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  1. #1
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    Oct 2009
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    UEi C155 - What level of 02 increase to tell if heat exchanger is cracked

    Is there a general consensus on how much the 02 needs to rise in the flue gases post blower turn on to point to a cracked heat exchanger?
    Also, has anyone heard of someone using this test on a natural draft furnace?

  2. #2
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    A rise in O2 when the blower starts is not always due to a cracked heat exchanger. Can also happen from other leaks in a furnace.

    Never condemn a HX on the combustion results alone, you need to verify it visually.

  3. #3
    Join Date
    Oct 2009
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    Quote Originally Posted by Chuck View Post
    A rise in O2 when the blower starts is not always due to a cracked heat exchanger. Can also happen from other leaks in a furnace.

    Never condemn a HX on the combustion results alone, you need to verify it visually.
    I've thought about this for a while and can't come up with any other pathway for more O2 to enter the flue than the HX. Please explain.

  4. #4
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    Air leaks around the vestibule panel on non-sealed combustion units. Also gasket leaks allowing air into the burner box on sealed combustion units.

  5. #5
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    Jul 2012
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    Cincinnati ohio
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    234
    Quote Originally Posted by bbuller View Post
    I've thought about this for a while and can't come up with any other pathway for more O2 to enter the flue than the HX. Please explain.
    Where there is supposed to be a silicone seal and it breaks down. I have personally never done one but hear goodmans are bad about this.

  6. #6
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    I had a few Trane/Am Std furnaces where the screws loosened slightly in the oval ports on the heat exchanger face where the flame enters. Caused a rise in o2 when the blower started.

  7. #7
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    To answer your original question, anytime there is more than .5% rise in o2 when the blower starts I am investigating to find out why.

  8. #8
    Join Date
    Oct 2009
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    29
    Gotcha. Thanks for the info. It made sense to me that on a non-sealed combustion furnace that you can have all sorts of ways to introduce O2 via the draft hood/box, but it was not initially clear how a sealed combustion unit would introduce 02 in any avenue than the heat exchanger.

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