Hvac experts

jbett98 · Jan 4, 2016

I've seen electrical wires run perpendicular through panned joists and some galvanized water lines, but never any waste lines. Are your waste lines the old cast iron type with the leaded seals?
When they covered up the basement ceiling, they probably didn't try to seal up the metal panning, so you might have a waste line leaking somewhere and you're pulling in the vapors trapped in the ceiling area.
You could try pouring some strong scented fluid down a drain line and see if the smell comes up through return duct.
Try the tub/shower first, then if no change of odors, flush the toilet, then kitchen sink, etc.
My wife was given some bath salts that are so sickly sweet smelling I won't let her use them because they make me ill and something like that shouldn't hurt your septic tank.
Also, your sewer tank might be leaking and fluids/vapors are coming through the basement wall.
One more thing, is your garage located septic tank vented somehow?

41Slinger · Jan 5, 2016

Natural gas furnaces if not burning clean and efficient will sometimes give off a rotten egg smell, (the odorant that is put into NG so you can smell it). This odorant isn't being burned completely and so there is some smell, sometimes even outside from the chimney, can happen to water heaters too. Call the gas co. and they'll send a service tech to check your burner for free. They won't repair it but they will check it for you. Good luck

Cogs · Jan 5, 2016

Good info here, Stomper, Filson, J13, jbett, 41 and jb11. All that stuff mentioned above are all part of your diagnostic challenge. And, all said so far has been good solid information you can count on as being creditable. It's all stuff we would have to check out if we were to come for a service call.

Another thing to verify is; Has there been any water in the basement that may have seeped into the furnace base or ducting base? Open the furnace and inspect the base part inside for water stains or standing water. Do you have AC? If so, the drain system for the AC could have overflowed inside the furnace, this past summer, and there could be old water just sitting in there finally turning ripe right about now. It can even get into the blower wheel housing (might be able to here it slosh around when the fan runs).

Now, if the furnace has been replaced with a 90% efficiency type, you could have a water leak inside during the winter months. The drain system on those is rather involved but do need to be cleared out at least once a year.

Also, do you get the smell out of the supply air ducts when the fan only runs? If so, it's most likely with in the ducting system. It could even be an air leak spot in the return route that could draw in an outside source of odor (outside the duct but close to the return air path).

Happy diagnosing! You now have 1 hour to find the source, fill out a work order, price the repair and get an approval from the boss. Good luck!