There is a machine in my basement/crawl space that is making a loud hum. The sound is really loud and needs attention. It normally does not do this. The text on the pipe says "waste and vent only." If I had to guess I would say it went to one of two upstairs toilets but really have no idea. What am I looking at? Should I call a plumber? What could this be?

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  • 2
    Not your question, but as far as I recall, that installation does not meet standards if it's in your crawlspace/basement. Any piping in the living area should be under suction, not pressure, so the correct location for the fan is in the attic or outside the house.
    – Ecnerwal
    Commented Dec 9, 2023 at 3:28
  • 2
    You should check if the fan is loaded with dust or anything else that can add weight to the fan blades. When that happens, it vibrates, which makes a lot of noise. Perhaps it simply needs cleaning.
    – bobflux
    Commented Dec 10, 2023 at 10:12

1 Answer 1


That’s a fan. It’s part of a radon mitigation system. It sucks gasses from under your foundation and vents them above your roof line, so that cancer-causing radon gas doesn’t build up inside your house.

  • thanks. so I need to get a new fan?
    – Bernie2436
    Commented Dec 9, 2023 at 1:59
  • 8
    Most likely. They run 24/7/365 and eventually the bearings give out. These days you might want to invest is a radon monitor, as you can get decent ones for $100-$250 rather than $11,000 or so like the olden days. Provides a clue if it's working right, or ...not.
    – Ecnerwal
    Commented Dec 9, 2023 at 3:24
  • 5
    Great question and great answer, +1 to both from me. I have never seen anything like this before, never would have guessed it! I live in slab house territory though. Commented Dec 9, 2023 at 16:01

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