DUCT CLEANING ADVICE - CONTENTS: can moldy air ducts be cleaned? Yes and no - it depends on the type of ductwork. Should HVAC ducts contaminated with asbestos, mold, or other contaminants be cleaned at all? Sometimes. HVAC duct cleaning advice.
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Advice for cleaning contaminated HVAC ducts:
This article gives advice on the cleaning of mold-contaminated air ducts in buildings. Some types of ductwork can and should be cleaned while other types of HVAC duct cannot be effectively cleaned and are at risk of being destroyed by aggressive cleaning efforts. If those ducts are badly contaminated they should be replaced.
This article series explains the cause, detection, and hazards of mold growth in fiberglass insulation in residential
and light-commercial building and gives advice about dealing with moldy building insulation or ductwork. Mold may grow at extensive or problematic levels in some building insulation materials used in walls, floors, ceilings as well as in HVAC air duct systems.
Advice for Suspected or Known Mold-Contamination in HVAC Ductwork (Air ducts, heating ducts, air conditioning ducts)
Here is a photograph of white or light gray mold growth on the interior surface of a fiberglass-lined air duct.
[Click to enlarge any image]
While more investigation was required, we speculated that the Atlanta Georgia home where this duct mold was found had either suffered water or high moisture in the ductwork or there had been another source of high levels of Aspergillus, Penicillium, and perhaps other molds in the building's indoor air.
High exposure levels, or repeated exposure to high levels of this type of airborne mold can cause serious illness such as Aspergillosis.
See ASPERGILLOSIS for details.
Should You Clean Flooded, Contaminated, or Moldy Air Ducts?
If visual inspection, possibly supported by testing (not usually required) confirms that the interior of an air conditioning or heating duct system is badly soiled or contaminated with high levels or large areas of asbestos, mold, rodent feces or urine, insect fragments such as cockroach parts, or other allergens or pathogens then the movement of building air through the duct system is likely to distribute those particles into air breathed by building occupants.
The actual hazard level of such ductwork can be difficult to determine. Air testing in the building or in the ductwork might confirm high levels of hazardous particles but if it doesn't that is not an assurance that the ductwork is safe, since the level of airborne particles varies enormously depending on when and how a test is performed and on variations in building conditions.
If HVAC ducts have been flooded (photo below) or exposed to sewage leaks they should be cleaned and sanitized, or replaced completely if the ductwork is a type that cannot be cleaned. at WATER & ICE IN DUCT WORK you will find more advice for cleaning ductwork subjected to flooding
Only Metal Ductwork May be Able to Be Cleaned
Metal HVAC ducts like the ductwork shown above, whose insulation is on the duct exterior and that present a simple metal surface on the duct interior can usually be successfully cleaned by a duct cleaning professional.
Fiberglass Lined HVAC Ducts & Flex-Duct Cannot be Safely Cleaned by Mechanical Means
Watch out: Fiberglass lined ductwork may be seriously damaged by mechanical cleaning, increasing the subsequent release of irritating airborne fiberglass particles into building air and actually reducing the resistance of such ductwork to future debris and moisture and even mold accumulation. Both of the photos above show mechanically-damaged fiberglass on the inside of air ducts. More about mechanically-damaged HVAC air ducts is at DUCT DAMAGE, MECHANICAL.
Other badly contaminated ductwork such as flex-duct, moldy fiberglass-lined or fiberglass-panel ductwork should be replaced. And in any case you should address the cause of mold growth and correct that as well or the problem will simply repeat itself.
HVAC Duct Cleaning Advice from the US EPA - supplemented by additional expert opinion
If you think the heating or air conditioning (HVAC) system may be contaminated with
mold, read the EPA's guide SHOULD YOU HAVE the AIR DUCTS in YOUR HOME CLEANED? [PDF] before taking further action. Retrieved 2016/11/12, original source: www.epa.gov/iaq/pubs/airduct.html, or call the US EPA at (800) 438-
4318 for a free copy.
Turn off Air Conditioning or Heating Systems That are Mold-Contaminated
The U.S. Environmental Protection Agency recommends that you do not run contaminated air conditioning or heating systems (that use forced air and air ducts).
