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Unknown Sources of Noxious Gases

Sufferer | Posted in General Questions on

Looking for some expert advice here on a long tale of woe- since moving back to our house after a renovation we have been getting sick with severe throat and chest irritation and other odd symptoms. We’ll move out for a while, fix this and that based on some research or recommendations, and then come back and have the same symptoms start all over.

After trying numerous air testing companies, we finally received a report that nitrogen dioxide, sulfur dioxide, and hydrogen sulfide (correction: it was ammonia, not hydrogen sulfide) were spiking in random parts of the house with no perceivable pattern and no obvious relationship among the three gases (they were coming up in different rooms at different times). The only pattern of note was that all three were correlated with higher relative humidity readings. We checked the connections on all the gas burning units in the house and have not found anything that seems to be leaking.

I would appreciate any answers or tips.

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  1. plumb_bob | | #1

    Attached garage with vehicles running? Vehicles idling in driveway close to air supply inlets?

    Hope you figure this out soon.

    1. Sufferer | | #2

      Thank you :)
      No we don’t have any vehicles there

  2. Expert Member
    DCcontrarian | | #3

    Those sound like combustion products.

    1. Sufferer | | #5

      Yes, but we have not been able to locate the source. How else would you recommend we go about finding it?

  3. Expert Member


    What did your renovation entail? What new equipment was installed, what materials used?

    1. Sufferer | | #6

      Hi—reframed the roof in order to add a couple of bedrooms upstairs, put in new water heater and added a zone to an existing hvac system. Added a fire sprinkler system.

      1. Expert Member
        Michael Maines | | #13

        Did you add a vapor retarder in the basement? That has been known to result in odors like you're describing, on rare occasions. But the mechanical work is a more likely culprit.

  4. Expert Member
    BILL WICHERS | | #7

    The presence of sulfides makes me think you have a sewer leak somewhere. I wouldn't expect that from normal natural gas combustion appliances. I would check for any hidden damage to the drain and vent system for the home, since construction work can sometimes damage existing PVC drain and vent systems (drill a hole through a pipe by mistake, or crack/fracture a pipe from impact or stress). The easiest way to do that is probably to have a plumber run a camera through the drain and vent lines in the area of your renovation project and look for any signs of damage.


    1. Sufferer | | #8

      Hi Bill,

      I just looked at the data again and realize it was ammonia rather than H2S in the recent readings. I had confused it because we found smaller amounts of H2S in a previous test but mainly confined to the basement. Let me know if you still think it makes sense to check the drain and vent lines.

      1. Expert Member
        DCcontrarian | | #10

        Ammonia wouldn't be a combustion byproduct. It's definitely something that might be a sewer leak.

        I would definitely look at smoke testing. It seems like it's an intermittent problem, so if that finds nothing I'd see if your plumbing has any air admittance valves that might be intermittently leaking. Another thing you see sometimes is a plumbing vent that leaks when the wind outside is blowing in just the right direction.

        A plumbing leak would also explain why the elevated levels are associated with higher humidity readings -- the leaking vent is bringing humidity into the house.

        1. Sufferer | | #11

          Who would be the best type of person to call for this kind of thing? I have tried working with some of the local plumbing/sewer companies but they don’t seem to understand the issue.

          1. Expert Member
            BILL WICHERS | | #12

            Plumbers should understand venting -- it's part of their code! Maybe try one of the plumbers the specializes in plumbing problems, such as the crews that can snake out sewer lines (not just clogged drains).

            BTW, I like the idea of smoke testing. That's probably a better option than running a camera through all the lines in this case.


          2. Expert Member
            DCcontrarian | | #14

            You want to find someone who does smoke testing. Maybe ask at a local plumbing supply house? Go when they're not busy, like after lunch and ask at the counter.

            An alternative is to find a distributor of the smoke equipment and see if they can tell you who in your neighborhood buys the smoke bombs.

        2. Sufferer | | #15

          What I’m hearing is that the smoke test wouldn’t work because the walls are already closed. Does that make sense? They want to start opening walls instead to find the source of the leak directly.

          1. Expert Member
            DCcontrarian | | #16

            Maybe. If sewer gas is coming into the house, smoke could follow the same pathway. But it could be too diffuse to detect. But I don't see how ripping out drywall willy-nilly is a practical alternative.

          2. Expert Member
            BILL WICHERS | | #17

            Find out if their smoke rises to the ceiling or falls to the floor. Now you can use a hole saw to open tops or bottoms of wall cavities in the areas of drain pipes until you find a place where smoke comes out the hole. Once you know which wall cavity the problem is in, you can open up only that part of the wall. The relatively neat and clean hole saw holes will be easy to patch. I would suggest about a 2” hole saw for this.


