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Flue corrosion


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I was at a house today that had masonry chimney, with a clay liner, and a metal liner (flexible metal type). The chimney was capped, and the oil fired furnace was installed about a year ago. The clean out cap at the base of the flue was corroded with a blueish green hard (not wet) substance and there was also a blue stain on the floor below (cap sealed). Also, there was evidence of prior leakage in the form of a white flaky substance at all flue joints and inside the furnace cabinet itself. What is this blue substance? And is this white flaky substance evidence of moisture intrusion or condensation? The flue looked as if it was recently installed (possibly with furnace). Thanks.

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Yep, single-walled connector into a masonry flue is allowing flue gases to cool too rapidly and the acid is reacting with the zinc in the galvanizing and causing that mess. Maybe replacing that single-walled connector with a double-walled connector will help; but, if they have one of those corrugated flue liners, I doubt it unless they've sealed the opening between the liner and the sides of the stack so cold air can't surround that liner inside the stack. Maybe the liner isn't properly sized.



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Reminds me of the time I did an inspection on a 1928-era home. The clay tile liner had a huge hole in it (as seen at the fireplace smoke chamber, where the flue liner passed-by).

Anyway, the client convinced the seller to 're-line' the flue (and isolate the flue from the fireplace smoke chamber).

Client wanted me to return to 'inspect the new flue' and I did. I opened the clean-out in the basement and looked up and took a photo as well. The metal liner had 'come apart' at the seams for a long distance during the process of installation.

I told them to 'call the guy back to replace it'.

He did. I returned. This time, it looked fine from the clean out. I then proceeded to the top of the chimney (via 2 LG ladders mind you... you had to have been there...) and lo.. the top of the flue liner was just kind of 'sitting there'... not terminated properly.

"Call the guy back to finish this properly'... (Photos taken, etc).

4th trip back, I go back up to the chimney top and see a textbook super-fine job had been done. Classic.

And on the side of the crown, was the poor chimney guy's cell phone...

I brought it down and called his voice mail...

Morale of the story is that you can never assume anything and that when you see that a chimney has been 'relined', don't be surprised if the metal liner is totally wronched-up inside and that can lead to draft issues like this as well..

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