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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.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

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.

AC pipe was typically made by adding chrysotile and/or crocidolite asbestos, ranging from 10 to 75 percent, to Portland cement, water and silica. ... AC [Asbestos Cement] pipes usually contain anywhere from 10 to 75 percent asbestos. (McKenna 2016).

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.

Asbestos-cement HVAC Ducts & Airrborne Asbestos Risk?

A preliminary study performed by the New Jersey Department of Health (1986) on a small number of homes found that in some homes asbestos-cement (transite) HVAC ducts can result in unacceptably high airborne asbestos hazards.

That is not to say that every home with asbestos-cement ductwork is dangerous, and we infer from the study and other research that the several factors probably increase the indoor asbestos hazard in such homes, including particularly the condition of the transite pipe ducts, the use of the HVAC system and its condition, and general housekeeping.

In our OPINION there are both potential airborne asbestos hazards associated with asbestos-cement ductwork and also mold and other health hazards from ducts in slabs in general, sufficient that an evaluation of such buildings and (possibly) remedial action are warranted.

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 & TRUSTS.

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

at CAST IRON DRAIN PIPING.

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.

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

Photo of tranite cement-asbestos material used for air ducts and for heating vents (C) Daniel FriedmanTransite 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 some of our comments on transite in-slab HVAC ducts are provided 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 InspectApedia.com

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.

See SLAB DUCTWORK

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

See details at 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.

Research on Hazards of Cement-Asbestos Transite HVAC Ducts

Asbestos properties in McKenna 2016, cited & discussed at InspectApedia.com about transite asbestos pipe & ductwork

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2022-08-20 by InspectApedia-911 (mod) - repair to damaged asbestos-cement (suspected) HVAC air duct in slab?

In-slab ductwork, damaged, MIGHT be transite asbestos-cement - (C) InspectApedia.com Sam Labaidi@Sam lababidi,

With apologies because I don't intend this to be glib, just about anything is "repairable" - the questions are about cost, benefit, and perspective.

It's certainly possible to patch in a section of PVC or similar duct material for a damaged in-slab transite air duct.

See Oberta (2004) cited at the end of the article above.

But as I ask you to read in this article series, there is such a long history of problems with in-slab HVAC ducts that spending on repairing such a duct system is in our opinion, questionable. You may be throwing good money after bad.

Those issues are explained more-fully at SLAB DUCTWORK inspectapedia.com/aircond/Ducts_in_Slabs.php

On 2022-08-20 1 by Sam lababidi

Is there anyway to repair this air duct?

On 2022-08-18 by InspectApedia-911 (mod) - Transite ductwork? Damaged asbestos-cement (suspected) HVAC air duct in slab

@sam lababidi,

That could be transite pipe (asbestos cement) - though one can't say for dead certain from a photo, by building age and context that's a reasonable guess.

I hope you'll take a read through the article above for advice and opinion; ask any follow-up questions you need.

On 2022-08-18 by sam lababidi

My plumber is replacing the sewer line under my slab. While doing so he damaged an cement air duct in the ground. Can anyone tell if this is asbestos pipe.

[See photo above, in this conversation - Ed.]

House was built in the 1955.

On 2020-09-29 by danjoefriedman (mod)

Anon:

Thanks for a helpful question about condensation inside in-slab ductwork.

I don't think you can assure that there will not be rust in a metal duct installed in an RCC (Reinforced Concrete) slab;
The rust sources or really moisture sources extend beyond leaks into the duct system to include condensation problems and the fact that the slab won't be drained.

You'd need to use a non-metallic ductwork such as PVC, and even then, avoiding rust doesn't mean avoiding moisture and mold troubles.

Back to metal in-slab ductwork condensation and rust:

However insulating the ductwork exterior during construction and building a slab that's above grade level and protected from ground water entry would reduce those risks, as would
careful attention to catching any condensation in the air handler and draining that properly. A high indoor RH (relative humidity) level and the cooler temperature of the in-slab ductwork make condensation therein likely and so rust an ongoing risk, along with mold once there is a bit of organic dust in the slab system.

See details at SLAB DUCTWORK https://inspectapedia.com/aircond/Ducts_in_Slabs.php

On 2020-09-29 by Anonymous

How to prevent a duct in an RCC slab

from rust


...

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