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flue gas question

My b vent does not behave like other flues (say clay liners) in the neighborhood. When my furnace is firing I see nothing coming out of the top. I had a combustion analysis by ugi and all test were good. Is there a reason why some gases are visible in the cold and others are not 


  • Tim McElwain
    Tim McElwain Member Posts: 4,628
    All products of combustion that

    vent out of the flue are not visible, the only thing that becomes visible is the water vapor which is created in the combustion process. Type "B" double wall pipe has much higher insulating qualities than say a clay tile liner chimney. That is why B vent is better for venting. The B vent takes less time to develop temperature difference called "Delta T" which along with the height of the vent is what creates draft. That may mean many times that no visible vapor can be seen escaping the vent. Wait for a real cold morning and then go look you then may see some vapor or Plume as it is often called.
  • bennythepitbull
    bennythepitbull Member Posts: 37
    edited November 2010
    thanks much Tim

    thanks much Tim
  • icesailor
    icesailor Member Posts: 7,265
    Flue Gas:

    Actually, it has a lot to do with the temperature of the flue gas, the amount or moisture in it and the dew point. Your flue gasses could be far different than your neighbors and chimneys with flues have different characteristics than "B" vent.

    Tim knows.
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