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  1. #1
    Join Date
    Oct 2003
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    High CO counts from 90% furn. exhaust

    We have a natural gas company that uses high CO counts coming from the exhaust of a 90% furnace to indecate the furnace has heat ex. problems or possible cracks.
    What are normal CO counts for a NG furnace running correctly. If the furnace had a heat ex. crack the fact that more fresh air would be brought into the gases of combutions and so the CO counts would be less. Am I thinking this wrong. See what you guys think. Thanks for the help.

    Stupid is as stupid does. Don't be stupid!

  2. #2
    Join Date
    Feb 2003
    S.W. PA
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    i am not the expert on this subject but normal should be under 100 ppm
    @ 200ppm would suspect a problem
    and @ 400ppm it gets shut down

    i know there are other problem that will cause high co but bad heat exchanger is a big one

  3. #3
    Join Date
    Oct 2007
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    I consider a stable reading of 100 ppm or less to be safe. There are many possibilities as to why a furnace would create more than 100 ppm and many of them can be easily fixed or adjusted so that the CO is brought back to safe levels. The furnace may have a mechanical problem like you mentioned but it could also be that the furnace has burners or orifices that need to be cleaned, is over-fired or under-fired and needs the gas pressure adjusted, etc.

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