We recently had a VERY old central heating furnace replaced and I noticed that the HVAC installer added the following PVC pipe shortly before the inspector arrived:

PVC Pipe

The metal vents were already part of the original furnace. I'm confused on what the PVC pipe is for.

I don't think it's the condensation water escape - those are going out both sides of the house. So what is this for and why is a metal vent insufficient? Does this pertain to newer standards/codes?

  • 4
    To make your house look ugly?
    – DMoore
    Aug 19, 2013 at 17:58
  • @DMoore lol I know right? It doesn't make sense to me. The only thing I can think of would be stricter requirements on ventilation tubes... but still.... Good news is that it passed inspection. So as ugly as it is, at least it's code-compliant.
    – Mike B
    Aug 19, 2013 at 18:05
  • I know that it has to vent so I am guessing he couldn't do out the side for some reason - mine vents out right by my dryer. Was that your old vent or did he run that in another vent? It looks terrible. I wouldn't have let him do it. Also why is it pointing down? This is a good question.
    – DMoore
    Aug 19, 2013 at 18:08
  • 1
    It is probably pointing down to keep rain out. I don't have a HE furnace but I see many of my neighbors with similar sized PVC vents (pointing down) coming out of the side of the house just above ground level (because the furnace is in the basement).
    – auujay
    Aug 20, 2013 at 14:56

2 Answers 2


That pipe looks like an air intake.

All "direct vent" style appliances (high efficiency on-demand water heater, gas fireplace, etc.) have an isolated air intake and it is common to have it suck in air from outside the building so as not to force air infiltration through doors, windows, etc.

Indeed, that is ugly. Our fireplace and tankless water heater have something far more elegant: two intake/exhaust stacks

The stack on the left is a natural gas tankless water heater. The right is a direct vent natural gas fireplace insert.


Often vent pipes go downward if there is a chance something can go inside. Very common application when roof of the house located under oak trees when acorns can vent down and clog the system

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