Photograph of  asbestos paper wrap on heating/cooling duct exteriorAsbestos HVAC Ducts & Furnaces
Identification & Assessment of Asbestos In Heating and Cooling Duct Work & Air Handlers

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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.

Page to photo: white asbestos paper used as an insulating wrap on old metal air ductwork.

Green links show where you are. © Copyright 2017, All Rights Reserved.

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

Photograph of asbestos paper duct sealThis 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 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.

Article Contents

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

Asbestos - Ductwork Types & Materials

Photograph of asbestos paper duct sealAnother 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

Photograph of  asbestos paper wrap on heating/cooling duct exterior

Asbestos fiber release and carbon monoxide hazards

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 - see 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 where we provide additional photographs of this material.

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 TRANSITE PIPE AIR DUCT ASBESTOS RISKS

Photograph of  asbestos paper wrap on heating/cooling duct exterior

Asbestos On or In 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 the mere presence of this material in residential buildings, it is generally considered by the scientific community to be a potential health risk if building occupants are likely to be exposed to significant levels of airborne asbestos dust.

If there is asbestos paper wrap on the exterior of HVAC ducts the risks are low, as we will explain below.

Watch out: If there is asbestos paper or a corrugated asbestos insulation liner inside of HVAC ducts that is likely to be hazardous. Such ductwork should be removed intact (by a qualified contractor) and replaced.

Watch out: demolition or removal of asbestos-covered or asbestos-lined HVAC ducts requires use of appropriate asbestos removal procedures including containment of the dust and debris and steps to avoid building cross-contamination into other areas.

The asbestos paper "insulating" duct wrap such as shown in several of these photographs is typically 55% chrysotile asbestos (as defined in OAR 340-248-0010(5)). Contractors who remove such ductwork without following proper procedures may be liable to civil penalties and litigation. (Oregon DEQ to Gelber 2016).

Economic Impact of Asbestos on or in HVAC Ducts

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.

Suggestions for Handling Asbestos On or Inside 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 the Exterior of HVAC 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.

    Often intact asbestos-paper-wrapped air ducts might be left in place and encapsulated by a suitable paint, coating, or wrap.

    Exterior asbestos paper duct wrap or tape that is damaged or disturbed presents a risk of asbestos contamination.

  2. Asbestos on the Exterior of HVAC 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 HVAC Ducts 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 opinion such asbestos-lined ducts or air handlers should be replaced.

    The removal of any insulation inside of a furnace can make the heater unsafe, risking over-temperatures, equipment damage, flue gas leaks, even fires. Where we encountered this situation the furnace manufacturer would not warrant the heater when its insulation was modified in the field.

    There are spray-in coating "solutions" sold for HVAC ducts that purport to create a new duct interior liner. In my OPINION I'm uncertain about the long-term safety and reliability of spray-in duct liners. In virtually all HVAC systems it is very difficult if not impossible for a building owner or manager to regularly inspect the interior of the ductwork. Such inspection requires cutting of openings and use of a duct inspection camera system.

    One cannot be sure that the spray adequately reached and covered all of the duct interior. One also cannot be certain that some section of that spray-on coating has not later fallen away from the duct interior when the interior asbestos duct insulation to which it was applied itself falls away.

    Building occupants are left thinking that a safety hazard has been addressed when it may in fact be a continuing hazard.

What to Do about Asbestos-Wrapped HVAC Duct Exteriors

[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 Inside Metal HVAC Ducts for Air Conditioning & Heating Systems

Possible asbestos paper reinforced with jute inside of an HVAC duct (C) TinaQuestion: do you think this metal duct interior liner is asbestos?

I am getting different opinions on [whether or not ] my duct work [contains an asbestos paper liner].

Do you think [this duct uses ] aspestos ?

And if it is asbestos is it dangerous?

The home where this ductwork was installed was constructed in New Jersey in 1967.

Thanks -Anonymous by private email 12/12/2017

Reply: corrugated asbestos paper used as liner in metal HVAC ducts

I think I see metal ductwork on the floor of an attic of an older building.

Your first photo shows metal ductwork that is crushed and bent. In that condition it's not usable and may not be safe.

Possible asbestos paper reinforced with jute inside of an HVAC duct (C) Tina

I zoomed in to see as much as I could of the duct liner in the second of your photos that I will show below.

It's uncommon to find hemp (burlap) reinforced corrugated asbestos paper insulation inside of metal ductwork but that is certainly what it looks like to me.

And indeed in the U.S. the Illinois DEC indicates that asbestos was used as both an insulation and an air leak sealant both on the exterior of HVAC ducts and in the duct interiors.

