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Sweeping a fireplace chimney


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It wouldn't be prudent to ever suggest that one scenario requires less inspection. I've found damaged or loose connections between sections of metal flues in pre-fab fireplaces. While I can't offer any scientifically based information, my experience over 16 years as an inspector and 15 years as a mason, has been that the triple-walled metal flue pipes tend to stay cleaner longer. I believe this is due to being round, which is the shape smoke tends to swirl up in, even in square and rectangular flues. The triple layers may also offer some insulating quality that permits the flue to stay warmer all the way to the top, which impedes condensation and creosote collection.

Masonry flues tend to be over sized, due to the fact that they are square or rectangular, which permits them to cool down faster. That in turn can permit excessive condensation and creosote collection. I've seen flues that were practically blocked by the honeycomb collection of creosote and soot. But, before they get to that point, all the corners will fill first leaving that relatively round path through the length of the flue.

In the 80's, at the request of Dr. Brown of University of Texas' Pyrotechnical Department, I constructed a unique masonry chimney to be used with a wood stove (the study was really based somehow around false advertising, don't ask me how this fit in. I had originally called to bounce a theory off someone in the department and, hence by the end of the discussion, I was helping them out.): It was constructed of an 8" thimble and transitioned to 8" round flue sections, which were not easy to come by at the time. In other words, the aim was to keep the volume of the flue the same from the moment smoke left the appliance until it was released to the air. Round, as mentioned above, is the perfect path for smoke. A large cavity was left around the flue which was filled to the top with Perlite (good to 2000 degrees) as an insulator. I was asked to return to and inspect the flue for several years. For as many years as I inspected it, cleaning was never necessary. Every year it was as clean as whistle, which nails down flue cooling and condensation / creosote collection. If anything, it worked a bit too good as some creosote would leach out of joints near the bottom looking a bit like used motor oil stains in the masonry.

So, to answer your question, I think the wise response is to say that every flue that is routinely used should be routinely inspected, but masonry flues will tend to experience higher creosote collection and deterioration.

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While, I can't offer any scientific based information, my experience over 16 years as an inspector and 15 years as a mason, has been that the triple-walled metal flue pipes tend to stay cleaner longer.

Thanks, Michael; that's some useful info.

Is a dirty metal flue pipe any less dangerous/less a concern than a similarly dirty masonry flue pipe?

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While, I can't offer any scientific based information, my experience over 16 years as an inspector and 15 years as a mason, has been that the triple-walled metal flue pipes tend to stay cleaner longer.

Thanks, Michael; that's some useful info.

Is a dirty metal flue pipe any less dangerous/less a concern than a similarly dirty masonry flue pipe?

Not in my opinion. Creoste collection is flammable and once it's ignited it sounds like the space shuttle is lifting off. I've experienced it. I lived in two 100 year old homes with only wood heat. A chimney fire will scare the crap out of you. The flames are so intense and the demand for oxygen so fierce that the chimney will actually shudder from the vacuum. That's the effect that sounds like the Space Shuttle taking off and I guarantee you it will get your full attention. I was sweating bullets. Fortunately, I had a good wood stove with proper gaskets and was able to shut the stove down and starve the flue fire until the fire department could arrive. A 100 year old log cabin would have gone up pretty darn quick.

Flues don't catch fire, creosote does and as I said, it's BAD news.

Masonry flues don't usually crack from the fire, but rather from the abrupt change in temperature when they are improperly (quickly) extinguished - like plunging hot glass into cold water. However, I suppose that a stone cold masonry chimney with a ton of creosote in it that catches fire, can just as easily crack.

As a matter of fact, should you ever see a chimney with an ominous redish orange glow in the smoke coming out of it and sparks spitting up out of the flue, you're witnessing a chimney fire. The glow is because the entire inner surface of the flue is on fire. I actually stopped to tell some folks that their chimney was on fire, and it was. We waited together for the fire department to arrive.

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It was used extensively, I lived in the country then and was planning to build the chimney for a neighbor (rural definition - same town) and when the request came in, I bounced it off of the fellow, who consented. Back then we were all tradesman and farm hands who worked a whole lot less during the winter and were consequently cash-poor each winter. Wood was free and fallen down everywhere for the taking. So, we all cut, split by hand and burned wood 24/7 all winter. His chimney was worked hard. That's why, in his case, the creosote actually would run down the flue and leach out when he burned too much green wood. His wood stove was in the cellar and heated the entire home.

I had a friend that was a member of the basketball team that I played on and sponsored, back then. He owned a huge hog farm and had constructed collection tanks for the waste under and near the pens for conversion to methane. The project was in the infancy stages and I'm betting he was getting huge help from the government in the way of incentives. He was also a whiz with a welder and constructed from scratch impressive "papa bear", we called them, wood stoves out of plate steel. He would incorporate tubes through the upper chamber of the stove to add a blower to the stove. They were impressive.

My chimney customer was burning one of these "papa bear" stoves.

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Creoste collection is flammable and once it's ignited it sounds like the space shuttle is lifting off. I've experienced it. A chimney fire will scare the crap out of you. The flames are so intense and the demand for oxygen so fierce that the chimney will actually shudder from the vacuum. That's the effect that sounds like the Space Shuttle taking off and I guarantee you it will get your full attention. I was sweating bullets.

Ditto, not an experience you want to repeat. Mine was set up so that I could see the inner pipe of the triple wall while it glowed bright red while vibrating.[:-bigeyes

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Creoste collection is flammable and once it's ignited it sounds like the space shuttle is lifting off. I've experienced it. A chimney fire will scare the crap out of you. The flames are so intense and the demand for oxygen so fierce that the chimney will actually shudder from the vacuum. That's the effect that sounds like the Space Shuttle taking off and I guarantee you it will get your full attention. I was sweating bullets.

Ditto, not an experience you want to repeat. Mine was set up so that I could see the inner pipe of the triple wall while it glowed bright red while vibrating.[:-bigeyes

Well, I'm glad I was in my shoes instead of yours, Jim. In my case, it was rather like that vibrating sensation you experience when you're driving down the road and open the right windows to the right amount to get that vibration going in the car, but masonry won't give. In your case, that red weakened metal was being stressed to the max - working overtime. I bet if you could somehow document the stress on the metal experienced by the vibration during that peak demand for oxygen, it would be pretty shocking.

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