Rotten egg smell; drain pipe in cold air return?

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Drdadr

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Homeowner here, on well and septic. We had an existing 1990s home majorly renovated. We get an intermittent sewer/rotten egg/boiled egg smell in different parts of the house. I’ve had the builder and plumbing contractor out multiple times, usually they can’t smell it.
- I did have a lot of iron and sulfur bacteria in well water but took care of this. The smell interestingly changed a bit to more of a boiled egg rather than rotten egg…
- There is a lift pump pit in the basement that wasn’t properly vented. Fixing that helped a bit but it still smells randomly on the first AND second floors.
- sometimes the smell comes through the vents when the fan is blowing.
- They said they checked the roof vent stack and everything was fine.
- I just noticed that some of the PVC waste pipes run through the cold air returns. Could this be a problem? Is it allowed?
- Could the septic system somehow be wafting smells back to the house?

I’ve even gone through the basement on a ladder and smelled every PVC waste pipe joint and it doesn’t smell like it does upstairs.

Any ideas? I’m probably going to get a second opinion from another plumber but just wondering what they would be looking for.
 

Reach4

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A peppermint test could tell you if the smell leaks from the drainage system. If the well was bringing in H2S, I would think you would smell that when you ran water. H2S can be produced in the WH. In that case expect the smell to be more when you use hot water.

If water, consider sanitizing your well and plumbing. https://terrylove.com/forums/index....izing-extra-attention-to-4-inch-casing.65845/ is my sanitizing write-up.

There is another type of sewage system test called a smoke test. In both cases, the peppermint oil in hot water or the smoke from a smoke generator goes into a vent on the roof. It is important that whoever pours the peppermint not come in side until you and your sniffer helpers are done. Children tend to have good noses.

Tracking smells is hard for humans. There should be a specialist dog IMO.
 

Drdadr

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Peppermint or smoke test sound like good next steps. I don’t think it is from the water. There was a definite sulfur smell from the faucets but that went away after 1) iron curtain and 2) removing anode rode from water heater. This is a different smell. I actually bought an H2S detector and never found anything even when I could smell it. I put it over the sump pit and it didn’t detect H2S.
 

Drdadr

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Can anyone tell me if it is acceptable to have waste pipe running through cold air return? Yesterday the smell was very strong and it seemed to be primarily coming through the vents. When I go down to the basement it does not smell nearly as strong as through the vents.
 

John Gayewski

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Can anyone tell me if it is acceptable to have waste pipe running through cold air return? Yesterday the smell was very strong and it seemed to be primarily coming through the vents. When I go down to the basement it does not smell nearly as strong as through the vents.
No its not acceptable. It does happen and shouldn't cause a smell unless something else is wrong, but it's not acceptable.
 

Drdadr

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No its not acceptable. It does happen and shouldn't cause a smell unless something else is wrong, but it's not acceptable.
Thanks. I should have clarified is it “acceptable” versus is it technically legal per residential building code.
 

Drdadr

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So just to close the loop, are waste pipes within air returns a matter of local plumbing code? Or is there a straightforward answer? I’d just like to have an idea before I approach the builder again or get another plumber to inspect. The smell comes directly out of the vents when the fan is running which makes me more suspicious.
 

Jeff H Young

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So just to close the loop, are waste pipes within air returns a matter of local plumbing code? Or is there a straightforward answer? I’d just like to have an idea before I approach the builder again or get another plumber to inspect. The smell comes directly out of the vents when the fan is running which makes me more suspicious.
should the pipe be cast iron , galvinized , or copper I dont see a problem unless the joints are no hub. I wouldnt even look into it . plastic running through there I expect to be issue and would only concider if compliant but think its not.
 

John Gayewski

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So just to close the loop, are waste pipes within air returns a matter of local plumbing code? Or is there a straightforward answer? I’d just like to have an idea before I approach the builder again or get another plumber to inspect. The smell comes directly out of the vents when the fan is running which makes me more suspicious.
The only regulation against it would be in the nfpa, but that would just dictate that the material be metallic.

It's not proper but not illegal. It shouldn't cause an odor as the pipe is sealed. You should start looking elsewhere for the cause of the stink, unless the pipe has a hole in it.
 

Drdadr

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The only regulation against it would be in the nfpa, but that would just dictate that the material be metallic.

It's not proper but not illegal. It shouldn't cause an odor as the pipe is sealed. You should start looking elsewhere for the cause of the stink, unless the pipe has a hole in it.
The pipes are PVC. I would think if there are joints within the return ducts, even if sealed and not obviously leaking, the change in air temp and pressure may lead to breakdown of the seal and even the tiniest hole might draw out enough gas with the Bernoulli effect to smell up the duct system.
 

