In a new construction home, there's some plumbing that I'm not familiar with. It looked like a funnel drain to me. The builder described it as a "pressure release and condensation drain for the furnace and tankless water heater". What I find particularly odd is it looks like there's open space between the white pipe and the black funnel beneath it. Is this normal/appropriate?

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  • 1
    yes the gap is required. I don't know the name of the fitting.
    – Jasen
    Feb 13, 2020 at 6:17

1 Answer 1


It is a Tundish drain which allows the liquid to continue while preventing any reverse contamination through use of an air gap.

  • 2
    Also known as a "standpipe air gap" Feb 13, 2020 at 12:43
  • Are Tundish drains common in the USA?
    – Craig
    Feb 13, 2020 at 14:08
  • @Craig I don’t know as I am not there, but you have one...
    – Solar Mike
    Feb 13, 2020 at 14:31
  • Air gaps are more commonly implemented with floor drains. Most forced-air furnaces will have them nearby. Standpipes like that are common with clothes washing machines, but in that case no air gap is required (and would be messy). In any case, this is not an uncommon situation in one form or another.
    – isherwood
    Feb 13, 2020 at 22:11

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