Large diameter pipe in utility closet.

The home was a townhouse on a slab built in 1993. 2 story home

Downflow furnace. In slab ducts.

What is the large diameter pipe for in the closet? Return is above, supply is in the slab. No fresh air intake but it had louvered doors. Would this be the supply for the 2nd floor. Seems oversized.

There were also some flex pipes in the garage attic and I could not tell were this one pictured terminated.

You probably do not have enough info from the pics but I was not sure the purpose of the large diameter pipe.

I did make a note of the condensate pipe that was loose/leaked and had a lot of elbows.

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Yeah pics are tough to make out - could be for make up air.


If this down flow furnace was supplying conditioned air through the slab, then that duct must be the supply to the upper floor. Did you run it and then shut it down to test the upper floor supplies or even feel the duct itself when the furnace was in operation?

The guy who installed that condensate piping was definitely on some hard drugs…


I felt the pipe but did not feel any warm temperature. I did verify heat up stairs. The furncace was not operating properly as it took over 10 minutes for the glow igniter and burners to kick on.

Agree that drugs or glue was used when installing condensate.

Looks like a 10 inch PVC sticking out of the slab then converts to 12 inch metal and would have to be the upstairs supply air how many drops are up stairs.

3 bedrooms and 1 bath. 4 drops.


That duct has to be a supply for the upper floor. I can’t see it being used for anything else. If this wasn’t hot to touch, did you check the degrees on the upper floor supplies?

I was getting about 98 degrees at the 2nd floor.

I did not understand the set up in the garage attic. One looked like it terminated at the ceiling. Could not get over there due to storage and ameture insulation.

I did figure the large pipe to be 2nd floor supply. Just had a brain fart at the inspection.

Thanks for the assistance.