How to Identify Asbestos in Heating Ducts

By Stan G. in Removal

From the mid-1950s through the early '80s, sheet metal air ducts for forced-air heating systems were commonly insulated with a cardboard-like material that contained asbestos fibers. In some cases, a careful, close examination is necessary in order to determine whether these old heating ducts are composed of asbestos or merely insulated with it.

Also, look to see if the asbestos or insulation material is breaking or coming apart. If the material is undamaged, securely attached, and not exposed to routine contact, it does not pose a health risk.

Asbestos Paper Wrap or Tape Used to Seal or Insulate Heating Ducts

Duct tape is a white, flat material that was applied to air ducts to seal gaps and reduce air leaks. With a fibrous appearance, asbestos-containing duct tape usually contains high levels of asbestos and is dangerous to disturb. Generally, it is thicker than modern duct tape, white or grey in color, and simply peeling it off a surface can cause asbestos fibers to become airborne.

The asbestos-containing duct tape that was used by the HVAC industry to line and insulate pipes in heating and cooling systems within homes typically contains between 35 - 65% chrysotile asbestos. For a comprehensive evaluation of your air ducts to determine their level of safety and functionality, it is recommended that you consult a certified asbestos inspector.

If You Live in an Older Home, Make a Visual Check of All Accessible Ductwork for Damaged Insulation

In older homes, it is common to find asbestos in heating ducts on the interior and exterior surfaces, especially around bends and connections, for example, asbestos duct dampeners - asbestos-containing woven material - that was used to create flexible joins between heating ducts or between an air handler and ductwork.

If you come across ductwork in your property and know that it was installed pre-1970, the best practice is to assume that it may contain asbestos. On older homes asbestos paper-like material was often wrapped around the entire duct exterior rather than simply at the joints.

Manufacturers of asbestos-containing heating ducts:

  • W.R. Grace Corporation
  • J-M Manufacturing Company, Inc.
  • Rich Tex Inc.
  • Georgia-Pacific
  • Celotex
  • Duro Dyne Corporation
  • Grant Wilson
  • H.B. Fuller
  • Johns Manville
  • Nicolet
  • Turner & Newall

Does Asbestos Duct Tape Require Replacement?

The material itself can become hazardous when it releases fibers into the air due to damage, disturbance, or deterioration over time. If the ducts become punctured or torn, asbestos fibers can be released into the air stream. In that case, repair or removal would be advisable.

Encapsulation is often the best option when dealing with insulation on heating systems. A few inches of torn, loose, or frayed asbestos tape-wrap on heating ducts can be sealed with a coating material. Damaged hot water pipe insulation can be covered with a special fabric available at safety equipment stores.

In cases there's extensive asbestos damage or disturbance, removal may be the more appropriate, and the only option. If you decide to remove asbestos duct tape yourself, follow these steps to do so as safely as possible:

  • Seal off the work area with multiple layers of plastic sheeting held in place with heavy tape and staples
  • Set up a three-stage airlock, and depressurizes the work area with specialized air handlers
  • Enter the work area with air supplied respirators and protective clothing
  • Wet down the duct tape, carefully scrape it off, and seal it in doubled plastic bags

For more information, we recommend you read our Asbestos Removal page.

Why Should I Test Products in My Home for Asbestos?

It is often impossible to tell whether asbestos is embedded in a material, as the fibers are too small to be observed with the naked eye. Exposure to asbestos is responsible for serious respiratory conditions, so thorough testing is required to ensure your home is asbestos-free.