Photograph of fiberglass HVAC duct materialsFiberglass HVAC Duct Hazards

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

HVAC duct damage as a source of airborne fiberglass fragments:

This document provides information about fiberglass hazards in heating and air conditioning ductwork in residential and light-commercial buildings.

We discuss how Fiberglass from HVAC Ducts Can Appear in Indoor Air. Sources and detection of airborne fiberglass in buildings and possible air quality or health issues with fiberglass ducts and other HVAC components.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Recognizing Fiberglass Duct Insulation

Photo of


Fiberglass insulation material appears in several forms in heating and air conditioning systems in both ducts and air handlers themselves.

The most common uses of fiberglass insulating material in HVAC systems includes the cases listed below.

The annotated duct system photographs below show the most common types of fiberglass HVAC duct materials.

We provide these © protected photographs of fiberglass insulated ducts and HVAC components to aid in recognition of these materials.



Flex Duct using fiberglass insulation

Photo of  crimped HVAC duct (C) Daniel Friedman Photo of excessive bend in HVAC duct (C) Daniel Friedman

Flex duct with fiberglass insulation sandwiched between a plastic inner and outer wrap. Flex duct may be used for both supply air (shown here at left, poorly installed and crimped) and return air (second photo) in buildings.

Photo of snaky fiberglass covered flex duct (C) Daniel Friedman Photo of multiple flex duct HVAC lines off of a main trunk (C) Daniel Friedman

The flex duct shown at left is a newly-installed foil-faced flex duct product. The photograph at right shows foil-faced smaller-diameter high-velocity HVAC ducts as well as the main trunk line which has also been covered with foil-faced fiberglass insulation.

Photo of  Photo of normal gray dirt and debris inside of flex duct (C) Daniel Friedman

The flex duct in these photos shows at left, a clean, newly installed duct line, and at right, the typical debris we observe inside of most duct systems. This debris could have been prevented inside the duct system by better filtration at return air inlets. In a home without mold or allergen or similar indoor air quality complaints, usually we find in the lab that this gray dusty debris is comprised principally of skin cells and fabric fibers.

Photo of paint spray inside of hvac flex duct (C) Daniel Friedman

This photo shows white paint over sprayed into a ceiling supply duct - not to be mistaken for duct contamination, but an indicator of hasty workmanship.

Photo of Goodman gray flex duct deterioration (C) Daniel Friedman Photo of deteriorated fiberglass insulated gray covered Owens Corning gray flex duct (C) Daniel Friedman

Goodman™ gray flex duct has failed in the first photo above. Owens Corning ValuFlex™ gray flex duct can also show this failure as shown in the second photo where, like the Goodman flex duct, the plastic exterior duct wrap has failed [second photo by Mark Cramer, Tampa Florida].

Rigid rectangular fiberglass duct work

Photo of  retangular fiberglass ductwork (C) Daniel Friedman Photo of foil covered fiberglass insulation inside an HVAC air handler (C) Daniel Friedman

Rigid rectangular fiberglass duct work is visible as the return air plenum in the right of the first photo above. This material is usually used for HVAC trunk lines and a variant of it is often found inside of air handlers (right hand photo).

Fiberglass insulating mats and duct linings

Photo of dirty exposed fiberglass duct liner (C) Daniel Friedman Photo of

Fiberglass insulating mats and duct linings are used inside air handlers and on the interior of metal HVAC ducts both inside buildings and in exterior roof-mounted duct systems.

Fiberglass insulating wrap

Photo of  Photo of

Fiberglass insulating wrap installed on the outside of metal duct work or air handling equipment is shown in the left photo above.

Building insulation is not designed for use inside of HVAC ducts and lacks the binding resin that is applied to minimize airborne fiberglass particle release into the building. The above-right photo shows home-made air handler and return plenum insulation liner using fiberglass batts, resulting in a higher risk of release of unusual levels of fiberglass into the indoor air of the building.

More examples of damage to ductwork due to physical events or mechanical activity or cleaning are found

Round rigid fiberglass HVAC ducts

Photo of  Photo of cross section of rigid round fiberglass HVAC ductwork with exposed fiberglass interior surface in the air path (C) Daniel Friedman

Rigid round fiberglass duct work is sometimes used for distribution of heated or cooled air through building walls or ceilings. Notice that the fiberglass is fully exposed on the interior of this product, making it impossible to clean and providing a surface which easily traps debris.

Fiberglass insulating mats

Photo of  Photo of

Fiberglass insulating mats inside of furnaces and boilers, usually enclosed within a steel jacket surrounding the system but possibly also present within the air handler of furnaces and central air conditioning blowers.

The insulation shown in these photos has been subject to condensate or external leaks, risking a mold contamination problem in the system. In the second or right hand photo fiberglass materials have been used inside the air handler sides and top in a foil-faced form (unlikely to release many fibers into the duct system) and a binder-coated mat on the air handler bottom.


Continue reading at FIBERGLASS DUCT, RIGID CONSTRUCTION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see these fiberglass duct articles

Or see these articles about fiberglass hazards in buildings

Or see DISINFECTANTS & SANITIZERS, SOURCES if you need to sanitize or seal air duct interiors


Suggested citation for this web page

FIBERGLASS HVAC DUCTS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Questions & answers or comments about possible sources of small fiberglass fragments found in indoor air & dust samples.

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.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman