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Residue build-up in stack pipe when using a power venter

I was asked to service an oil fired warm air furnace equipped with a power venter. The customer complaint was a build up of a white or cream colored residue in the stack pipe. There was also a large accumulation of residue all over the burner assembly. It appears this mess leaked from the stack pipe above the burner assembly.
Does anyone know what this residue is? How does one prevent this mess from happening?


  • Richard D._2
    Richard D._2 Member Posts: 156
    What is

    the stack temp??? smoke??? Co2.....Could be too much air or a real lo stack temp!! Keep me posted on what you find
  • John@Reliable_4
    John@Reliable_4 Member Posts: 101
    Herb, could be afew things..........

    1)How long is flue pipe run? I have found that with long runs the the temp. cools down causing what you found.
    2) How much air? I find that with powervents allot of service techs add way to much air.
    3) When is unit serviced? I find that if serviced(brush&vac) right after end of season this stuff can't happen. also when we find it,we pull all flue piping and either replace it or water hose it out and get on an end of season service,with good results. Hope this helps John@Reliable
  • Alan R. Mercurio
    Alan R. Mercurio Member Posts: 588
    Herb, here's another possibility

    The following information is from Field Power Venters Technical Department

    During the summer, white crystals are form in the joints of the vent pipe. Why is this?
    This is normally a problem that occurs when an air conditioning system is installed. When the blower comes on, outside air is being drawn into the house through the power venter. The hot, humid outside air causes condensation to form in the pipe. The white crystalline material is usually zinc oxide. Zinc is used in the galvanizing process. The solution would be to use our MAS kit to bring in more outside air directly to the appliance.

    Your friend in the industry,

    Alan R. Mercurio

    Oil Tech Talk
  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    The stack temperature is too low.

    I'm finding the best way to check it is not only at the breech of the appliance, but also where the pipe enters the vent or chimney. With oil if it's not 350 F or more throughout, that's the problem and that's a FACT!
  • MikeR_3
    MikeR_3 Member Posts: 43
    Draft regulator?

    Where is the draft regulator? If it is at the furnace end of the pipe, cool basement air could be drawn in, thus lowering the flue gas temperature.
  • Mark Hunt
    Mark Hunt Member Posts: 4,909

    of the combustion appliance zone.

    Say that ten times fast!

    Now imagine what happens with an atmospheric draft system when the burner IS on!


    Man! Don't we play with dangerous stuff?!?!?

    Mark H

    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
This discussion has been closed.