Watch out: in addition to the EPA advice given here, you should not run HVAC systems in buildings known to be contaminated with anything that is likely to be airborne, as doing so virtually assures that the interior of the HVAC system is going to become also contaminated if it wasn't already in that condition.
Here is the US EPA advice - excerpted:
“Do not run the HVAC system if you know or
suspect that it is contaminated with mold - it could spread mold throughout the building”. 
Buildings in areas where high humidity and high use of air conditioning such as Florida and Louisiana in the U.S. experience very high levels of condensate produced by the air conditioning system, so high that condensate sometimes blows into the ductwork itself rather than all draining successfully into the condensate drain system. According to the Florida Department of Health:
Unfortunately, it is thought that most, if not all, heating and air conditioning systems in
Florida will support mold growth at some point. Stopping the use of an air conditioning
system due to suspected mold growth would make most Florida buildings very
uncomfortable during hot and humid weather.
Should you turn off an air conditioner if a
mold problem in the system is found? Ideally, yes. The system should be shut down
while cleaning or mold removal is performed. If the water and/or mold damage was
caused by sewage or other contaminated water, then call a professional who has
experience cleaning and fixing buildings damaged by contaminated water.
Watch out: the U.S. EPA and other sources recommend: [among other details found in the articles listed in our REFERENCES] that
Have your air ducts cleaned if they are
visibly contaminated with substantial mold
growth, pests or vermin, or are clogged with
substantial deposits of dust or debris.
EPA Advice on Using Biocides, Sanitizers & Ozone to Treat Contaminated HVAC Ducts
Watch out: we do not recommend relying on ozone treatments to "clean" or "disinfect" HVAC ducts, and there is question about the effectiveness of both ozone and sanitizers or chemical biocides used in ductwork. Here are excerpts from the EPA document cited above:
Air duct cleaning service providers may tell
you that they need to apply a chemical
biocide to the inside of your ducts to kill
bacteria (germs), and fungi (mold) and prevent
future biological growth. Some duct
cleaning service providers may propose to
introduce ozone to kill biological contaminants.
Ozone is a highly reactive gas that is
regulated in the outside air as a lung irritant.
However, there remains considerable controversy
over the necessity and wisdom of
introducing chemical biocides or ozone into
the duct work.
Among the possible problems with biocide
and ozone application in air ducts:
Little research has been conducted to
demonstrate the effectiveness of most
biocides and ozone when used inside
ducts. Simply spraying or otherwise
introducing these materials into the
operating duct system may cause
much of the material to be transported
through the system and released into
other areas of your home.
Some people may react negatively to
the biocide or ozone, causing adverse
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
any lawsuits or class action over HVAC insulating duct boards?
(Aug 26, 2014) Maggie said:
Are there any type of lawsuits for duct boards?
Insurance won't pay anything for the remediation of my home and I am at a loss on where to even start - no one seems to be able to tell me the source of my leak or what has caused the contamination or how long I've had the mold growth and I am now being told my whole house needs to be remediated because it's blown throughout the duct work for who knows how long and the levels are off the charts
I'm doubtful that lawsuits are the best place to start attacking the problem you describe. I'd start by hiring either an experienced building inspector or HVAC system technician to diagnose the problem you face, including its cause, providing evidence and documentation, not just "opinion" lest you get nowhere. If necessary you may need an independent insurance adjuster to help out.
From just your note we don't know what contamination is the concern, nor how we know what's been blown through the building, at what levels, and causing what need for further cleaning.
(Aug 26, 2014) Anonymous said:
Thanks Dan. I have actually had all the mold testing along with air samples done and that's how I know it's all throughout my house. I have the type of mold and the counts etc. The insurance adjuster is coming to see if there's any possibility of them paying for any of it - but they say there's slim to no chance of them paying for any of it and if they do it is a minimal amount of the cleanup.
