Photo of tranite cement-asbestos material used for air ducts in a slab over a sewer pipe (C) Daniel Friedman and Conrad Hazards of Asbestos-containing Transite Pipe HVAC Ducts

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Transite HVAC air ducts:

This article explains the potential hazards of transite (cement asbestos) air ducts - asbestos fiber release, radon, and indoor air quality concerns, and duct collapse when transite air ducts are is found in buildings.

Transite pipe, an asbestos-cement product, was used for HVAC ducts and for chimney or flue material to vent gas-fired appliances.

Cement-asbestos transite pipe may also have been used for water piping in some communities. We discuss how to identify cement asbestos transite air ducts, what the safety & health hazards are, how to seal or abandon the ductwork, & alternative approaches.

This document assists building buyers, owners or inspectors who need to identify asbestos materials (or probable-asbestos) in buildings by simple visual inspection.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Transite Pipe HVAC Ducts: Asbestos Heating or Air Conditioning Duct Material Warnings

Photograph of transite cement asbestos heating duct

Transite pipe, which contains significant percentage of asbestos fibers, was often used for heating ducts and on occasion heating and cooling ducts in older buildings. Transite pipe used as HVAC ducts or air ducts for heating and air conditioning was often installed buried in a concrete floor slab - methods that placed the asbestos-cement transite piping below or in a building floor slab.

Asbestos-containing transite pipe HVAC ducts were also used in exposed areas such as shown in the crawl space photograph at the top of this page. And transite pipes were also used as flues or chimneys for some heating equipment, usually where gas fired heaters were installed.

Definition & Composition of Transite materials

While the term "transite" has been used to describe many asbestos-cement products (pipes, ducts), Transite™ is the trademarked name used by Johns-Manfille for asbestos-cement products that were manufactured by that company to its own specifications.

Those specifications varied by individual products but typically included a mixture of 15-25% chrysotile asbestos, 45-55% portland cement, and another 25-35% silica "flour" (that I read as finely-ground sand).

We emphasize that while Transite™ pipe materials, if they have not been painted nor exposed to the weather, usually will display a black stencil-stamp identifying the company and product, for example "JM-TRANSITE-FLUE", many other asbestos-cement products of similar formulation were produced by other companies including Celotex, CertainTeed, GAF, National Gypsum, and others. See ASBESTOS PRODUCING COMPANIES.

Article Contents

Transite air ducts in slabs often collect water, mold, pathogens. We provide photographs and descriptive text of asbestos insulation and other asbestos-containing products to permit identification of definite, probable, or possible asbestos materials in buildings.

The photo (above-left) of a sewer line routed immediately below a transite asbestos in-slab floor heating duct was provided courtesy of reader Conrad.

This case is illustrated in more detail

While an expert lab test using polarized light microscopy may be needed to identify the specific type of asbestos fiber, or to identify the presence of asbestos in air or dust or water samples, many asbestos-containing building products not only are obvious and easy to recognize, but since there were not other look-alike products that were not asbestos, a visual identification of this material can be virtually a certainty in many cases.

Photo of tranite cement-asbestos material used for air ducts and for heating vents (C) Daniel FriedmanReaders should also see:

Also see Micro-Photographs of Dust from the World Trade Center collapse following the 9/11/01 attack. Links to U.S. government and other authoritative research and advice are included.

[Page top photo of transite duct material courtesy of Thomas Hauswirth, a Connecticut home inspector.

Transite-type HVAC or Air Duct Asbestos Warnings & Hazard Details

Transite ducts used for HVAC air flow, especially when used buried in building concrete floors or slabs, may break, collapse, leak water in (forming a mold and bacterial reservoir in the HVAC system, or may release asbestos and other particles in building air when the HVAC system is operating.

An up-flow or down flow furnace in a building with concrete slab and with perimeter duct work raises some important health and cost questions:

The photograph above shows a transite cement asbestos heating duct in a carpeted floor slab. We recommend that in-slab heating or air conditioning ducts made of transite be sealed and abandoned, and alternate heat sources installed. This improvement removes an asbestos hazard, a flooded duct and mold hazard, and in some locales, also a radon gas entry point.

The photograph shows the edges as well as surface of the transite material. Transite pipe HVAC ducts get quite dirty and are not always easy to identify. [Photo and comments on transite in-slab HVAC ducts courtesy of Roger Hankey, a Minnesota home inspector.]

Loose blower assembly pulley or belt reduces airflow Carson Dunlop Associates

SLAB DUCTWORK - catalogs the functional and environmental problems found when HVAC air ducts are routed in or below floor slabs

Photo of tranite cement-asbestos material used for air ducts in a slab over a sewer pipe (C) Daniel Friedman and Conrad

Incorrect spellings of transite asbestos piping or transite duct material that we've seen include transit pipe, transit ducts, transite chimneys, transide pipe, transide ducts, and transight pipe or transight ducts. "Transite" is the correct spelling.

Recommendations where Transite Asbestos HVAC Ducts are Installed

Water and rodents in air duct © D Friedman at Apply an internal transite HVAC air duct sealant

There are also duct-sealants that some contractors offer as an in-duct sealant/spray. The contractor extends a spray wand into the HVAC ducts to deliver a coating that, if perfectly successful, can prevent or at least reduce the risk of asbestos fiber release into the building air.

And Andrew Oberta has described standards methods for repairing asbestos-cement products including underground transite piping.[5]

A down-side with in-slab ductwork is the difficulty in accessing for application of the spray and difficulty in inspection in the future to see what's going on inside the duct: collapsing walls, sealant falling off of duct interior, flooding, mold, asbestos-releasing scraps, rodents, etc.

Our in-slab air duct photo (left) shows evidence of a history of floods in the duct system as well as rodents (the rodent poison).

A second concern is that even if the coated transite air duct interior surfaces appear to have been treated successfully, especially with in-slab ducts we are not assured that the in-slab ducts remain clean, dry, and undamaged in the future nor that the transite duct interior coating remains bonded to the duct surfaces.

But given the history of concerns with the product, in particular with in-slab ducts, we would give strong consideration to abandoning in-slab ductwork entirely.

Abandon in-slab and other transite asbestos HVAC air ducts

In-slab air duct abandoned & sealed (C) Daniel Friedman

We recommend abandoning in-slab HVAC air ducts, including transite asbestos cement HVAC ducts, reasoning that there are multiple indoor air quality and potential health as well as functional concerns with such installations.

We described concerns with ductwork run in floor slabs in the article above, including risks of air duct collapse that interferes with air flow through the system, water leaks into the in-slab duct system (not a problem unique to transite ducts), and rodent or insect infestations or even mold contamination.

Odor complaints may be traced to the duct system because of these problems (DUCT & AIR HANDLER ODORS).

At SLAB DUCTWORK we give details about abandoning in-slab HVAC ductwork. That article also catalogs the functional and environmental problems found when HVAC air ducts are routed in or below floor slabs.

When abandoned, in-slab ductwork of any material can usually be left in place.

However where radon gas is an issue, we seal the ducts at the air delivery registers in the building floor slab, as well as sealing any slab cracks that may allow radon gas to enter the building at increased levels.


Continue reading at TRANSITE WATER PIPE ASBESTOS RISKS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see ASBESTOS CEMENT PRODUCTS - home, where we include research on the chrysotile asbestos content & hazard of asbestos cement & transite products.

Or see these

Transite Pipe Articles

Readers concerned with ice or water leaks into or out of HVAC ductwork should also see WET CORRODED DUCT WORK

Suggested citation for this web page

TRANSITE PIPE AIR DUCT ASBESTOS RISKS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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