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  1. #1
    Join Date
    Oct 2010
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    Southwest US
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    Default 3-2-10 rule revisited

    Does the 3 feet above the roof line only apply to wood burning fireplaces, not to gas appliances? I can't find anything in the IRC regarding this.

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  2. #2
    Join Date
    Mar 2007
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    Near Philly, Pa.
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    Cool Re: 3-2-10 rule revisited

    chimneys

    Keep the fire in the fireplace.

  3. #3
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    Default Re: 3-2-10 rule revisited

    Thanks Bob. Does a prefabricated gas fireplace with type B vent count as a chimney? Is it OK to have type B vents 4-6 inches above the roof line?


  4. #4
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    Mar 2007
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    Near Philly, Pa.
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    Cool Re: 3-2-10 rule revisited

    Nope and nope.

    B-vent is a *vent*--not a *chimney*.

    Refer to the gas codes but they start at 12" above a flat roof then go up based upon roof pitch.

    Keep the fire in the fireplace.

  5. #5
    Join Date
    Oct 2010
    Location
    Southwest US
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    585

    Default Re: 3-2-10 rule revisited

    Thanks again Bob! Here is a picture of the vent I thought was too low. It's about 3 feet from the parapet and well below it but not within 3 feet of the corner. I am not sure I understand why a gas appliance would not back draft when a fireplace would? Any insight?

    Bvent.jpg

    Last edited by Benjamin Thompson; 04-29-2011 at 10:52 PM.

  6. #6
    Join Date
    Mar 2007
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    Near Philly, Pa.
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    1,643

    Cool Re: 3-2-10 rule revisited

    You have a vertical obstruction within 8ft horizontally so the flue gas outlet must extend at least 2 feet above the top of that parapet. The 3 ft rule is to allow sparks from wood burning to cool before they land on a possibly combustible roof deck. The 2/10 is to hopefully extend the vent above any pressure zones created by wind effect over a ridge.

    The height of a vent above a roofline would have an effect on backdrafting only if it was wind related in which case it may need to extend a lot more than just the code minimum. Codes do not guarantee performance and can be exceeded.

    Keep the fire in the fireplace.

  7. #7
    Join Date
    Mar 2007
    Location
    Ormond Beach, Florida
    Posts
    26,251

    Default Re: 3-2-10 rule revisited

    Quote Originally Posted by Bob Harper View Post
    ... code minimum. Codes do not guarantee performance and can be exceeded.
    Expanding on what Bob said - codes are the minimum standard, with the emphasis on "MINIMUM" standard. Any 'good' builder/contractor will exceed code as code is the crappiest they are legally allowed to build.

    Jerry Peck, Construction / Litigation Consultant
    Construction Litigation Consultants, LLC ( www.ConstructionLitigationConsultants.com )
    www.AskCodeMan.com

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