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  1. #1
    Join Date
    Jan 2013
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    Gas Smell through Vents when Furnace Starts

    Hello for the past couple weeks I’ve been noticing a faint natural gas smell coming from the vents just as the furnace turns on. This occurs at numerous registers throughout the house. 80% furnace put in in 2002.
    I called the gas company, who came out with their tools, but we couldn’t reproduce the occurrence. They did check all of the gas lines and connections but found nothing.
    I proceeded to call a family recommended HVAC company who came out, performed a diagnostic and also couldn’t find anything wrong. They did indicate that the heat exchanger passed all of their tests. The HVAC company indicated that the only thing left to check was the ductwork, which they didn’t do and didn’t have a recommendation, which seemed odd. They did mention a duct cleaning company might be able to help but I’m hesitant to use them.
    One thing they did note was that the air filter was really dirty and there was a piece of plastic on it within the plenum. I took a look at the filter and recognized the debris as coming from the install of our new roof. I went into the attic to check for any damage to the ducts that supply the furnace air but I couldn’t inspect all of the ducts as there is a bulkhead between the garage and house that I couldn’t get through.
    Note that the furnace is located in the garage. Also note that the HVAC blower runs 24/7, it’s supposed to be on a timer to limit the circulation period but the relay failed in the on position.

    Questions:
    -Would a compromised duct in the attic cause a gas smell?
    -are there specific companies that just repair/install ducts? I’ve searched the Seattle area to no avail.
    -is there anything else that may cause this smell?
    -am I warranted to be weary of duct cleaning companies?

  2. #2
    Join Date
    Jan 2010
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    Was the smell not present when the gas company was there ?
    Is it a natural gas smell or a methane gas smell ?
    Hot water tank near furnace ?

  3. #3
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    Thread Starter
    Unfortunately i wasn’t able to get the smell to show up when either gas company or HVAC company was there. It’s most consistent in the morning or when it hasn’t been run in awhile.
    To me, it’s the same smell as I get before the stove lights.
    Yes. Hot water tank is right next to the furnace.

    Thanks!

  4. #4
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    Jan 2010
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    Is your furnace exhaust pipe plastic or metal to a chimney ?

  5. #5
    Join Date
    Dec 2014
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    Did either do a combustion analysis?
    Get them out first thing a.m. to do the above. Leave it off for tonight

    Sent from my SM-G950U using Tapatalk

  6. #6
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    Thread Starter
    Metal exhaust pipe which has been reconnected at the roof level recently due to the roofers.

    I didn’t ask the HVAC company if they performed a combustion analysis. I don’t think the gas company did, but he did stick the probe into the furnace.

  7. #7
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    Jul 2007
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    Quote Originally Posted by Surprise View Post
    Hot water tank is right next to the furnace.
    Quote Originally Posted by Surprise View Post
    Metal exhaust pipe which has been reconnected at the roof level recently due to the roofers.
    I didn’t ask the HVAC company if they performed a combustion analysis. I don’t think the gas company did, but he did stick the probe into the furnace.
    Do you have any Carbon Monoxide (CO) monitors in the home? Preferably "Low Level" CO monitors that will indicate at levels starting at 5 -10 ppm.
    Last edited by rundawg; 03-23-2020 at 08:44 AM.
    Instead of learning the tricks of the trade, learn the trade.

  8. #8
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    Jan 2013
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    Thread Starter
    I do have carbon monoxide detectors, one battery and 4 fire/co combination. None are the ultra sensitive type though.

  9. #9
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    Aug 2002
    Location
    Southold, NY
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    Quote Originally Posted by Surprise View Post
    I do have carbon monoxide detectors, one battery and 4 fire/co combination. None are the ultra sensitive type though.
    You realize those detectors are worthless with CO at 69 PPM and wont alarm until 70 PPM for 1 hour continues.

    25 PPM for a few hours is dangerous!

  10. #10
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    So we have a 80% gas furnace. Tell us how the return air is ducted. Is there a duct for the return or just a filter and no duct ?

  11. #11
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    The return air comes from two inside the house grills that attach to 8? or 10? ducts run in the attic to the garage where the furnace is located. The air filter is located just above the furnace.

    The supply ducts are routed in the crawl space.

    I hope that helps!

  12. #12
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    Aug 2002
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    Quote Originally Posted by pecmsg View Post
    You realize those detectors are worthless with CO at 69 PPM and wont alarm until 70 PPM for 1 hour continues.

    25 PPM for a few hours is dangerous!
    Attached Images Attached Images  

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  14. #13
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    Thread Starter
    Thanks for everyones help. CO is definitely not something to mess around with. Thats why Im here trying to get as much help and assistance as possible.

    Side not: a combustion analysis was performed by the HVAC company and it seemed to have passed this analysis.

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