View Full Version : 1950 home on slab, returns on floor

10-10-2009, 08:29 PM
Our home was built in 1950. It is on a slab, and the returns are in the floor, run through concrete ducts. Where the returns come together under the furnace, there is an about 8" drop. While my husband was putting a new filter in, (under the furnace) he noticed that this area is filled with water, but only about an inch or two. He used a wetvac to suck the water out, and slowly but surely, the water returned. It does not reach the return ducts, and they are dry, however, in looking at this area below the furnace more closely, this has been happening for a while, because there is a line where the water has been and never rises above. I guess that explains why in the past when the furnace turns on it smells musty. This smell is bad today though. Any ideas?

10-10-2009, 11:34 PM
Sounds like a low point in the system. Condensation is building up on all of the vertical runs or the duct work is pitched slightly so it all runs down to the bottom where the water is collecting. A small hole drilled where the water collects would drain the water out of the duct work, but you'd have to patch up all the holes and see if there are any other areas where water or condensation could occur.

Check the humidity levels in your house since the lack of a proper vapour barrier may be causing too much humidity. Especially with the weather getting colder and wetter, this is a good time to fix it now. You may have to replace some ducting if it is rusted out as well.

Peter Griffin
10-11-2009, 05:04 AM
I might worry about mold and airborne bacteria also. Is the bottom of the furnace all rusty?

10-11-2009, 08:00 AM
There are many ways the water could get in there. If it always stays at a certain level it could be a high water table, or that could be the point where there is a hole so the water cannot get any higher. You could have leaking plumbing or soaked ground after a rain. Without checking the ductwork and other inspections there is no way to diagnose your situation.