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  1. #1
    Join Date
    Nov 2009
    Posts
    5

    Rust on vent pipe

    I have a Trane 80000 btu 80% install horisontaly in my attick in MA
    There strange staf on vent pipe and traces of a drops of rusty color ander pipe conections.Instal is 10 years old.
    whole system starts with 90 elbo than 24" straigt pipe 45 degre elbo and
    36" pipe going up at the engle it all single wall 4" up to this point ,then increeser and 5" T caped on one side and going into the roof from other end.
    As you can see most of the rust is around the cap
    What may couse this and what is the best solution?
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  2. #2
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,765
    in an unconditioned space all venting should be double wall pipe.

  3. #3
    Join Date
    Dec 2004
    Location
    Derby City
    Posts
    3,973
    alex, I don't know what your local code calls for but here the flue pipe MUST be double wall class "B" to within 3' of the drafthood whether the furnace and / or vent pipe is in conditioned space. What is on the venting appears to be from conensate. There are AGA (American Gas Association) vent tables that clearly indicate what size venting is required. This takes into account the btu capacity of the appliance (in this case the furnace) as well as both the horizontal length and vertical length of the venting. If the venting is not properly sized and installed, then the water vapor that is a natural by-product of gas combustion condenses in the vent pipe before it can vent out. The condensationn would be internal in the vent piping.

    I don't understand the increaser to 5" with the one side capped unless this was supposed to be for venting an additional applicance (such as a water heater) at one time. Sounds like the flue was sized for this, and then when the other appliance was not added, it made the existing flue oversized.

    You should be able to get a reliable contractor (whoever you would normally call for service) to take a look at this and make recommendations.

    All the best, Irish
    Everyone has a purpose in life..........even if it's to be a bad example.

    Seek first to understand, before seeking to be understood.

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