I am in the process of getting estimates from 3 mold remediation companies and an estimate from a HVAC company for replacement of the duct board and/or whole system. I spoke to a real estate agent about "resale" values and the effect of mold in the home and he is actually the one who suggested researching if there were any lawsuits relating to duct boards since insurance doesn't pay for anything etc. I did a google search but came up with nothing. The cost is very prohibitive to wanting to get your house clean so it's all pretty discouraging.
If your HO policy excludes mold damage you're not covered.
WATCH OUT: DO NOT allow a superficial inexpert "cleanup" if in fact there is a large area of mold contamination - inexpert work may further spread contamination and require still more professional and costly cleanup. Before proceeding with cleanup you need a reliable mold remediation plan defining the scope of work, containment, etc.
(Aug 27, 2014) Maggie said:
Yes the insurance company came out today to do their inspection and nothing is covered. I have 4 companies coming tomorrow to provide me with quotes. Two of them work with insurance companies all the time and are supposed to be two of the top mold removal companies (Rainbow Intl and ServPro) the other is Advanta and the 4th is AAS Restoration. If you've heard of any of these companies and have any reviews or thoughts on them I would appreciate any feedback. I've read Angies list reviews and other online reviews and really haven't seen too many bad reviews on any of them.
I also had a duct cleaning service come in that was NADCA certified and they were telling me about some type of service that they spray and paint and the manufacturer of the product guarantees no new regrowth or old leaks of mold for 10 years. I'm guessing this would be the cheapest but not sure if it is the most effective. If you have an opinion on that too I would appreciate your input. ServPro also told me they use a different testing company because the mold inspection company I used tends to be very "over the top" with their recommendations. For instance because my readings on the 3rd floor were high they suggested having the whole house HEPA vaccumed. ServPro suggested the whole house may not require "total cleaning"
He stated some companies will then try to tell you you have to have absolutely everything cleaned or thrown away - like sheets, clothes and if you have a stuffed animal it would be thrown away. Tables could be cleaned but some furniture couldn't - so sometimes the "over the top" recommendations are not necessary and companies may try to get me to do more than necessary. Not sure if you have thoughts on that either but if I do the minimum cleaning - in other words replace duct work clean extremely high level areas with HEPA vacuuming etc. how much damage will I leave if I don't HEPA clean whole house. I of course realize these are all broad opinions on items that you are not seeing or reports you are reading. Thank.
Reply: "throw everything away" is usually inappropriate advice
I agree with your ServPro rep that "throw everything away" is usually inappropriate advice. Some items such as hard surface items are usually easily cleaned; some soft goods can be laundered or drycleaned. Other items such as water damaged carpets, padding, drywall, upholstered couches are tossed out.
Ask a Question or Search InspectApedia
Questions & answers or comments about Mold in Air Ducts: cause, detection, cure, & prevention of moldy HVAC ductwork.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
"Indoor Mold and Health,
A Fungus AmonG Us", Florida State Department of Health, Florida Department of Health
Division of Environmental Health
Bureau of Community Environmental Health
Radon and Indoor Toxics
4052 Bald Cypress Way, Bin A08
Tallahassee, FL 32311
1-800-543-8279, web search 08/05/2011, original source: http://www.doh.state.fl.us/environment/community/indoor-air/Indoor_Mold_and_Health.pdf. Quoting:
The Florida Department of Health has developed this brochure to address some of the most
common questions and concerns about indoor mold, how it affects human health, and ways in
which you can prevent or remove it.
 Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com 11/06
 Ahearn, D.G., S A Crow, R B Simmons, D L Price, J A Noble, S K Mishra and D L Pierson, "Fungal colonization of fiberglass insulation in the air distribution system of a multi-story office building: VOC production and possible relationship to a sick building syndrome", Journal of Industrial Microbiology & Biotechnology, Volume 16, Number 5 (1996), 280-285, DOI: 10.1007/BF01570035. Abstract:
Complaints characteristic of those for sick building syndrome prompted mycological investigations of a modern multi-story office building on the Gulf coast in the Southeastern United States (Houston-Galveston area). The air handling units and fiberglass duct liner of the heating, ventilating and air conditioning system of the building, without a history of catastrophic or chronic water damage, demonstrated extensive colonization with Penicillium spp and Cladosporium herbarum. Although dense fungal growth was observed on surfaces within the heating-cooling system, most air samples yielded fewer than 200 CFU m–3. Several volatile compounds found in the building air were released also from colonized fiberglass. Removal of colonized insulation from the floor receiving the majority of complaints of mouldy air and continuous operation of the units supplying this floor resulted in a reduction in the number of complaints.
