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Vent Opening Size and Construction - Forno Bravo Forum: The Wood-Fired Oven Community

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  • Vent Opening Size and Construction

    I am starting to think ahead to the vent design and construction and have a few questions and I can't find the answers in other threads.

    First, is there a vent opening size ratio? In other words, if I am building a 42" high dome oven (and I am) and use the opening size of 20"x12.5" as recommended, do I need a vent opening size of ? square inches?

    Second, if I opt for the concrete vent construction do you need a special concrete mix or just basic concrete mix?

    Thanks in advance

  • #2
    Re: Vent Opening Size and Construction

    I think you take the square inches of the inner arch and use 10% of that for your vent opening. Just as your inner arch height is 63% of the dome height (the so called golden mean). As far as planning ahead, think of the inner arch. I think the whole dome is built around it.

    Good Luck

    Tom

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    • #3
      Re: Vent Opening Size and Construction

      That does not sound right to me. by your calculation that would be 250 square inches of the opening (if rectangle and not arched) 10% is 25 sq inches of vent so that is like a 5"x 5" opening? I'm no expert but that sounds small to me.

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      • #4
        Re: Vent Opening Size and Construction

        Originally posted by lhuhn View Post
        Second, if I opt for the concrete vent construction do you need a special concrete mix or just basic concrete mix?
        Yes, you need to use refractory cement mix as the vent gets extremely hot.

        I designed and molded my vent using Rutland castable refractory cement.
        George

        My 34" WFO build

        Weber 22-OTG / Ugly Drum Smoker / 34" WFO

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        • #5
          Re: Vent Opening Size and Construction

          Yes, you shouldn't use portland concrete for your vent transition. Way too hot.
          My geodesic oven project: part 1, part 2

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          • #6
            Re: Vent Opening Size and Construction

            The 10% ROT is for fireplace openings/flue size, but the same principle applies. It is always better to err on the side of larger, though.

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