It would be helpful to have more information including the country and city where the building is located, whether this is a private home or something else, and the age of the home. I'd also like to see a photo of the furnace but I suspect it's long gone.

Usually one can not say for certain whether a material is asbestos or not without a lab test. But there are some cases where there was no non-asbestos look-alike product.

Possible asbestos paper reinforced with jute inside of an HVAC duct (C) TinaOne of these is asbestos insulating paper which is gray, has a characteristic texture and is flat where used on the outside of hvac ducts and also is in a corrugated paper form on piping. You can see some examples at

ASBESTOS PIPE-INSULATION - this article shows corrugated asbestos paper (used here as a pipe wrap) that you will see virtually duplicated in pattern in the corrugated paper exposed at the left end of the duct section in your photo.

ASBESTOS PAPER DUCT INSULATION - this article shows the use of flat asbestos paper on duct exteriors.

In any event, rather than face a costly asbestos removal project to modify the duct work, what I would expect any sensible contractor to suggest is something that' needed in any event, regardless of the duct insulation: the duct you show is crushed, damaged, not usable.

It would make sense to bag and remove the duct sections intact, with as little disturbance as possible.

If your heating system needs to run ducts through an attic space it would make sense to install new metal ductwork with exterior insulation.

Watch out: What makes us asbestos a health hazard or not depends on the exposure of people in the building to asbestos dust. I can see that some of the ductwork has already been removed as your photo shows it on a porch floor. And I agree that such damaged ductwork should be properly removed from the home.

If in the removal of this damaged ductwork the remediator is not creating a dusty mess then the risk levels are very low.

That's why when you are removing old ductwork that appears to contain asbestos you want to do it by taking out intact duct sections rather than doing anything aggressive (chopping, sanding sawing) that creates a lot of dust.

Advice if Asbestos Has Been Released In Your Building

The following is excerpted from advice from the Oregon DEA

‚ÄčIf you think a significant amount of asbestos has been released in your home:

Health impacts that are typically associated with being exposed to asbestos comes primarily from working for long periods of time around very high concentrations of fibers. Your health should not be impacted by a single exposure to asbestos fibers, but if you are concerned, please consult your doctor. - (Oregon DEQ 2017)

Research on the Use of Asbestos Liners In HVAC Ducts

Supporting research confirms that there were asbestos paper duct liners made with reinforcement of hemp

Watch out: the U.S. Environmental Protection Agency previously provided various asbestos remediation and removal or encapsulation guidelines but as of December 2017 an online search for commonly-indexed documents is producing hung connections - you may be able however to obtain printed copies from your local EPA office.

Example of US EPA Asbestos Documents Not Loading: Guidelines for Asbestos: NESHAP Demolition and ... - epa nepis

Asbestos inside or at 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.

Below 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.

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

References for Asbestos Paper Duct Wrap & Duct Asbestos Hazards

Example Home Inspection Report Text on Asbestos on Heating Equipment

These are examples of additional text used in home inspection reports where asbestos material is observed:

HEAT.030 - Asbestos Materials on Heating System - Summary

Safety Recommendation: We observed what may be asbestos containing insulating material on the the heating distribution system.

Do not disturb the material and do not allow others who are not trained and qualified to disturb or attempt to remove it.

Improper asbestos removal efforts can create health hazards by contaminating building areas with asbestos dust and debris.

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 asbestos containing material (ACM) 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.

Usually the lowest risks from asbestos in a residential building where the material is in good condition is to leave it in place and to encapsulate or cover it.

Typical examples of uses of asbestos on residential heating systems include

Depending on condition and location of asbestos material, treatment ranges from doing nothing to encapsulating it to complete removal. Removal and disposal of asbestos in buildings can involve a significant expense.

HEAT.031 - Asbestos - material unconfirmed; choice of treatment affects costs

If the material is confirmed as asbestos, depending on its condition and location, treatment ranges from doing nothing to complete removal.

Removal would involve significant costs and is generally the preferred course.

A number of treatment options are available. 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.810 - Improper/Incomplete Asbestos Removal - Warnings

Watch out: A considerable amount of this asbestos or asbestos-suspect insulating material has been removed.

Removal has not followed approved methods and procedures: we saw that piping has not been cleaned nor sealed, and that the suspect material has been left in some places - details not found when materials were removed by trained professionals.

Unprofessional removal of controversial materials in a building may raise health, legal, or marketing concerns for future property owners. You should attempt to obtain documentation regarding who did what to the property regarding this topic. Additional testing to assure that no hazards or legal issues remain, may involve significant expense. <$ISignificant expense;possible, hazardous materials>


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