Photograph of  asbestos paper wrap on heating/cooling duct exteriorAsbestos HVAC Ducts & Furnaces
A Guide to Identification & Hazard Assessment 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. What to do about asbestos on heating or other air ducts in buildings.
  • 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.

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 ASBESTOS CHIMNEYS, DUCTS, PIPES.

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.


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 DUCT ASBESTOS RISKS

ASBESTOS RISKS - on Heating and Cooling Ducts

Photograph of  asbestos paper wrap on heating/cooling duct exteriorAsbestos on Ducts, Health Concern: While 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 on Ducts, Economic Impact: 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

Action Suggestions for Asbestos-Wrapped Air Ducts on Heating or Cooling Systems

Asbestos fabric or reinforced paper on a heating duct and supply register (C)  SU 2016
  1. Asbestos on supply ducts: When asbestos paper or fabric is on the outside of an air supply duct, that duct is, with respect to the asbestos covering, never sucking asbestos fibers IN, it's only trying to blow them AWAY - and that only IF the wrap is covering actual leaks or holes in the ductwork. So the risks in that direction are small.

    My expectation and thus OPINION in this case is that the level of airborne asbestos in the building and that could be attributed to this particular asbestos source is most-likely to be below the limits of detection. However if the material is in a location where it can be damaged and/or spread into occupied space it needs to be addressed, as described below.
  2. Asbestos on return ducts: If there is asbestos wrap on the outside of HVAC return ducts, as those may be under negative pressure, if there are openings in the ductwork covered by loose or damaged asbestos material, asbestos could be drawn into the HVAC system and redistributed into the occupied space - a potential hazard.

    I would consider removing such ducts and replacing them as described below.
  3. Asbestos inside of duct work or air handlers: If there is asbestos material in the actual air path such as inside HVAC ducts (which is rare) or inside the actual HVAC air handler (which was true on some older furnaces) then that is much more likely to be a source of hazardous levels of airborne asbestos in the building.

    In my opinoin such ducts or air handlers should be replaced. There are spray-in coating "solutions" but I'm not sure about their long-term safety and reliabilty.

What to Do about Asbestos-Wrapped HVAC Ducts

[OPINION - as this advice would change when informed by specific site conditions]

IF the asbestos material is not falling off and creating a mess,
IF the asbestos duct wrap material is not in a location where it's likely to be banged, moved, damaged (thus creating a hazard) and it is not in the air path of the HVAC equipment


You can leave it in place, coating it with a spray-on paint, coating, or wrapping it if it's in a location where it can be wrapped with any suitable duct seal, even aluminum tape.


[this means there is probably a reason to remove the asbestos material]

The least disruptive and least expensive way to remove the material is to work carefully to remove the ductwork itself that is covered in asbestos, in intact sections, with absolute minimum number of cuts or disturbances, for bagging and disposal.

That process is perhaps done by a professional using negative air control to avoid cross contamination, proper bagging and legal disposal, followed by damp wiping and HEPA vacuuming to remove any questionable dust.

If You Are Facing A Significant Asbestos Insulated Duct Abatement Project Cost

First: confirm that the material is indeed asbestos and that its condition or location requires its removal.

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.

Exhaust flue passing through return air plenum: a warning

Watch out: if there are corrosion leaks or any other openings in the flue vent connector where it passes through the furnace return air side, depending on the blower location several very dangerous conditions can occur, including carbon monoxide production at the burner due to back pressure, or the reverse: negative air pressure (such as will occur in the furnace shown) when the blower is running can extract combustion gases right out of the flue and draw them into building air being passed through the furnace heat exchanger.

References for Asbestos Paper Duct Wrap

Asbestos HVAC Duct Articles


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