Photograph of  asbestos paper wrap on heating/cooling duct exteriorAsbestos HVAC Ducts & Furnaces
A Guide to Identification of Asbestos Materials On or In Heating and Cooling Duct Work or Air Handlers

  • ASBESTOS DUCTS, HVAC - CONTENTS: How to recognize asbestos on or in heating or cooling air ducts or air handlers - a photo guide to recognizing asbestos on HVAC systems such as air ducts, vibration dampers, and heating system in-slab transite ducts or heating system transite chimneys - Photos of asbestos in HVAC ductwork and air handlers, blower units, furnaces, air conditioners
  • POST a QUESTION or READ FAQs about asbestos materials on or inside of heating or air conditioning air ducts or air handlers & blower units

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Asbestos in or on HVAC ducts (air ducts or heating and cooling ductwork) or inside the air handler (blower unit) itself is a possible hazard for which we provide information, photos, & links to additional documents.

This article shows how to recognize asbestos materials in heating and air conditioning ducts, vibration dampers, chimneys, and flues, and air handlers or blower compartments, and it identifies potential asbestos fiber release or carbon monoxide hazards in buildings where certain asbestos and cement-asbestos transite pipe materials are used for ducts or for heating appliance chimneys and vents.

This is part of our article series that describes the inspection of residential air conditioning systems (A/C systems) to inform home buyers, owners, and home inspectors of common cooling system defects.

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Asbestos Materials on or in the Air Conditioning or Heating System Duct Work

This article describes the inspection of heating and air conditioning ducts for visual evidence of asbestos materials in or on HVAC ducts. We also warn about signs of amateur asbestos removal which may merit additional testing and cleanup work.

The photograph at below left shows asbestos paper heating duct wrap. Asbestos in these locations is a possible hazard which may require special attention, particularly if the paper has been damaged as we show here.

Photograph of asbestos paper duct seal Photograph of asbestos fabric on an air conditioning and heating blower vibration damper

At above right is a photo of a coated (note the silver color) asbestos-fabric air handler vibration damper. This fabric is right in the air pathway and should probably be removed.

Article Contents

Also see ASBESTOS PAPER INSULATION on DUCTS and see VIBRATION DAMPENERS for more discussion of this possible asbestos source.

If readers return to the first chapter or view the A/C chapter index, the major components of an air conditioning system are described, sketches and photographs are provided, and common defects for each component are listed along with visual or other clues that may suggest a problem or probable failure of A/C components.

Asbestos - Ductwork Types & Materials

Photograph of asbestos paper duct seal

Another example of asbestos duct wrap is shown in this photograph. During an inspection of the heating or air conditioning duct system and air handler, look for what may be asbestos containing insulating material on the heating system.

  • Cement asbestos "millboard" used as a partial heat shield on wall/ceiling surfaces.

  • Cement asbestos transite pipe used as HVAC air ducts, often set in slabs but also run through building areas; note that this material may also have been used as a chimney or chimney flue.

  • White corrugated insulating material on and hanging from pipes, white paste material surrounding certain plumbing joints.

  • White "paper" wrapped on outside of some heating ducts.

  • White woven material used as flexible joint between some heating ducts.

  • White woven material used as flexible joint in the vibration damper between air handler the duct work.

TRANSITE and SONNO-DUCT Air Conditioning or Heating Duct Material Warnings: asbestos fiber release and carbon monoxide hazards

Photograph of  asbestos paper wrap on heating/cooling duct exterior Photograph of  asbestos paper wrap on heating/cooling duct exterior

While the transite pipe shown here was in use as an exhaust flue (what is the fire rating and fire clearance required?), this material was also used in some buildings for in-slab duct work (SLAB DUCTWORK) .

Caution: Down flow furnace in building with concrete slab and with perimeter duct work raises questions: what is the duct work made of ? Is asbestos material found right in the air pathway in a building? If so there are higher risks of airborne asbestos contamination in that building than otherwise.

Transite chimney Carbon Monoxide Hazards: where used for chimneys in buildings, transite pipe may form a very serious, potentially fatal carbon monoxide hazard due to chimney blockage. We explain how and why the carbon monoxide poisoning hazard develops in our article at Transite Pipes, Chimneys & Flues.

Transite Duct Asbestos Hazards: if used for air ducts transite pipe may be a an asbestos hazard, particularly where the ducts become softened by water exposure (such as air ducts located in floor slabs), potentially releasing asbestos fibers into the building air. See TRANSITE PIPE AIR DUCTS for details.

Sonno Duct (spun composition material) may have absorbed water, collapsed, and be blocking the duct line and potentially inviting a termite infestation or a mold contamination problem in the building.

More identification photographs of transite pipe in buildings can be found at Asbestos Transite Chimneys & Flues and at TRANSITE PIPE AIR DUCTS

ASBESTOS RISKS - on Heating and Cooling Ducts

Photograph of  asbestos paper wrap on heating/cooling duct exteriorWhile there may be no conclusive data nor studies which evaluate hazards regarding presence of this material in residential buildings, it is generally considered by the scientific community to be a potential health risk.

