Very dirty HVAC air duct interior (C) Daniel Friedman HVAC Air Duct Contamination
Causes, Detection, Cleaning, Prevention of bacterial, dirt, insect, mold or other duct contaminants - resource list

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Contamination in air conditioning or heating ducts:

List of HVAC air duct contamination sources & types, diagnostic articles & duct contaminant or odor detection, testing & contaminant removal or prevention advice.

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Contaminants in HVAC Air Ducts

Water and rodents in air duct (C) D FriedmanThis article is the topic index to our article series addressing just about every common source of contamination in heating & cooling duct systems, including bacteria, dust, fiberglass fragments, mold or odors that appear to originate in or be transported by the buildings air duct system.

[Click to enlarge any image]

My photo at page top shows a fiberglass-lined HVAC duct that was tortured and damaged by an attempt at mechanical cleaning. The result of such treatment is likley to include the blowing of irritating, potentially harmful fiberglass fragments into the building indoor air.

The photo shown just above illustrates an in-slab air duct that was not only quite dirty but that had been repeatedly flooded.

My OPINION is that water in air ducts invites growth of more-serious mold, bacterial contamination and possibly other pathogens, particularly if the duct was flooded during an area flood that brought sewage waters into a building.

Below is an alphabetical list of common air duct contaminants and contamination sources or duct test & inspection methods.

Following our list of duct contaminant diagnostic articles we illustrate and discuss some common examples of air duct contamination, dust, dirt and debris - or perhaps of more concern, pathogens.

Watch out: don't panic if you see dust inside the HVAC system, or exposed fiberglass. Both of these conditions are common and do not necessarily mean that the air ducts are unsanitary or unsafe.

However if you see signs of water, visible mold, flooding, rodents, or if you see that the duct interior has been damaged like the fiberglass-lined duct shown a the top of this page (DUCT DAMAGE, MECHANICAL) there may indeed be a problem that needs to be addressed.

Article Series Contents

Photo of tranite cement-asbestos material used for air ducts in a slab over a sewer pipe (C) Daniel Friedman and Conrad Mud in a building air duct after building flooding (C) Daniel Friedman

At above left we show transite HVAC ducts routed in a floor slab immediately over a sewer line. When the sewer line leaked sewage odors were picked up in and transported by the in-slab ductwork.

Details of this case are presented at SLAB DUCTWORK.

At above right we illustrate an air duct that was routed below the first floor of a buildnng and accessible from the basement.

A look inside showed us that there had been of a history of flooding - dirt and mud on the duct bottom - meaning that floodwaters had at one time filled the basement.

Watch out: area flooding may contaminate ductwork with sewage or other pathogens even for above-ground-level HVAC ducts, while a building sewage backup can certainly contaminate ductwork run in floors or in a floor slab.


Water and rodents in air duct (C) D Friedman Very dirty HVAC air duct interior (C) Daniel Friedman

At above left we illustrate an abandoned HVAC duct in a concrete floor slab. It's quite apparent that the area remains wet along with an added risk of contaminants of sewage, pesticides, rodents, insects, or anything that spilled on the floor in this area.

Our HVAC duct interior photograph at above right shows a melange of contamination by animal hair, dog food, and rodent droppings. Mice were eating the dog food that spilled into this return air duct opening at a floor register. The potential pathogens invovled here include at least bacteria, possibly hantavirus and mold.

Research & Resources on Contaminated HVAC Ducts / Heating or Air Conditioning Ductwork


Continue reading at AIR LEAKS in RETURN DUCTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see BLOWER LEAKS, RUST & MOLD explains causes of leaks & mold in HVAC ducts

Or see DIRTY A/C BLOWERS includes leaks, rodents, & mold in air handler units





Or see WHY DOES MOLD GROW in INSULATION? that includes photos and test results examining suspected mold on the surface of fiberglass-lined HVAC ductwork.

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DUCTWORK CONTAMINATION at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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