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John Arnold
08-15-2009, 11:22 AM
Today I saw a high efficiency water heater that exhausts through pvc terminate at a back-draft damper outside. This can't be right, can it?
A.D. Miller
08-15-2009, 02:04 PM
JA: It is my understanding that ultra-efficient heaters use sealed-combustion technology so they cannot backdraft. The damper would then be moot, if not specifically disallowed.
John Arnold
08-15-2009, 02:09 PM
It's a Rheem power vent and I looked up the installations specs. While they don't say "no back draft damper", they don't show one as an option, either. Just the pipe with a supplied screen.
A.D. Miller
08-15-2009, 02:24 PM
JA: I cannot think of a reason why it would be prohibited, but I have also never seen this installation before.
neal lewis
08-15-2009, 03:05 PM
John, is it possible that the damper could freeze closed due to the moisture in the products of combustion? I've never seen one on high efficiency equipment.
John Arnold
08-15-2009, 03:37 PM
John, is it possible that the damper could freeze closed due to the moisture in the products of combustion? I've never seen one on high efficiency equipment.

I think that's possible, based on warnings about freezing in the installation specs.