Cement Flue Pipe and Cement Board Products

Why this matters

A gray, stone-hard pipe running from an old water heater or furnace into the chimney looks like the most harmless thing in the basement. So do the stiff gray siding shingles on a 1950s house. Both are often asbestos-cement, a material that is stable and low-risk while it sits whole, and that releases fibers the moment it is broken, cut, drilled or sanded. Every one of those verbs is in a water heater swap, a dryer vent, a line set penetration or a siding repair. The plumber who knocks the old flue loose with a hammer to get the heater out has created the exposure the material had kept to itself for sixty years.

What asbestos-cement is

Asbestos-cement is portland cement reinforced with asbestos fibers, pressed or formed into pipe, sheets, panels and shingles. The fibers made thin sections strong and fire-resistant, which is why it was used for flue pipe, siding and heat shields. The trade often calls it transite, after a historical product line, and uses the word for any of it.

It was common from roughly the 1920s into the 1970s, with some products made later. Like everything on the legacy map, a date is a likelihood, not a verdict. See related: Dating a House by What You Find in It.

The property that matters most: it is hard and bound while whole. The fibers are locked in the cement. Intact, unweathered asbestos-cement releases very little. That is why the EPA's asbestos rules treat intact asbestos-cement products as non-friable (not crumbled by hand pressure) while they stay that way, and why they become a regulated release once they are broken, ground, sanded, cut with power tools or reduced to rubble. The material's risk is almost entirely in what someone does to it.

How to recognize it

Flue pipe and vent connectors.

• Gray, cement-colored, often with a slightly rough or mottled surface that looks like a sidewalk, not metal.
• Thick-walled compared with a sheet-metal connector, and dull rather than shiny.
• Joined with cement or a cement-like collar rather than screws, crimped ends or foil tape.
• Often 3 to 6 inches in diameter, running from the draft hood of a gas water heater or a furnace into a chimney thimble, sometimes inside a chimney as a liner.
• Tap test is not allowed. Do not knock on it with a tool to hear whether it rings like metal; that is the disturbance.

Siding shingles and panels.

• Stiff, flat, brittle gray or painted shingles, often about 12 by 24 inches, with a textured or wavy face that imitates wood grain or a pebbled finish.
• Pre-punched nail holes along the lower edge, nails exposed at the bottom of each shingle.
• Broken corners that show a gray cement core with a fibrous look.
• Very different from modern fiber-cement siding, which is common on houses built since the 1990s. Modern fiber-cement uses cellulose fiber, not asbestos, and is installed as long lap boards or panels. If the house's age and the product's shape do not settle it, record what you see and route it.

Boards and heat shields. Gray cement board behind an old wood stove or a space heater, inside some old electric heaters, or lining a furnace closet.

Why the hazard lives in your verbs

OSHA's construction asbestos standard (29 CFR 1926.1101) classes asbestos work by what the worker does to the material, not by what the material is. For an employer whose employees will touch it, the classification sets the training, the supervision by a competent person, the wet methods, and the respiratory protection under a written 29 CFR 1910.134 program. Removing asbestos-cement siding, roofing or pipe that is not thermal system insulation falls in the standard's Class II category. A repair or maintenance task that disturbs it can fall in Class III. Your shop does not get to skip the standard because the job is small or the house is a single-family home.

So walk through the verbs of the job:

• Break (hammering loose a flue section, snapping a shingle off): releases fibers at the fracture and turns a whole piece into fragments.
• Drill (a hole for a dryer vent, a line set or a mounting bracket): grinds a cylinder of the material into dust at the bit.
• Cut (with a saw to shorten a pipe or fit siding): the highest-release act, especially with a power saw.
• Sand or pressure-wash (siding prep, paint removal): erodes the surface fibers and can wash them into the soil around the house.
• Remove whole (unscrewing a joint, lifting an intact section off): the lowest-release way to take it out, and still regulated work for your employees.

Pressure washing deserves its own warning for exterior trades: a high-pressure wand on weathered asbestos-cement siding strips the binder and releases fibers into the spray and the yard. A washing crew that meets it uses a low-pressure wash or declines the siding.

How a replacement job plans around an old flue

The most common meeting is a gas water heater replacement in a house where the vent connector from the old heater to the chimney is asbestos-cement.

The problem in one sentence: the old heater cannot come out without separating it from the flue, and the old flue cannot carry the new heater's exhaust without the plumber confirming its size and material are acceptable under the current fuel gas code and the new heater's instructions, which many old asbestos-cement connectors will not meet.

