Photo of tranite cement-asbestos material used for air ducts in a slab over a sewer pipe (C) Daniel Friedman and Conrad HVAC Duct Sewer Odors Diagnosis
How sewage or septic smells may originate in or be transported by building air conditioning & heating ducts

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Sewer or septic gases through conduit or ducts: this article describes the detection and repair for sewer or septic gases & smells that are traced to passage through electrical conduit, open piping, or HVAC duct systems.

We describe how odors may be traced back to electrical wiring, conduits, or panels & sub panels, and how people stop that odor passage.

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Septic & Sewer Gases & Odors from Ductwork

Photo of tranite cement-asbestos material used for air ducts in a slab over a sewer pipe (C) Daniel Friedman and ConradReader Question: Question: There is a Septic Tank Odor Coming from a Vent Under My Air Conditioner: Who do I Call?

I live in a condo on the second floor, of three floors. I often smell a septic tank type of odor coming from a vent under the air conditioner. When I opened the vent there is nothing but open space.

When I go into the bathroom and open the cabinet under the bathroom sink I could smell the same smell.

The bathroom sink and the air conditioner and vent share a common wall. They are next to each other only separated by a wall. I don't know who to call to help fix the problem. I'm not sure if it's a plumbing problem or if it is an air conditioning problem. HELP!!!! - N.A.

Reply: Air Conditioners Themselves Don't Produce Sewer Gas but They Might Move Gases and Smells Around in a Building

A competent onsite inspection by an expert usually finds additional clues that help accurately track down an odor or smell problem. That said, here are some things to consider:

Watch out: we warn in all sewer or septic gas odor articles that because sewer gas contains methane gas (CH4) there is a risk of an explosion hazard or even fatal asphyxiation.

Watch out: also sewer gases also probably contain hydrogen sulfide gas (H2S). In addition some writers opine that there are possible health hazards from sewer gas exposure, such as a bacterial infection of the sinuses (which can occur due to any sinus irritation).
See HYDROGEN SULFIDE GAS

Also see ODORS in AIR HANDLERS & DUCT WORK for other sources of HVAC air duct odors & smells & how these are tracked to their source & cured.

Question: Sewage ejector pump system causing sewage odor picked up by furnace air intake

I have a septic system. I also have an ejector sump pump and pit that receive drain water from my master bathroom sinks and bathtub. This water is ejected through a 2” check valve into a 4” drain that goes to the septic tank.

I also have 2 in the ground basement catch basins flush with the basement floor and hooked up in tandem. They receive ground water from around, and under the house. The water is discharged into a common 2” line to outside the house where it increases to 4” and runs under ground for a long distance to a holding area where it is discharged. All that goes through these lines is ground water, no septic.

I sometimes have a septic odor coming from these 2 tanks when the tanks are emptied. The odor is then picked up by my furnace intake air duct and distributed throughout the house, and the bathroom toilet water also has odor problems. We have been putting chlorine bleach into the sumps while they are stagnant and not in operation, and this has helped, but I was wondering if you have any ideas as to how to eliminate these odors? - T.B.

Reply:

TB something is very wrong, unpleasant and even potentially dangerous if your warm air heating system is picking up sewer gases. I'm guessing that you are referring to smells around the sewage ejector pump tanks, not any outdoor components.

I've inspected quite a few sewage ejector pump installations. Where sewage odors were present I usually find as the cause one of the following [of course there could be a different defect in any case]:

See details about sewage ejector pump inspection, diagnosis, repair and maintenance
at SEWAGE EJECTOR / GRINDER PUMPS

Question: rotten egg smell from bathrooms and HVAC air handler

We are currently renting a condo and we have only been here a month. We started smelling a rotten egg smell coming from the bathrooms and the air handler.

We had the Fire department come out and they did not take two steps and they could smell what we were smelling and immediately said that it was sewer gas. Now we have had the wax rings changed in all the bathrooms and we still are experiencing this smell. Are there any gas experts in Jacksonville, Fl. ? - Helpless in Jacksonville

Reply:

Helpless in Jacksonville:

Local home inspectors equipped with a TIF8800 combustible gas analyzer or industrial hygienists who have experience in residential plumbing problem solving can look at this, but frankly I'd start with an experienced plumber. Could be you have a venting problem, clogged drain, blocked plumbing vent, or even open pipe connections in the walls or ceilings.

Notify your landlord in orally and in writing of these problems immediately because there are potential health and worse, explosion hazards if it's really sewer gas.

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