1974 home, built-up slab. Uptake gas furnace/air handler.
Furnace sits upon a wood return plenum, return is located to the left in the wall. I lift out the filter and there is a clay pipe which appears to be an additional return duct. The pipe disappears under the slab. I could not find the other end (home was furnished so who knows?) I know in-slab ductwork is common in some areas, but not here.
Are there any concerns I should be aware of with the type of material and design?
Also, on a side note…the wood plenum had termites. Glad I pulled the filter.
My biggest concern is mold and ground water. Because of this, I recommend a sewer scope.
Good point, especially considering the type of material and age
Those in-slab ducts always have water in them somewhere. I recommend blocking them off and building an above slab duct to replace it. If it’s 50 years old there is all kind of crap in it. Liable to be rusted /broken open somewhere.
Thanks Bob, I appreciate it.
Recommend testing for radon with under slab return ducting. The ducting is under negative presure and any duct leaks will aggressively pull in soil gasses.
Yes, I’ve seen a couple here on small commercial buildings, but not the norm by any means.
The wood plenum is common though. I see joist bays used for ducting all the time in older homes.
Same here. Not a big fan of wood plenums. Prone to moisture problems in my area to include mold.
In fact, you can see moisture issues in my photo which likely promoted the termites.
Brian some of those old in slab ducts did have asbestos in them.
In slab ducts are always problematic.
Your duct appears to have a damper which would indicate to me that the duct was at some time used for make up air to the exterior of the conditioned area. In the 60’s and 70’s a lot of transite duct was installed which also contained asbestos typically not a big concern it was not friable unless cut into with a saw. I occasionally still get calls about ducts beneath the slab foundation which we have a lot of that type installed in Okla and with improper drainage around the foundation you will have water in the ducts.