only or even the main indoor environmental contaminant. Don't let media attention to mold cause so much enviro-scare fear that other, possibly more urgent hazards go un-addressed.

Fiberglass building insulation and HVAC duct work insulation hazards
Sewage and Septic backup contamination in buildings: inspection, testing, remediation, & references to expert sources
Other environmental risks: Asbestos, carbon monoxide, electromagnetic fields, environmental illness, fiberglass, MCS - multiple chemical sensitivity, toxic gases, etc
Indoor Gas Sampling Plan for Residential Buildings lists a number of toxic indoor gases which we test for, depending on the building complaint and building conditions
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Pet control - if you can't say goodbye to your bird, cat, dog, guinea pig, hamster, tropical fish, then limit the areas they occupy and limit the airflow from that area to sleeping or other areas of the building, use allergenic bedding, eliminate wall-to-wall carpeting, improve housecleaning including use of a HEPA-rated vacuum cleaner. For more details see our article Dog, Cat, and Other Animal Dander - Information for Asthmatics and Indoor Air Quality
Rodents, Mice, Squirrel Control - I find high levels of mouse and rodent dander, fecal dust, and urine-contaminated dust in some buildings, and high levels of these materials in building insulation in those locations. If you have a mouse problem, particularly if mice and their waste (fecals or urine) are contaminating the building HVAC or building insulation, may need both steps to clean up or remove infected materials and steps to stop an ongoing rodent problem. If squirrels are a problem, the cleanup needs to include closing off entry openings into the building. Get some help from a licensed pest control expert.
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