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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.
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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.
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.]
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.
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.
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 (SLAB DUCTWORK) 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.
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Frequently Asked Questions (FAQs)
Question: can I seal a crack in a transite HVAC duct?
Can a crack in a transite HVAC "duct" be sealed or repaired. I am having foundation issues with my slab on grade living room and one of the ducts is cracked. - Brad 8/6/11
Brad transite is a cementious product. It could be "repaired" using a bonding agent and high-portland content patching cement, and perhaps even duct seal.
Question: Water leaked into our transite air ducts - is this a problem?
I had some water get into my transite pipe buried into the slab of my house. I stopped the water by putting a new cement slab and redirecting the water. I immediately dried it up with a wet vac and kept the air conditioning on. I obviously have a leak in the pipe and have noticed some debris which I had removed by a HVAC vacuum company. I was told by an inspector when I bought the house that the transite probably had asbestos. Is this a problem? What should I do ? - Jack 9/22/12
Jack: I'm not sure which concern or problem you were asking about.
Basically if you abandon an in-slab transite pipe duct and seal the floor (you added another layer of concrete over your original floor slab) so that it can't easily send radon, rats, or mold into the building, it's not much of a concern - the cement-asbestos material won't move up through the new slab and thus won't be an ongoing asbestos hazard.
Your inspector, by saying that transite "probably had asbestos" was perhaps trying to please the seller and real estate agent from whom s/he receives referrals. Transite HVAC ducts are a cement-asbestos product and contain about 50% asbestos materials (fibers and powder filler) by volume.
Because it's in a cementious form the transite duct material is not normally friable so is less likely to release significant levels of asbestos into building air than softer asbestos materials such as asbestos pipe or boiler insulation. But when water-damaged or mechanically damaged, the asbestos release hazard from transite ducts can increase significantly.
What should a homeowner do about a transite air duct system? Is it a health hazard? I have two 12 - 15 foot lengths of HVAC ducts under a slab portion of my home. The ducts look to be in good shape through visual inspection from the floor vents with the exception of one crack (see post and answer below). If I want to stop using the ducts, what should I do as far as sealing them off from the furnace? I have installed a gas burning insert in the room so I can get away without using the ducts. Any help would be greatly appreciated. - Brad 6/11/12
If you abandon use of a transite duct, and provided it's not damaged so as to have become friable (releasing dust, easily crumbled between your fingers) it can be left in place - it's not "radioactive" - and is better left undisturbed. Don't run power tools, saws, grinders, etc. on cement asbestos material. But in the article above we give some reasons why in-slab air ducts of any sort present indoor air quality risks and hazards from future and un-discovered flooding, rodents, mold, etc. Add to that the risk of softening (asbestos fiber release) from water or moisture condensation in the ductwork, and the collapse risk. I'd prefer to abandon the in-slab ducts (SLAB DUCTWORK) and seal off those supply registers.
With that approach, and as long as there are not other slab cracks that leak contaminants into the building, it may not be necessary to try fill the entire in-slab duct with cement or other fillers, and the material can safely be left in place.
Questions & answers or comments about transite air ducts: asbestos cement air duct issues.
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