As for why it never happened before, I can't say but the HVAC guys had to work on the double walled pipe when we did the roof because it kept coming apart. Maybe the pipe had come apart before and the spent gases where being eliminated in several places. Those guys say the pipes are fine but we know better.
The local municipal building official agrees with me that the double walled pipe should, by code, pass through the roof line for two feet past the nearest obstruction or roofing within four feet. As the roof has a 12/12 pitch, a twelve foot rise in twelve feet, the roofing four feet away is four feet higher. If the pipe is not near the ridge, adding two feet to the altitude of the furnace flue should mean that the piping terminates six feet above the point of exit.
The by-product of burning natural gas is water and heat, or water vapor, and carbon monoxide. Carbon mono-what! The fact that the pipe does not extend past the roof line but only into a vent means that the pipe does not have the proper type B gas cap on it also. But I am ashamed to admit, but only a little because I now know, that if the pipe angles too much or is too large, the water vapor might condense before it extracts itself out the top of the pipe.
This makes perfect sense but I never considered the math behind the pipe. I knew there was some but just like most people consider dentistry and exact science, I assumed that licensed HVAC people knew the simple rules. Now I must master the nuances of furnace and hot water boiler repairmen because they are effecting my business.
And they might kill my customers and leave me with a manslaughter charge or two to deal with. At 53 years of age I'm not ready to take on a life of crime. I'll leave that to the experts. My line of work is protecting your home and health. Read previous blogs.
The pipes in this scenario also fell easily when touched. How secure could they have been. When the pipes are perfectly vertical they sometimes have no strapping. They should. Something to keep the things that go bump in the night, in the attic, from knocking them loose and causing a lot of clanging and bashing from going on.
When the pipes are angled and are fit together with adjustable elbows, they should be strapped at each end. The seams of the joints should also be sealed with the silver HVAC tape that resists the high heat.
Once, when I was scaling a steep roof, I reached for a 3" double wall pipe, usually for a hot water heater because 5" and larger are for furnaces, and intended to only use it for a little help. Before I felt a thing I heard the hiss and searing of flesh somewhat reminiscent of an old locomotive engine. I knew what this meant for me in the upcoming weeks.
Skip the crying and go directly to yell. Do not collect $200.00. Burns get worse before they get better.
Back at the gas farm, the science of furnace flues has become clearer to me. I knew that chimneys had to be two feet higher than any part of the roof within ten feet of the chimney and I now know that gas flues need to be two feet higher than roofing or obstructions within four feet. That is the word of the Southlake inspector.
When asked if we could change the flashing and add a double walled extension to short pipes, he reluctantly said yes. you could tell he didn't want us there but he gave me special dispensation after listening to my chants.
If you missed it, the condensation usually reveals itself in colder and more humid environs. Next time we have those, run to the attic and see if you have attic drip. The headache you save might be your wife's, a carbon monoxide pain.
Jon Alan Wright
Jon Wright Roofing, Siding, and Windows
1915 Peters Rd., Suite 310
Irving, TX 75061
972.251.1818 Office
214.718.3748 Cell
972.554.8090 Fax
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