Concentric vent extension

[hoosier inspector]

This install reduces the vent diameter and I was going to write it up. But then I wondered why would someone extend the vent? The install manual only addresses the intake clearance. Would the proximity of the old chimney have an effect? Did an installer misread the instructions for clearance? Thanks for any help.

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[Mark P]

No I don't see how it cold be right. It has to extend at least 12 above the roof line or past the expected snow load, so maybe they get a lot of snow and that is why it was extended. If you have the make and model of the furnace you could look it up. Below I have cut and pasted two sections from the instrustions to a Nordyne Concentric Vent Termination Kit for Condensing Furnaces

http://www.nordyne.com/Literature/7083660.pdf

NOTE: If assembly needs to be extended, the 2 pipes

supplied in the kit may be replaced by using the same

diameter, field supplied SDR-26 PVC (D2241) pipe.

Do not expand dimension "D" more than 60 inches

"Do not operate the furnace with rain cap removed.

Recirculation of combustion products

may occur, or water may accumulate inside

larger combustion air pipe and flow into the

burner enclosure. Failure to follow this warning

could result in product damage or improper

operation, personal injury or death."