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• How to recognize fiberglass heating and cooling ducts and air handler insulation materials
• Sources and detection of airborne fiberglass in buildings
• Possible air quality or health issues with fiberglass ducts and other HVAC components

This document provides information about fiberglass hazards in heating and air conditioning ductwork in residential and light-commercial buildings. © Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Recognizing Fiberglass Duct Insulation

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 (C)-protected photographs of fiberglass insulated ducts and HVAC components to aid in recognition of these materials.

Flex Duct using fiberglass insulation

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.

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.

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.

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.

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

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

Fiberglass insulating wrap

Round rigid fiberglass HVAC ducts

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

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.

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Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

FIBERGLASS HAZARDS
  Recognizing Fiberglass Insulation
  Recognizing Fiberglass Duct Insulation
  Lab Identification of Fiberglass
  Fiberglass Fragment Hazards
  Fiberglass Detection in Building Air
  Mold in Fiberglass Insulation
  Mold in Foam Insulation
  Moldy insulation may look clean
  Why does mold grow in fiberglass?
  When to test insulation for mold
  How to Test for Mold in Insulation
  Fiberglass Hazard References

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More Information on Building Diagnostic Inspections and Repairs

• Fiberglass in Indoor Air, HVAC ducts, and Building Insulation, Indoor Air Quality Investigations: (this article)
• Mold in Fiberglass, when, why, and how fiberglass becomes a reservoir of problem mold in buildings.
• 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.
• Duct System Defects
• Asbestos: How to find and recognize asbestos in buildings - visual inspection methods, list of common asbestos-containing materials

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