I have a power vented water heater. The PVC exhaust pipe runs up in to the ceiling then horizontally outside my house. This was installed by professionals, not DIY. The outlet at the back is perpendicular to the wall - in other words the "mouth" of the PVC pipe open directly to the wind. If I stand in my utility room and place my hand over the back of the power vent intake when the unit isn't running, I can feel a decent cold draft. The floor above where this exhaust piping goes is very cold too.

Am I right to suspect that the installers should have added an elbow and made the mouth of the exhaust pipe "point down"?

Would a further step be add some sort of device on the end to only open when there's exhaust pressure?

  • I am pretty sure there is supposed to be an anti-draft flap on the end of the vent or at some location. Feb 18, 2019 at 23:14
  • Jim in my area the flap dampers are not allowed in the intake or exhaust powered or not we do however use 90's pointing down in most cases.
    – Ed Beal
    Feb 19, 2019 at 0:40
  • @EdBeal do you add anything after the 90? like a short run of a few inches? or is the 90 enough to at least reduce the drafting? Feb 22, 2019 at 16:52

1 Answer 1


Yes terminating down is a code requirement. It'll be more problematic if it's windy for a few days and you can't get hot water because its pressure switch continually trips.

  • Is it worth insisting on a flap after it terminates down? Feb 18, 2019 at 23:46
  • No, you don't put a back draft flap. Just pointing down. You may still get some draft inside.
    – Joe Fala
    Feb 19, 2019 at 0:24
  • Thanks. If my house has negative pressure I can only imagine it will exacerbate the draft. Feb 19, 2019 at 1:29
  • I always install sealed combustion units. They run quietly and avoid any issues with draft. Especially these days when people have like 5 bathrooms and a gigantic kitchen exhaust hood. Houses are often much tighter now too and that makes the negative draft problem so much worse when all systems are running.
    – Joe Fala
    Feb 19, 2019 at 1:42
  • I bet! Do you happen to have any links or diagrams of 'correct' termination? I have a contractor here and he's kind of giving me the run around - I understand that the draft won't be eliminated, but what's on there now is something like a 15 degree elbow with no additional straight run after that; I thought a 90 degree plus maybe a few inches of straight PVC would at least help. Feb 22, 2019 at 15:36

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