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Cold Chimney

Jim Pompetti
Jim Pompetti Member Posts: 552
Outside wall B-vent chimney , it will not draft , Can I use a forced draft system.


  • Al Letellier_21
    Al Letellier_21 Member Posts: 402
    edited January 2011
    Cold Chimney

    Most appliances, but not all can be used on a forced or draft induced system but check with the manufacturer of your unit before you leap. Venting gas in nothing to play with....be smart and safe !!!
  • Eric_32
    Eric_32 Member Posts: 267
    edited January 2011
    Is your....

  • Eric_32
    Eric_32 Member Posts: 267
    Is your....

    Is your B-vent chimney exposed to the elements or is it enclosed in a "false chimney" looking box?

    We can't run exposed b-vent along side a building without enclosing it here in MA, at least that was what I was told the last time we did it years back.
  • Jack
    Jack Member Posts: 1,047
    You can add a draft inducer

    but what you are doing is putting a bandaid on poor design to begin with. While b-vent has been used outside for years it has become less and less successful since 1992 when system efficiencies were mandated on Catagory I appliances to be a min of 78%. On the old 60%-ers, you could get by a lot of poor design with a high stack temp to drive the flue gases. With the efficiencies of today more and more AHJ's do not allow it and the manuf of the pipe will tell you it is a bad idea as well, if they don't specifically prohibit it.

    If you do try a draft inducer, I'd recommend that you have a bit of pre and post purge on the unit.

    To edit the title of this post...all ready...What does the equipment manuf require. Start there as that will likely modify my heading
  • Brad White
    Brad White Member Posts: 2,398
    Just to be clear though

    B-Vent should always be under a negative pressure. Any use of a DI system would positively pressurize the downstream portions, at least until any natural draft forces took over. You could use B-Vent on the upstream portions, however.

    Eric and Jack hit upon what I would look for first as the root cause, too cold a stack to start with and also not adding another element to correct for something with a more passive solution.

    If outside the building enclosure, an insulated system is the first choice, we know. As Al said/asked, what does the appliance manufacturer require?
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • Tim McElwain
    Tim McElwain Member Posts: 4,608
    What is the temperature in

    your area? If it is below 20 degrees then double wall pipe can not be exposed it must be enclosed by a chase in order to properly insulate it from extreme temperatures. Is this a recurring problem or just when it is very cold?

    As for a draft inducer it could be placed on the termination of the vent if that is feasible then you would not have to worry about pressurizing the vent. If you are using an in-line inducer versus a direct power vent then it can be placed in the existing flue without any issues with positive pressure. As has been said however I would make sure it can be done from the manufacturer of the equipment.

    Is there any other equipment into the B vent? If so all must be interlocked.
This discussion has been closed.