As a Seattle Home Inspector I see a lot of damaged B-vent pipe. (B-vent is the typical type of vent pipe used to vent mid-efficiency gas furnaces.) Usually the worst of this damage is limited to the portions of the pipe exposed above the roof. On a recent inspection I found some of the worst deterioration of b-vent that I have ever found. All of this deterioration was in the attic space of the home.
It is also pretty rare for the interior liner of this double-wall type pipe to actually corrode all the way through. But this pipe had at least one area where venting into the attic space was obvious as condensate was building up on the surface of another b-vent pipe that was running above it.
Nearly the entire run of this vent pipe was close to horizontal. There was about 16 feet of horizontal run of pipe in relation to approximately 8 feet of vertical run of pipe—-a combination not suitable for proper drafting of the exhaust gases.
You might ask how this could have ever been installed this way.
Simple—-form not following function.
In this case the “look” of the front side of the home was more important than the safe installation of the b-vent pipe (and thus more important than the safety of the home’s occupants). The vent could have gone straight up through the roof above the furnace without any horizontal run of pipe—but it would have been visible from the Front side of the home. When “aesthetics” rules over safety, there is something wrong with the aesthetic in my opinion.
Charles Buell, Seattle Home Inspector
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