 Ahearn, D.G., S.A. Crow, R.B. Simmons, D.L. Price, S.K. Mishra and D.L. Pierson, "Fungal Colonization of Air Filters and Insulation in a Multi-Story Office Building: Production of Volatile Organics", Current Microbiology Volume 35, Number 5 (1997), 305-308, DOI: 10.1007/s002849900259, Abstract:
Secondary air filters in the air-handling units on four floors of a multi-story office building with a history of fungal colonization of insulation within the air distribution system were examined for the presence of growing fungi and production of volatile organic compounds. Fungal mycelium and conidia of Cladosporium and Penicillium spp. were observed on insulation from all floors and both sides of the air filters from one floor. Lower concentrations of volatile organics were released from air filter medium colonized with fungi as compared with noncolonized filter medium. However, the volatiles from the colonized filter medium included fungal metabolites such as acetone and a carbonyl sulfide-like compound that were not released from noncolonized filter medium. The growth of fungi in air distribution systems may affect the content of volatile organics in indoor air.
 Price,D. L., R. B. Simmons, I. M. Ezeonu, S. A. Crow and D. G. Ahearn, "Colonization of fiberglass insulation used in heating, ventilation and air conditioning systems", Journal of Industrial Microbiology & Biotechnology Volume 13, Number 3 (1994), 154-158, DOI: 10.1007/BF01584000, Abstract: The number of fungal species colonizing thermal and acoustic fiberglass insulations used in heating, ventilation, and air conditioning (HVAC) systems was fewer than that obtained from initial direct culture of these insulations. The colonization, determined by the microscopic observation of conidiophores with conidia, was primarily of acrylic-latex-facing material, but eventually the fungi permeated the fiberglass matrix. Isolates of Aspergillus versicolor were most often obtained from non-challenged insulation, whereasAcremonium obclavatum appeared to be the primary colonizing fungus in high-humidity (>90%) challenge chambers. At a lower humidity (about 70%) Aspergillus flavus was one of the more prominent fungi. Not all duct liner samples were equally susceptible to colonization and duct board appeared relatively resistant to colonization.
 Simmons, R. B. and S. A. Crow, "Fungal colonization of air filters for use in heating, ventilating, and air conditioning (HVAC) systems", Journal of Industrial Microbiology & Biotechnology Volume 14, Number 1 (1995), 41-45, DOI: 10.1007/BF01570065, Abstract:
New and used cellulosic air filters for HVAC systems including those treated with antimicrobials were suspended in vessels with a range of relative humidities (55–99%) and containing non-sterile potting soil which stimulates fungal growth. Most filters yielded fungi prior to suspension in the chambers but only two of 14 nontreated filters demonstrated fungal colonization following use in HVAC systems. Filters treated with antimicrobials, particularly a phosphated amine complex, demonstrated markedly less fungal colonization than nontreated filters. In comparison with nontreated cellulosic filters, fungal colonization of antimicrobial-treated cellulosic filters was selective and delayed.
 Ifeoma M. Ezeonu, Daniel L. Price, Sidney A. Crow and Donald G. Ahearn, "Effects of extracts of fiberglass insulations on the growth of Aspergillus fumigatus and A. versicolor", Mycopathologia Volume 132, Number 2 (1995), 65-69, DOI: 10.1007/BF01103777
Water extracts of thermal and acoustic fiberglass insulations used in the duct work of heating, ventilation and air conditioning (HVAC) systems supported germination of conidia and growth of Aspergillus versicolor (Vuillemin) Tiraboschi 1908–9 and Aspergillus fumigatus Fresenius 1863. Urea, formaldehyde and unidentified organics were detected in the extracts. Formaldehyde in concentrations similar to those found in the extracts restricted the growth of both species in enriched media. A. versicolor, the more common species associated with fiberglass insulations, was more resistant to formaldehyde than A. fumigatus.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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 as /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA
US EPA - Una Breva Guia a Moho - Hongo [on file as /sickhouse/EPA_Moho_Guia_sp.pdf - - en Espanol
Fiberglass in buildings: hazards, testing, cleanup, prevention: references & products
For more information about fiberglass as an indoor air quality concern see:
Asbestos: How to find and recognize asbestos in buildings - visual inspection methods, list of common asbestos-containing materials (Asbestos is not fiberglass and vice versa).
