We built a house two years ago and have had this problem for most of that time. We have the smell of sewer gas coming up through our heat and AC vents. It does not come from any of the sinks, toilets or tubs. We check the crawl space and attic when we smell it, and never smell it there. It doesn't happen all the time. We can go 2 or 3 months with no odor, and then all of a sudden it's back. It never lasts more than a day or two, nor does it last all day. It happens in summer and winter, but of coarse we smell it more when the heat is on and the windows aren't open. We have had the furnace man here to check the furnace and he says everything is fine. We have been on the roof to check the vents and they seem to be venting properly. We have contacted our builder and he can't figure out what can be causing it either. We are at our wits end! IT STINKS!! We would appreciate any help.

Where is your A/C condensation discharge line attached to ? Check it out and let us know before we e-trouble-shoot you...

Milo, It's connected to the sewer line.

Linda: Can you describe how is it connected ? Meaning: is it connected directly into the sewer ? Is there a trap before it hits sewer ? Or is it connected at the sink drain above the trap via branch T ? Or does it go to the vent ? Please, be more descriptive.

Milo, It is connected directly to the sewer line, and it does have a trap.