Discolored PVC water heater vent

[mjr6550]

Within the past several months (or more?) someone posted on one of the HI forums regarding discolored vent pipe at a water heater or maybe it was a furnace/boiler. I searched a bit and could not find it. I saw the same condition yesterday. I did a little searching in the net and found a few references to this condition, usually along with failed joints. It does not seem to be a very common problem, but could be a deadly issue. I'm looking for any feedback regarding causes/frequency.

BTW, the vents extended vertically up through the roof. Maybe 25 feet long. The pipe was not discolored in the attic area. Both water heaters were replaced within the past year, so sections right at the water heaters may have been replaced. The original installation is 15 years old. The water heaters are in a restaurant and may get heavy use. I felt a vent pipe while running and it felt pretty warm, but I don't usually touch vents so I'm not sure how unusual this is. I did not measure the temperature.

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[Mike Lamb]

I posted something similar in the plumbing section a while back. Barry Adair posted this link on the subject: http://plumbingengineer.com/content/pvc ... flue-gases

[mjr6550]

Thanks Mike, that is what I was looking for. I had seen that link. Your condition was a bit different. I did rear that UV can turn PVC brown. Apparently they put titanium dioxide or something like that in the PVC to prevent this. In that case maybe the pipe was not manufactured properly and one side was exposed for a while.