  5. walta100 | | #9

    You may want to have your drain piped tested with smoke.

    They fill the pipes with smoke and use the pressure from a fan to push the smoke out any leaks.

    Take a look at this video


  6. Sufferer | | #18

    So an update here: we ran smoke through as suggested and found it coming out in one spot on the top floor inside of a closet that holds an hvac unit.

    Inside that closet there appears to be a pipe that’s open and connected to a bathtub in an adjacent bathroom. So it’s disconnected from the vent and presumably leaking gases into the house. Potentially only a small amount as there’s a p trap on the tub in question. I have no idea if there are other pipes that could also be leaking into that area.

    My question is can one pipe deep inside of an unused hvac closet have been the thing causing all this trouble? Maybe the gas was somehow getting into the ducts and through the house? Or is this more likely just the tip of the iceberg and we need to keep looking?

    1. Expert Member
      BILL WICHERS | | #19

      If that pipe is on the side of the trap opposite from the connection to the tub, then that pipe is open to the sewer and can vent gasses. I wouldn’t be surprised if the HVAC unit was drawing stink out of that pipe, but since it looks like that pipe is left over from a demo job, I’d keep checking to see if there were any other that were missed.


      1. Sufferer | | #21

        Left over from a demo job! I wish!
        No this is how they left the house looking after a renovation. I also found an empty box of parliaments and a McDonald’s drink in there… from two years ago.

        1. Expert Member
          DCcontrarian | | #23

          That's pretty normal. It wouldn't be unusual to find booze bottles.

          1. Expert Member
            Michael Maines | | #27

            I've done a lot of renovations--I'd say it's unusual to NOT find booze bottles!

    2. Expert Member
      DCcontrarian | | #20

      I think that's your problem.

      1. Sufferer | | #22

        And with that pipe venting stink in there for two years, is there concern for long term contamination. For example, would the foam insulation in there or other materials have absorbed the fumes and continue to give off gases? Or once the pipe is fixed will it all ventilate out?

        1. Expert Member
          DCcontrarian | | #24

          I think capping the pipe will solve your problem.

        2. Expert Member
          BILL WICHERS | | #29

          I doubt anything would have absorbed any of the nasty stuff. If you had *liquid* coming out of the pipe, then I'd be more concerned. With only what is likely to be pretty low concentrations of foul gasses, you probably won't have any issues aside from maybe needing a week or two (and that's probably on the high side) of time for things to air out and get back to normal.

          I agree that capping that pipe will probably solve your problem, assuming it's the only open pipe. Do check that it's not a vent pipe for something though -- if it is supposed to be an active vent, then you need to extend it to the outdoors so it can function, or see if an AAV might work for whatever the vent is venting, in which case you could replace the vent pipe with the AAV.


  7. walta100 | | #25

    Capping off does not sound like a code approved fix.

    It sounds to me like the smoke has you looking in the right location but you have not yet located the fault.

    You are looking for a hole in a pipe or a separated glue joint maybe a failed air admittance valve.

    I have to ask were permits pulled for the remodel?

    Did a licensed plumber do the work?

    After this leak is fixed, I would want another smoke test.


  8. Sufferer | | #26

    Where is that pipe meant to be going? Out through the roof?

    It’s sitting in an attic crawlspace. I’m assuming they didn’t finish whatever the intended work was. It’s close enough to the roof that maybe it’s meant to be vented through - or capped - or what else could it be?

    I have no idea how this passed inspection.

    1. Expert Member
      DCcontrarian | | #28

      If it's still an active vent it needs to go through the roof, or perhaps be connected to an air admittance valve. It's very usual to join all the vents in the attic so there's just one hole through the roof. If it was made obsolete by renovations it could just be capped.

      >I have no idea how this passed inspection.
      In every human endeavor half the people are below average.

      1. Expert Member
        BILL WICHERS | | #30

        I have found inspectors to miss a great many things. Sometimes people have even died as a result of structural problems that get missed, but luckily that is a pretty rare occurance. It's much more likely for inspectors to miss simple things like a pipe fitting that didn't get glued, or an electrical connection that was not tight. There are probably bazillions of such minor issues out there that go unnoticed since they aren't severe enough to actually lead to problems.

        The thing that always concerns me is that when a project is freshly done in a commercial building, there are a LOT of "fire stop" requirements that need to be met. These are all related to keeping the integrity of fire barriers to slow the spread of a fire if there ever is one, to gain time for people to get out safely. Every project afterwards tends to skip that step, sometimes as badly as smashing a hole through a fire barrier with a hammer and running small wire through it. No one ever notices, but if there's a fire someday...


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