Foundation w/return air ducting through slab?

Looked at a house yesterday built about 1950, single story, that ‘looked’ like a concrete foundation. Sides of foundation looked good, no cracking visible, etc.
On the interior, the hardwood flooring squeaked. Walking over it, could feel firmer/softer places. Able to see 1x4 t&g subfloor in mechanical closet and at doorway into kitchen (vinyl flooring).
One return air duct was located in entry hall near center of house, but in examination, the ducting traveled down appx. 2’ below floor level and turned toward end of house where furnace was located. Looked into attic thinking they traveled the duct up in wall cavity, but did not find any evidence in attic.

I guess the bottom question is 1) could this be a full slab foundation, but the flooring was installed over ‘sleepers’, or 2) perimeter pier with no venting ?

Anyone seen return ducting like this before? :roll:


Linda, I have seen air return ductwork in the slab in my area. It’s not very common though. I have not seen this installation in any other type of foundation but on grade slab. Tab

I have seen many slab on grade homes with asbestos transite pipe used for supply and return ducts. This was only determined during the demolition of the home.

Seems unusual that sheet metal ductwork would be run below a grade slab (if you are sure about that) … but I guess it’s possible.

I once inspected an older house that had no visible access hatch or venting, so I thought it was a slab-on-grade foundation. However, from the center of rooms I noticed flex in the structure when I bounced on the floor (more than could be from sleepers). Turns out it was a crawl space accessed from a floor hatch in the living room under a throw rug.

So I guess it could be either a slab-on-grade, or unvented crawl space without obvious access.

Thanks, folks.

The return was at baseboard level, and I know that sitting in the floor, my arm wasn’t long enough to hold the camera down in the vertical duct and shoot a pic into the horizontal duct.

Still not sure what it really was !

:o Thats what is great about this business you will not live long enough to see it all. I gave up years ago trying to figure out why people do the things that they do to a home.

A couple of years ago I had an inspection on a slab on grade foundation. My walk around revealed no foundation vents and I had already been in the home and It was indeed a slab floor. Surprise When I got on the north side I see this excess nice little wood door that appeared to be a crawl hole entry the right size and all. I am scratching my head at this point 2+2 is not 4 as to what I am observing. Having the curious nature that I do the door has to come off. Lo and Beho here is the square constructed poured concrete return air chamber to the furnace with excess to the exterior of the home. This door could be removed and the thermostat fan switch turned to constant run and it would allow outside air to be drawn and circulated through out the home giving the same principle as an attic fan with the windows open. I did write this up simply because the wood door was not in very good condition allowing uncondition air to enter the return chamber even when in the heating and or cooling mode. So don’t ever say that you have seen it all. My hair is gray and I am still learning.

</IMG> Ok i inspected a house yesterday built in the 1967 in Fort Worth Texas and the return air was at the bottom of the wall in two locations with the system on the other end of the house! So you know what i did i took the grills off and found a Concrete like storm sewer pipe that runs under the foundaion. The house has a musty smell the buyer said. What would you say in your report about this?
Take a look at the photos

4220 Hartwood Dr 045.jpg
4220 Hartwood Dr 115.jpg

Robert Flaa TREC #9501

Whoa someone dug an old post of mine:cool::cool: your return air filter must have been at the furnace, duct coated with lint did it have the appearance of ever having water in the duct could not really tell from your pic. I would recommend having the ducts professionally cleaned and if there is any indication of past or present water marks I would recommend a camera scan

Ductwork run below grade has a great potential for moisture penetration and mold growth that is then blown throughout the house. They at least need regular maintenance and duct cleaning.