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gravity vent does not draw

Bob Harper
Bob Harper Member Posts: 1,091
in THE MAIN WALL
Lyle is partially correct with the 2/10 rule. However, there is also an absolute minimum of 3 ft even on a flat roof. Practically, it may need to extend even higher to get out of adverse wind conditions or increase the capacity to generate more draft.
Is the chimney lined? Terra cotta or stainless steel? Your chimney flue could be oversized. 272mbtu is not a lot for an 8" vent even at only 20 ft.
What about CAZ depressurization? Did you test for draft interference? You may need to perform a Worst Case Depressurization Test to guide your efforts.
Bump Timmie's comments on the CO spillage and alerting protection. Test it and correct ASAP!

Comments

  • Jim Wy.
    Jim Wy. Member Posts: 43


    I have a 272MBH boiler w/ an 8 inch flue about 20 ft. tall and 2 ft. above the roof line. It's not new construction and has an 8 in. combustion air intake. the vent cap is a cheap standard unit. When the wind blows 25mph the flue dumps into the mech.room & if the boiler is not running cold air blows out the draft diverter. Any ideas?
  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    Somehow

    the wind is creating a positive-pressure zone around the chimney top, forcing air into it.

    Does this only happen when the wind blows from a certain direction?

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  • Jim Wy.
    Jim Wy. Member Posts: 43


    Yes, it is at its worst when the wind blows from the north east but 25plus mph efects it somewhat reguardless.
  • Unknown
    Unknown
    Install a Field

    StarKap which prevents downdraft. I would also put a blocked vent/spill switch on the draft hood.

    Do you have CO detectors in this location?
  • Jim Wy.
    Jim Wy. Member Posts: 43


    yes we have co detecters . Could someone please describe a star cap? Where could I order one ?
  • bob young
    bob young Member Posts: 2,177
    star-kap

    Click here: http://fieldcontrols.com/pdfs/46263300.PDF also ameri-vent makes vent caps among others
  • Lyle {pheloa} Carter
    Lyle {pheloa} Carter Member Posts: 66
    Venting

    It's acting like it is not high enough above the roof line. It should 2 feet above the roof at a point 10 feet away . Measure horizontaly from 2 feet below the top of the flue to the nearest point of the roof . At this point should be 10 feet.
  • Edward A. (Ed) Carey_3
    Edward A. (Ed) Carey_3 Member Posts: 236
    Vent construction

    Jim,

    What is your 8" vent constructed of?

    Is it single wall metal, metal all fuel, masonry lined, masonry unlined chimney, etc.?

    You said it is 2' above the roof line. Please describe that termination and the proximity to the roof in more detail.


    Ed Carey
This discussion has been closed.

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