Seattle Home Inspector's Blog


A problem that never found a solution

To continue in the spirit of how things would be different on my planet, let’s talk about B-vents.

Rusting b-ventThis particular issue with B-vents is something that is likely going to correct itself, all on its own, as we move more and more to high efficiency gas appliances.  The problem with B-vents that I am discussing today simply won’t exist tomorrow because the furnaces will no longer require this type of metal vent.

A very common defect I see with these pipes is corrosion of the top foot of the pipe at the termination above the roof.  This corrosion happens because the exhaust by-products are slightly acidic and it eventually attacks the galvanized pipe and sooner than later the pipe fails.

I have seen pipes with just a little bit of rust or corrosion, where the standard recommendation is to have the top section of the pipe replaced.  Since often this rusting coincides with the demise of the furnace, the recommendation might read more like having the vent replaced in the context of the furnace replacement.

On my planet the entire length of b-vent (assuming that b-vent is even allowed on my planet—perhaps 50 years ago it was) would be required to be replaced when the furnace is replaced.  In my experience the life of this pipe is not much longer than the life of the furnace and it only makes sense that it should be replaced at that time.

However, it rarely does get replaced and the new furnace simply carries on where the old furnace left off.failed b-vent

When this happens, the pipe can completely fail as can be seen in the picture on the right.

On my planet, the top section of this pipe—the pipe above the roof—has long been required to be transitioned to b-vent that has a stainless steel jacket on the outer surface instead of the traditional galvanized metal.  On planet earth, no manufacturer makes a stainless steel type b-vent that I am aware of. 

This seems like a perfect example of “a problem that never found a solution.”

I for one will be glad to see b-vents and their associated appliances relegated to the dust bin of history.


Charles Buell, Real Estate Inspections in Seattle

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Comment balloon 11 commentsCharles Buell • April 09 2014 01:18PM
A problem that never found a solution
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