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Question DetailsAsked on 1/27/2015

cement flue pipe adaptar in attic leaking NOT ROOF.

This may be a cement asbestos pipe but it is rectangular through the wall and then in the attic there is a big adapter like cap turns it to a round shape and then exists the roof. The leak is dripping water from the connection at which I noticed some water damage down stairs. I've googled images of flue pipes but not seen anything like this. Anyway not sure how the connection seals but I suspect that I need someone to come out and remove the piece and replace it with a sheet metal connector. I don't know, just wondering how much something like this will cost.

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1 Answer


If this pipe is fairly smooth and uniformly shaped, then likely is asbestos concrete pipe. If not uniformly shaped, could just be metal ducting sprayed with asbestos coating.

While I suppose it is possible that the water is from condensation in the furnace flue transition piece, running down and leaking out first joint, I would be a lot more inclined to think that it is due to a missing or rusted through flue cap (above the roof) if dripping down inside the transition piece; or a failed roof jack (the metal cone and rubber seal which goes over the flue at the roof and seals the flue interface (with rubber seal) and hole through the roof (with the metal cone acting as flashing).

I would say in either case, if the water is coming from the roof, that a roofer is probably your best bet. If it is condensation in the transition dripping out at the joint, then some metal duct seam sealer should take care of that location - roofers usually carry a tube with them - should be hot duct use rated even though high on the flue, NOT asphaltic roof flashing sealer, which can catch fire. Vehicle exhaust pipe sealer (the asphaltic cement type) for about $5 for a tube will also work - if leaking from seam you could do that part yourself, just pressing it hard into crack with finger.

Of course, don't just seal there and forget - because whether water is coming in from roof or condensation you will end up with furnace rust.

If water is only condensation (usually does not condense enough to cause water damage on lower level though, unless staying in duct all the way) then you have too cold an exhaust gas at that point, so water will probably find its way to the furnace and damage things there. Solution could be a smaller flue if it is oversized (possibly from an oil oil fired furnace), or insulation in the attic to keep the flue warmer all the way to the roof exit point.

Repair cost depends on what is wrong of course, but typically not over about $200 labor if a leak from the roof, plus $0-150 materials depending on how much is rusted out or missing up there. If a flue problem, then probably more in the $250-400 range if some flue needs replacing, I would guess.

Answered 5 years ago by LCD

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