I'm installing a utility sink and the only place to put the plumbing (if it's going to be right under the sink) is either directly behind or infront of this vent... Is there any reason not to put it within inches of the duct vent?
The sink will be on legs so it's not going to block the duct.

That's where it's going

that's under the house in the crawlspace

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    – FreeMan
    Commented Aug 20, 2020 at 16:02
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2 Answers 2


In my experience, there are at least two things you should be aware of.

  1. Running hot and cold water lines will cause the water temperature in the lines to change a lot quicker than ambient. The actual distance of the run and distance between pipe and duct will affect the effect. When my air conditioner is running, the hot water gets cold within 15 minutes since it's last use and then requires running the water for an extra minute or two to clear the lines. The opposite is true for the could water when the heater is run. This is really only a minor inconvenience, but a moderate inefficiency.

  2. A floor vent in a room with running water will eventually flood, even if it's only a small spill or leak. The water will run through the vent and eventually come out in an inconvenient and unexpected location. The moist duct will collect lint, then mildew or mold and will be a pain to get clean.

Because of point 2, I would strongly recommend raising the duct and vent at least an inch proud of the floor around it.

  • Thanks, i appreciate your advice. #2 does sound bad. #1 probably an acceptable outcome. Any suggestions on how to raise the vent?
    – Sarah
    Commented Oct 5, 2018 at 14:53
  • I'm not sure of you're technical ability, be what I'd done was get a short 4" sheet of duct metal a little wider than the diameter of the duct and bent it to fit tight around the existing duct work. Make sure the flange is on the outside of the duct to keep water out. Secure with duct tape.
    – psaxton
    Commented Oct 6, 2018 at 0:27
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    Re: #1, I have a bathroom with a cold water line running next to a heat duct. The cold water is often around 100 degrees when I first turn it on. As well as being inconvenient, it's a waste of energy. At least insulate the pipes in that area.
    – isherwood
    Commented Nov 13, 2018 at 15:15

The only problem I can think of is if the sink over flows, in cold areas I have seen vents under kitchen and bathroom sinks to help prevent the pipes from freezing.

  • That makes sense. If water gets into the duct how bad is that?
    – Sarah
    Commented Oct 4, 2018 at 19:24

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