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flue gas?

ryanwc Member Posts: 50
We had some remodeling done in our basement a year ago, including putting up a new internal wall.

After the remodeling, we sometimes smell something in the area around the two heating units. We have a gas boiler with hot water heat and a gas hot water heater. The boiler is a condensing unit with (I think this is the right term) a sealed combustion air supply and vent -- in other words, unless there's a break in the vent pipe, no exhaust gases could possibly be coming from this unit. The water heater is standard - with exhaust gases hot enough to drive them up the chimney, assuming there isn't negative pressure causing a backdraft.

The remodeler assured me that after the new wall was built, the resulting space around our boiler area would still be sufficient to allow exhaust gas to flow out, and based on what I read, he's right. The boiler & storage room is about 12 x 25.

Last week, I bought a Temtop air quality monitor. It seems to show the air around the two heating units is good. It measures HCHO (formaldehyde), PM 2.5 (fine particulate matter), TVOC (volatile organic compounds) and "Air Quality Index" (I'm not positive).

If there were exhaust gas leaking back in because of a depressurizing situation, would any of the gas fall into the categories this monitor is measuring, or did I get the wrong monitor to know what's going on?


  • kcopp
    kcopp Member Posts: 4,448
    If the water heater is Atmospheric (chimney vented) it is possible that you could be getting spillage. If the house gets negative pressure (Bath fan or vent hood turned on) it may not vent out.
  • Dave Carpentier
    Dave Carpentier Member Posts: 604
    A "low level" CO detector is best to check, and for your safety.
    A regular CO detector will work too, but they're slow to read and really only alarm once the CO nears the "get out of the house" levels. A low level one is better for detective work, and for noticing the lower level CO problems that can cause health concerns over longer periods of exposure.

    Has this smell been fairly steady since the remodel ?
    30+ yrs in telecom outside plant.
    Currently in building maintenance.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,157
    You may want to read this bulletin
    It may explain your situation

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    rick in Alaska
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    I thought @Jim Davis debunked the 'orphan' theory many times, and I doubt it's the problem.
    The CAZ needs to be checked for depressurization, then get the chimney checked. And I agree to put a low level CO monitor in there.
    But a gas water heater and a draft hood will always spill CO into the room. It is the poor design of it.
    Stick your personal CO monitor on top of your draft hood gas water heater on a windy day. It'll start beeping and showing high levels pretty quickly.

    There was an error rendering this rich post.

  • ryanwc
    ryanwc Member Posts: 50
    edited January 2023
    Thanks for the responses!

    We’ve had a standard CO monitor at the outlet closest to the WH in the living space. I just put it on an extension cord to perch it atop the WH and ran a faucet for a few minutes w/o incident. I’ll see if it rings when I take a shower. 

    There is a WH chimney issue I’ve been meaning to get fixed. Some knucklehead ran a flue pipe partway up the chimney. It stops 6 or 8 feet before the top of the chimney. This was noticed by the sweep when we had the chimney for our wood-burning fireplace swept. The pipes are in adjacent chambers. 

    The smell has not been constant, but frequent. I would note that it’s worst when the door is closed. I decided to open the door between the boiler room and living space, thinking it was a pressure issue. But understandably my wife worries that this is just dissipating the issue within the house rather than allowing it to escape up the flue. 

    One other test will be when the dryer is running, since that exhaust could be an additional cause of negative pressure. 
  • ryanwc
    ryanwc Member Posts: 50
    Any recommendations for a brand/model of low-level CO monitor?
  • SlamDunk
    SlamDunk Member Posts: 1,596
    Sensorcon. Look on Amazon.