What goes in the plan, in order:

1. Identify and record the connector as "suspect asbestos-cement vent connector," with length, diameter, joints and condition. A cracked, crumbling or broken section is a higher-priority note, because it is already releasing.
2. Test or presume. Either a licensed asbestos inspector samples it, or the job presumes it positive. Presuming is often the quicker decision, because the pipe is coming out either way.
3. Abatement contractor removes it whole, wet, with the joint at the chimney thimble handled under their controls. The separation from the old heater's draft hood is part of their scope, not the plumber's, because that is where it breaks if anyone forces it.
4. Plumber installs the new heater with a new listed vent connector, sized per the heater's instructions and the fuel gas code as adopted locally, and checks the chimney's suitability (an unlined masonry chimney is its own question). See related: Unlined Chimneys, Coal Chutes and Unused Flues.

The worked example: a failed water heater in a 1968 house

The call. A water heater in a 1968 house is leaking from the tank. The homeowner has no hot water and a wet basement floor. The plumbing shop sends a tech for a same-day replacement.

First moves. The tech turns the heater's gas control to off and closes the gas shutoff valve to the heater, closes the cold-water supply valve to it, and routes the drain to the floor drain. Standing water is not near the electrical panel or any outlet. The tech then looks at the vent: a 3-inch gray cement-looking connector about 4 feet long, two sections joined with a cement collar, running from the draft hood into a masonry chimney thimble. One section has a hairline crack; no debris on the floor below it. The tech records it as suspect asbestos-cement and does not touch it.

The fork. Same-day replacement was the plan, and the vent connector stops it, because the old heater cannot be separated from the connector without risking breaking it, and the tech's shop has no asbestos program. The tech calls the office. The office has a working arrangement with a local licensed abatement contractor, who can be on site the next morning for about 2 hours.

Keeping the house safe overnight. The tech confirms the heater's gas valve is off and the cold supply is closed and the tank drained to below the leak, so no more water enters. Nothing on the heater is firing, so nothing is venting into the cracked connector. Before leaving, the tech walks the basement with a combustion gas detector around the heater's gas connection and valve to confirm nothing is leaking at the joint that was just closed. The family has no hot water for one night, which the tech tells them plainly, along with why.

The next day. The abatement contractor removes both connector sections whole, wet, and seals the chimney thimble opening temporarily. The plumber arrives after they leave, removes the old heater, installs the new one with a new listed vent connector and a new connection at the thimble, and checks the chimney for draft with the new heater firing.

Putting gas and fire back in. Before lighting the new heater, the plumber leak-checks every gas joint touched with a leak-detection solution, confirms the tank is full and the relief valve and its discharge pipe are installed, then lights it per the instructions. With the heater firing, the plumber checks draft at the draft hood, and checks for spillage there with a smoke source or a mirror and for carbon monoxide in the room with a monitor. A heater that spills is shut off and left off until the venting is corrected; it does not get left running "to see if it settles."

Time summary. The tech's first visit was about 1.5 hours including the shutoffs, the gas check and the record. Abatement was 2 hours the next morning. The replacement was about 3 hours. The same-day plan would have been 3 hours on one day, so the job took two calendar days and about 6.5 working hours across two contractors, not 3 hours across one.

What would have changed it. If the connector were sheet metal, this was a same-day job. If the old connector had been broken on the floor when the tech arrived, the first move would have been keeping everyone out of that part of the basement, not trying to tidy it, and the abatement contractor's scope would include cleanup. If the shop had a trained Class II crew under an asbestos program with a competent person, removing an intact connector whole might have been in-house work, under the standard's controls.

The siding version, briefly

An HVAC line set, a dryer vent, a hose bib or a satellite bracket through asbestos-cement siding is the same plan in miniature: identify, presume or test, avoid if you can (route the penetration through a trim board, a foundation wall or an existing opening), or have a qualified contractor remove a single shingle whole before the trade cuts the wall behind it. Never drill the shingle.

References

• 29 CFR 1926.1101, OSHA construction asbestos standard, for work classes and employer duties.
• U.S. EPA asbestos NESHAP (40 CFR Part 61 Subpart M) for how intact and damaged asbestos-cement products are treated.
• Your state asbestos program for licensing of inspectors and abatement contractors in homes.
• See related: Asbestos-Suspect Materials by Location in a House; How to Plan Work Around a Suspect Material You Cannot Test Today.
• See related: How to Inspect the Relief Valve Arrangement on an Old Heater.