Jeff H Young

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I dont think your problem has anything to do with the type of piping you selected , you should have run cast iron or copper or even galvinized with durham fittings just like going through a fire rated wall. having joints in there isnt the issue. having broken pipe isnt good anywhere
 

John Gayewski

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The pipes are PVC. I would think if there are joints within the return ducts, even if sealed and not obviously leaking, the change in air temp and pressure may lead to breakdown of the seal and even the tiniest hole might draw out enough gas with the Bernoulli effect to smell up the duct system.
No
 

Jeff H Young

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Im not that sure how bad the plastic penetrating the return air is but I wouldnt concider it a technicality Id verify it im not up on fire codes id never run through a return air on my own without an ok from someone most likely the general or the inspector or at least hvac boss. if its wrong Id have them fix it . If I did that I could be forced to do rework and pay for the damages drywall paint , sheet metal.
 

Drdadr

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Im not that sure how bad the plastic penetrating the return air is but I wouldnt concider it a technicality Id verify it im not up on fire codes id never run through a return air on my own without an ok from someone most likely the general or the inspector or at least hvac boss. if its wrong Id have them fix it . If I did that I could be forced to do rework and pay for the damages drywall paint , sheet metal.
I was told by the builder and plumbing contractor when they came back out, that this is common in open floor plan homes and not against code.

I did a couple more tests on my own. Since I couldn’t do a proper peppermint test through the vent stack, I poured a bottle in an upstairs toilet and flushed it with my HVAC fan running. I then got a peppermint smell directly from the vents a couple minutes later. Of course I couldn’t reproduce it as strong when the builder came out!

Then I ran the attic vent fan at the same time as the HVAC fan and it makes the sewer smell come out, so it has to be drawing from somewhere. They couldn’t find any loose pipes in the basement. It has to be drawing fumes in from somewhere, but where?
 

WorthFlorida

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Do you have A condensation drain for AC? If so where does it drain too? If you do have AC, there should be a trap just outside of the connection to the coil drain. If dry, it can pull in air from the condensate if the drain is connected to the septic system. It should be an airgap if it is.

Another is if you have AC, the coils and drain pan can get nasty with mold. Remove the air handler door and check the drain pan. in no fashion can a sold pvc pipe with no cracks or leaks can it affect your odor.

Is there a humidifier on the ductwork?

When you did the peppermint test, we're any windows open? You're creating negative pressure inside the home. It is possible the way the house sits in relation to the wind, placement of the roof vents near open windows can pull odor from the roof vent. Just a possibility.
 

Jeff H Young

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Do you have A condensation drain for AC? If so where does it drain too? If you do have AC, there should be a trap just outside of the connection to the coil drain. If dry, it can pull in air from the condensate if the drain is connected to the septic system. It should be an airgap if it is.

Another is if you have AC, the coils and drain pan can get nasty with mold. Remove the air handler door and check the drain pan. in no fashion can a sold pvc pipe with no cracks or leaks can it affect your odor.

Is there a humidifier on the ductwork?

When you did the peppermint test, we're any windows open? You're creating negative pressure inside the home. It is possible the way the house sits in relation to the wind, placement of the roof vents near open windows can pull odor from the roof vent. Just a possibility.
If a Condensate connects to the DWV system it needs to be connected to a trapped line it cant just tie into a drain line or vent pipe. regardless of it has a trap on the condensate line at the a/c .
 

GL77

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Tracking smells is hard for humans. There should be a specialist dog IMO.
That's a great idea. If someone could train a dog, they could make a great YouTube channel of their jobs, people would love to watch that.

I was having an issue myself with what seemed like a sewage smell this past summer, albeit it was outside the house, right outside the bathroom which is where the main drain leaves the house. I was checking all of the plumbing and finally realized it was a leak coming from the nearby gas meter, had to have the gas company out to repair it. I sometimes wonder if people having these smell issues consider that natural gas has a similar rotten egg smell, never hurts to check.
 

Drdadr

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That's a great idea. If someone could train a dog, they could make a great YouTube channel of their jobs, people would love to watch that.

I was having an issue myself with what seemed like a sewage smell this past summer, albeit it was outside the house, right outside the bathroom which is where the main drain leaves the house. I was checking all of the plumbing and finally realized it was a leak coming from the nearby gas meter, had to have the gas company out to repair it. I sometimes wonder if people having these smell issues consider that natural gas has a similar rotten egg smell, never hurts to check.
My builder mentioned that. Actually I did have a leaky gas meter but that was fixed several months ago and thus not the source of the smell. I think the next step is smoke test and/or scoping the main drain.

Don’t know why it is intermittent. It’s not every time the blower runs but many times. It may be stronger after there are multiple showers at once. But then last night it came back after we hadn’t been using the water much.

Still can’t explain why the peppermint in the toilet was super strong the first time I tried it (all the way in the other side of the house) and then didn’t come through when the builder was there.
 

Drdadr

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Update: okay, so we had another plumber do a smoke test and immediately found a stub of a drain pipe from a no longer existing bathroom, sitting OPEN in a very tight hidden spot just above the furnace air intake between 2 joists. So intermittently the gases would escape and because of the location, they would get pulled into the HVAC system and pumped around the house. Problem solved. I still don’t like the drain pipes being inside the return air ducts but I guess they weren’t causing the problem.
 
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