Sewer Gas Smell Eliminated!
Posted by Paul and Cindy Hartwell on June 13, 1998 at 13:47:19:
In March of this year we posted a question about a sewer gas smell we were getting in two heating/cooling vents (out of 8 total) in our 1950's built slab rambler. We had many responses to our problem and although there were good suggestions none worked. We finally did diagnose and correct the cause of the smell so thought others would be interested in case the same happens to them.

As backgound, we have a downblowing system where hot/cool air travels in concrete air ducts underground and then discharges through vertical vents in the base of walls in the rooms. All the plumbing is also underground and everything is beneath the concrete slab so it is incredibly hard to know what's going on.

Some of the previous suggestions/remidies were :-

- broken/leaky drainage pipe (UNLIKELY - we "snaked" the 2 suspect air ducts and they were dust dry!)
- have a camera survey of the drain pipes done (COULDN'T! - we called one of the largest plumbers in the area and our pipes were too narrow for their camera to get down)
- abandon the underground duct/vent system and put a new furnace/a-c and duct system in the attic (WOULDN'T! - hugely expensive and we also once rented a house with ceiling mounted vents and hated them; also the contractor could not guarantee the smell would be eliminated)

In the end the solution was obvious when we exposed it.

By word of mouth we found a neighbor who was a heating/a-c contractor who knew these systems real well. He suggested we uninstall the furnace and a-c unit to get at the "pit" beneath it and the open ends of the air ducts leading from it. This was relatively inexpensive for 2 days of labor ($520) compared to the $1000's we had been quoted for other "solutions". We said go ahead.

And what we found under the furnace was a shock! Instead of a nice brick/concrete pit we found an open hole with the air duct pipes just lying in dirt and gravel. So immediately we knew we were wasting half of our air which was going outside of the pipes and underneath the slab. The thought was also that this "loose" air was picking up random sewer gas smell and then entering back into the air ducts further down.

So we spent a weekend building a brick and mortar pit which was complelely closed except for the opening under the furnace/a-c and the ends of the air duct pipes - not a job I'd recommend working on knees and stomach for 10 hours mostly upside down!

Anyway, Monday the contractor came back in, reinstalled all the units, turned on the blower fan, we put our noses down by one of the "bad" vents smell....and a heck of a lot more air!! We were so pleased you'd have thought we'd won the lottery!!

Why, after some 40+ years the smell started last year we can't explain but we certainly CAN blame the original builder for real shoddy work.

We hope this (long) tale helps others in possibly similar situations -- I know this Web site was a great resource when we found it and hope we can contribute back.

Paul and Cindy Hartwell
Springfield, VA

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