BASEMENT MOLD includes examples of moldy fiberglass insulation found in basements
CRAWLSPACE MOLD includes additional examples of moldy fiberglass insulation found in
LAB IDENTIFICATION OF FIBERGLASS photographs and text assist in laboratory identification of fiberglass fibers and fragments in air, dust, or material samples in the laboratory using forensic microscopic techniques.
Mold in Fiberglass building insulation, when, why, and how fiberglass becomes a reservoir of problem mold in buildings.
Fiberglass carcinogenicity: "Glass Wool Fibers Expert Panel Report, Part B - Recommendation for Listing Status for Glass Wool Fibers and Scientific Justification for the Recommendation", The Report on Carcinogens (RoC) expert panel for glass wool fibers exposures met at the Sheraton Chapel Hill Hotel, Chapel Hill, North Carolina on June 9-10, 2009, to peer review the draft background document on glass wool fibers exposures and make a recommendation for listing status in the 12th Edition of the RoC. The National Institute of Environmental Health Sciences is one of the National Institutes of Health within the U.S. Department of Health and Human Services. The National Toxicology Program is headquartered on the NIEHS campus in Research Triangle Park, NC. The National Institute of Environmental Health Sciences is one of the National Institutes of Health within the U.S. Department of Health and Human Services. The National Toxicology Program is headquartered on the NIEHS campus in Research Triangle Park, NC.
Following a discussion of the body of knowledge, the expert panel reviewed the RoC listing criteria and made its recommendation. The expert panel recommended by a vote of 8 yes/0 no that glass wool fibers, with the exception of special fibers of concern (characterized physically below), should not be classified either as known to be a human carcinogen or reasonably anticipated to be a human carcinogen. The expert panel also recommended by a vote of 7 yes/0 no/1 abstention, based on sufficient evidence of carcinogenicity in well-conducted animal inhalation studies, that special-purpose glass fibers with the physical characteristics as follows longer, thinner, less soluble fibers (for 1 example, > 15 μm length with a kdis of < 100 ng/cm2/h) are reasonably anticipated to be a human carcinogen for the listing status in the RoC. The major considerations discussed that led the panel to its recommendation include the observations of tumors in multiple species of animals (rats and hamsters). Both inhalation and intraperitoneal routes of exposure produced tumors, although inhalation was considered more relevant for humans.
Fiberglass insulation mold: occurrence of mold contamination in fiberglass insulation can be impossible to see with the naked eye, but can be significant
World Health Organization International Agency for Research on Cancer - IARC Monographs on the Evaluation of Carcinogenic Risks to Humans - VOL 81 Man-Made Vitreous Fibers, 2002, IARCPress, Lyon France, pi-ii-cover-isbn.qxd 06/12/02 14:15 Page i - World Health Organization, 1/21/1998. - Fiberglass insulation is an example of what IARC refers to as man made vitreous fiber - inorganic fibers made primarily from glass, rock, minerals, slag, and processed inorganic oxides. This article provides enormous detail about fiberglass and other vitreous fibers, and includes fiberglass exposure data.
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81.pdf - the article (large PDF over 6MB)
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6A.pdf - article details
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6C.pdf - studies of cancer in experimental animals in re vitreous fibers such as fiberglass;
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6E.pdf - summary of data reported & evaluation
http://monographs.iarc.fr/ENG/Monographs/vol81/mono81-6F.pdf for the article references
To search the IARC monographs on various environmental concerns and carcinogens, use http://monographs.iarc.fr/ENG/Monographs/PDFs/index.php
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates 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.
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.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones