4" duct exiting slab. Any ideas why?

I have not seen this before; an approximately 4" diameter passage into the slab. Photo into the opening revealed nothing that helped me figure out why it’s there. Can anyone clue me as to its purpose? It is not the dryer duct.

Possibly a down draft from kitchen or kitchen island?

What type of building is it coming out of?

Possibly a floor drain exit?.. (which aren’t allowed like that, around here, any more)

Does look like a drain of some kind

Is there a water heater or air handler in an interior closet? This could be a drain for condensate or for the TPR extension pipe.

All good guesses, but:

No downdraft vent
No floor drain that I saw (residence)
AC unit was in the attic. Primary drain to bathroom sink, secondary at soffit.

Hard to say without more info on the structure. Here are some thoughts. First it is quite large for most other uses and it does appear to be PVC.

  • If the house had/has a center open area (garden, patio, etc., open on top and surrounded on most or all sides by house) it might be a drain point for the gutters.
  • If the house had a center section that was a solarium and open soil planting area(s) it might have been some type of area drain collection discharge point (seen that).
  • A flat roof drain discharge point. Would not be surprising that the previous flat roof was built out to typical pitched roof due to previous issues or concerns.
  • If it was remodeled it might have been old floor drains and/or second floor laundry area floor drain or even an old range hood downdraft vent as previously pointed out.
  • Original construction “Oooops” with a waste line placed to high and then abandoned and not properly closed off.

Without looking at the house and its history it really would be hard to tell. Did you look at online permits if they were available to see if it provided any information? Can you tell us a little more about the house?

Radon mitigation?

It is a thought but radon is a non-issue in our area, and most of Texas. However there are still those around here testing for it and I expect selling useless mitigation systems (useless since radon is not an issue).

It could have been an under slab chase for the ac freon lines.

Good possibility.

This could be it. It was near the condenser unit.

Manny, thanks for the suggestions. The first three were not present at the house. Although remodel is possible, it was a small tract home and did not look like it had seen any new walls since it was built, although that’s impossible to say for sure. The walls of the pipe were very thin, so I doubt it was a drain line.