sewer smell in air duct

[creekside]

Why do I smell sewer in my air duct?

[Greg]

I would start pulling registers and use a mirror & flashlight to check the ducts. if all is secure, go down under and take a close look.

Greg

[Greg S]

You most likely have a sewer leak or backed up sewer line under your home. Your heating ducts are not sealed very tightly and as such when the furnace/air conditioner runs it is drawing some air from under your home into the house.

[Mark440]

Been there. Done this one.

Every time I came home I kept smelling "moldy stale water" when the AC would cycle. Crawled under and found a section of belly cloth that was drooped way down...and real tight. Slapped it with my hand..and it slapped back. Used a small screwdriver to pierce a tiny hole...and out came a solid stream of water.

Made note of the belly 'section' and then attached a utility blade to a long pole (from a push broom). Slit smack down the center (lengthways). Man did the water coming pouring out! I let it drain the whole day then went back and cross cut every 4 feet or so. Pulled all the insulation out ...and ....found the leak in the elbow fitting. For no bigger than the leak was...it had been spraying water out for a LONG time!

In any case, made the line repairs - but left the area open for a solid week to let it fully dry out. I had no damage to the floor as the leak was below the floor and I guess I cought it before it got too full. The 'give' in the belly cloth was a life saver!

The final piece was to re-stuff with new insulation and then seal it back up. I used a heavy duty tarp cut into 4 ft x 2 ft pieces. I used a glue from Home Depot that comes in a gallon can (brown and white label??) and believe me this stuff puts off some vapors that are definitely hallucinogenic! The trick to the glue is to use a paint brush to thinly coat the patch area AND coat the patch piece. Let 'em air dry 5-10 minutes then stick the two glued surfaces together. The bond is instantaneous. NOTE: you get one shot at this. Any rumples or creases are there to stay.

Work your way down the entire repair area - overlapping each section a few inches.

Two years later....all is holding up just fine. The patches have not separated in any way. And the smell is gone.