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CHIMNEY SAFETY

Old Metalbestos chimney pipe: what the white rings mean

If your inspection found that your insulated chimney pipe is leaking its insulation at the joints, here is what that means, why it matters, and what to do about it.

By Patrick Krol · Tahoe Chimney & Fireplace

The short versionPlease stop using the stove until the chimney pipe is replaced. The danger is not the insulation itself. It is the empty air pockets left behind in the pipe wall, which let too much heat reach the wood around your chimney, and the open seams, which during a chimney fire can let flames out of the pipe.

What Metalbestos pipe is

Metalbestos is Selkirk’s brand of insulated, double-wall stainless chimney pipe (a “Class A” chimney). Older pipe of this type was “solid-pack”: the space between the inner and outer steel walls was packed with loose silica insulation, a fine white powder.

That insulation is what lets the chimney pass safely through ceilings, attics and roofs, only a couple of inches from wood framing. It keeps the outside of the pipe cool enough for the wood next to it.

Embossed Metalbestos Model SS marking on the outside of an older chimney pipe
The Metalbestos name stamped on an older pipe. Note the dark staining coming down from the joint above it.
Older insulated chimney pipe on a shingle roof with stained sections
An older insulated chimney above the roof. Discoloration at the joints is a warning sign.

What the white rings are

A healthy pipe is smooth stainless steel inside. When the inner wall separates at the joints, the silica insulation starts leaking out of the seams into the flue. Looking up the chimney, you see it as a white ring at each joint.

Looking up the inside of a chimney pipe with a white ring of leaking silica at a joint
Looking up the inside of the pipe: white silica leaking from a joint.
Another view up the flue showing a white silica ring at the next joint
The same white ring at the next joint up.

Why it’s dangerous: air pockets and hot spots

Every bit of silica that leaks out of a seam leaves an empty space in the wall of the pipe above it. The insulation settles down into the gap, and an air pocket forms higher up. Where there is an air pocket, nothing stops the heat. That spot on the outside of the pipe gets much hotter than it was designed to, and if wood framing, a ceiling joist or a roof board is close by, that wood takes the heat.

Insulated pipe is allowed just 2 inches from wood only because the insulation is there. Without it, 2 inches is not enough: wood needs 6 to 18 inches from an uninsulated pipe.

Cross-section of a double-wall chimney pipe: silica leaks out of a seam into the flue, leaving an air pocket above it; heat passes through to a wood stud 2 inches away, and in a chimney fire flames can escape through the seam
Inner and outer liners are about an inch apart, with the silica between them. When a seam opens, the silica drains out and an air pocket forms above it.
What pyrolysis is: wood that sits next to heat for months or years slowly dries out and breaks down chemically, until it can catch fire at a much lower temperature, with no flame or spark needed. It happens out of sight inside walls and ceilings. Read more about pyrolysis.

Hidden fire

A hot spot next to framing can start a fire inside a wall, ceiling or attic, where nobody sees it until it’s serious.

Sparks and flames at the seams

In extreme cases, a badly separated joint can let sparks or even flames out through the seam during a hot fire.

Deformed pipe

If the inner pipe is badly bulged or warped, smoke tumbles and cools, and creosote can build up much faster.

Black streaks on the outside of the pipe

When you see black streaks running down the outside of the pipe from a joint, the pipe has been breached. It means there was a chimney fire: the heat liquefied the creosote inside, and the pressure pushed it out through the seams. That creosote is acidic, so it eats at the steel as it runs down, and it is also flammable.

Insulated chimney pipes on a roof with black creosote streaks running down from the joints
Black creosote streaks running down from the joints.
Close-up of dark creosote staining below a pipe joint
Dark staining pushed out of the joint above.
Chimney cap and screen coated in black creosote
Heavy creosote on the cap and screen, another sign of past chimney fires.

What about asbestos?

“Metalbestos” is a brand name, and the name alone does not mean asbestos. In general:

1950s – 1970sThe insulation may contain asbestos. Asbestos pipe insulation was banned in 1975, and builders phased it out of construction materials by the early 1980s.
1980sLess likely, though leftover older stock was still sold and installed for a few years.
1990s and newerVery unlikely to contain any.

Either way, asbestos is not the main issue here. Sealed between two steel walls, the insulation stays put. The real danger is the air pockets and hot spots described above. When we replace the pipe, we remove the old sections carefully, keeping them intact and contained, so nothing is spread around your home.

What to do now

  1. Stop using the stove or fireplace until the chimney pipe is replaced.
  2. Don’t take the pipe apart or sweep up the white powder yourself. Leave it for us.
  3. Make sure you have working smoke and carbon monoxide alarms on every floor.
  4. Schedule the replacement. We carefully remove the old pipe and replace it with new insulated chimney pipe.

Questions about your chimney?

Call or text us and we’ll walk you through your report and your replacement estimate.

Call (530) 414-7600Book an inspection
Patrick Krol
Patrick Krol
Tahoe Chimney & Fireplace · NFI · CSIA · HeatShield Cerfractory Certified
CSL #949777 · NV Lic. #0084665 · P.O. Box 9526, Truckee, CA 96162
530-414-7600 · patrick@tahoestoves.com

Photos are from real Tahoe-area inspections. This page is general safety information, not medical or legal advice.

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