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  1. #1
    Join Date
    Mar 2011
    Posts
    20

    is 'forced draft' same as 'direct vent'?

    The Field Controls Draft Control Guide recommends damper placement as close to the furnace as possible (but 12" beyond a stack switch) except for 'forced draft' systems. Is 'forced draft' another name for 'direct vent'?

  2. #2
    Join Date
    Dec 2002
    Location
    Toledo, Ohio, United States
    Posts
    12,896
    Twilly says no, although some may interchange them they are different
    No Heat No Cool You need Action Fast

  3. #3
    Join Date
    Feb 2010
    Location
    Ontario Canada
    Posts
    1,339
    IMHO direct vent is venting directly to the out side with the manufacture's limited length of vent and temination, with no forced or mechanically assisted venting. Forced draft would be as implyed, a fan assisting the exhaust flow.....

  4. #4
    Join Date
    Mar 2011
    Location
    Northeast Missouri
    Posts
    61
    Forced draft is when a fan (ex. combustion blower) is used to create a positive static pressure in the vent pipe to exhaust the combustion gas to the outdoors.

  5. #5
    Join Date
    Mar 2011
    Posts
    20
    Thanks for the clarifications.

  6. #6
    Join Date
    Sep 2008
    Location
    VA
    Posts
    1,716
    Forced draft is as "mizzo" suggested, a combustion fan used to produce a positive pressure in the flue.
    Draft assisted is different; it only induces the draft through the heat exchanger at a preset rate. Yes, it may result in a slightly positive draft neart the outlet of the combustion fan, but natural covection is used in the flue.
    A direct vent unit can be a configured as a forced draft. The difference is, a "direct vent" is only with both intake and exhaust taken from outdoors. Without the combustion air intake taken from outdoors, it's just a forced draft.
    "The only true wisdom is in knowing you know nothing" Socrates

  7. #7
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,052

    Cool

    mizz and mgen are correct.

    FYI, all positive vent pressure venting must be listed venting per the IRC. We on the Ul Standards Technical Panel are working on a US version of the Canadian S636 code for listed PVC venting. Stay tuned.

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