Asbestos heating system insulation is also a potential economic risk as future buyers may be concerned about this material. Disposal costs for this material are increasing.

Depending on condition and location of asbestos material, treatment ranges from doing nothing to complete removal. Removal could involve significant costs.

You should obtain proper technical information and health and safety guidelines before attempting to do anything with this material. It is the breathing of fibers when this material is disturbed, not it's mere presence, which is considered a health risk. When the material is not found in living areas in poor condition treatment is not usually an emergency and you have ample time to become informed, obtain estimates, and select a course of action.

[Offline text files of additional advice for insertion into home inspection reports where asbestos material is observed:
... HEAT.036 - Asbestos - Lab Test Requested (file of inspection report text recommendation)
... HEAT.031 - Asbestos - material unconfirmed; choice of treatment affects. costs

If the asbestos-suspect material seen in a building is confirmed as actual asbestos or an asbestos-containing product, depending on its condition and location, treatment ranges from doing nothing to complete removal.

Professional asbestos removal would involve significant costs and is the recommended course of action where asbestos materials are damaged, friable, in a location subject to damage, in an occupied space, and/or in an unoccupied location where asbestos debris is likely to be carried into occupied space by human traffic or by the operation of heating and cooling equipment.

A number of asbestos treatment options are available where asbestos material is found in a building. Choice of treatment can make a big difference in possible costs of handling the material. You should obtain proper technical information and health and safety guidelines before attempting to do anything with this material.

Asbestos in the Air Handler of Furnaces or Air Conditioners

Asbestos in furnace blower compartment (C) D FriedmanAmong asbestos products used in heating or air conditioning air handlers and blowers, we suspect that VIBRATION DAMPENERS, especially in undamaged condition, are likely to release much lower levels of asbestos particles into the HVAC system air than the softer insulating materials found in some air handlers themselves.

We have observed friable asbestos inside older warm air heating furnaces made by Williamson (corrugated asbestos paper insulation inside the air handler of an older unit) and by Armstrong (asbestos insulation around the flue vent connector passage through the air handler's blower compartment side wall - photo shown at left), and in some other brands of heating equipment.

But in our OPINION even in the air handler, depending on the size or amount, condition (undamaged), and location, the release into building air of asbestos from these sources may be very difficult to detect - suggesting that in those cases it is at very low levels, below measurable effect.


References for Asbestos Paper Duct Wrap

  • Abatement, Traditional Asbestos. "section 02 82 11 Traditional Asbestos Abatement." In Specifications For Bldg# 1, 5th Floor/sleep Clinic/bldg# 16 Conf., p. 259864. 2012.
  • Abatement, Asbestos. "SECTION 02.82. 00 ASBESTOS ABATEMENT."
  • Abatement, Asbestos. "1.1. 3 Related Work." Issued For Construction Documents Va Project No. 523a5-12-308 Date: 07/13/11 (1911).
  • "Asbestos in the Home", U.S. EPA, Education/Safety-Guides/Home/Asbestos-In-The-Home/
  • "Asbestos, a Guide for New Jersey Residents", State of New Jersey Department of Health & Senior Services, retrieved 5/1/14, original source:
  • Barman, Waldemar J. "Air conduit." U.S. Patent 2,108,159, issued February 15, 1938.
  • Froehlich, Phillip A., and Bruce A. Hollett. "Evaluation of glove bag containment and asbestos abatement clearance: Methodologies for asbestos removal." Applied Occupational and Environmental Hygiene 8, no. 11 (1993): 937-944.
  • Hunting, Katherine L., and Laura S. Welch. "Occupational exposure to dust and lung disease among sheet metal workers." British journal of industrial medicine 50, no. 5 (1993): 432-442.
  • Marc, Henri M. "Manufacture of ducts." U.S. Patent 2,434,465, issued January 13, 1948.
  • Oberta, Andrew F. Asbestos Control: Surveys, Removal, and Management. Vol. 23. ASTM International, 2005.

Also see these articles on asbestos in buildings

  • ASBESTOS HVAC DUCTS - Guide to Identification of Asbestos Materials On or In Heating and Cooling Duct Work: carbon monoxide hazards of transite chimneys and vents
  • ENVIRONMENTAL HAZARDS - INSPECT, TEST, REMEDY - Environmental Hazard Detection, Testing, Repair, Illness, Symptoms, & Prevention in buildings
  • IDENTIFICATION of ASBESTOS in buildings - Asbestos Identification in buildings: How to find & identify asbestos-containing materials
  • TRANSITE PIPE AIR DUCTS - Hazards of Asbestos-containing Transite Pipe HVAC Ducts: duct collapse, mold, radon, asbestos fiber release
  • TRANSITE PIPE CHIMNEYS & FLUES - Guide to Identifying Asbestos Transite Chimneys & Flues & their Hazards in buildings
  • TRANSITE PIPE WATER SUPPLY PIPING - Guide to Identifying Asbestos Cement Transite Water Pipes & their Hazards in buildings
  • VIBRATION DAMPENERS - asbestos gaskets and vibration dampers in duct work

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