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What size chimney? - Forno Bravo Forum: The Wood-Fired Oven Community


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What size chimney?

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  • What size chimney?

    I see it is 19 days since I posted my last thread and I have been unable to make progress on the oven because of damp weather. The delay has given me time to dream up some more questions as I visualize what the oven will look like at each stage.

    The Forno Bravo plans call for a 10" chimney for the 42" oven. My woodstove in the basement has a 6" stove with two 90 degree bends in it and it draws well. Is it really necessary to have a 10" chimney? Would a 6" suffice? Or an 8"?

    I am going with the herringbone layout for my hearth bricks, but I am considering cutting them at the opening to the oven and there laying down 1/2" vermicrete mortar to act as an insulating barrier before finishing the brick work out onto the landing in a regular pattern. Obviously the purpose of this extra work is an attempt to prevent heat loss from the hearth bricks out onto the landing part of the construction. The regular pattern bricks on the landing will be mortared in place then covered with a tile to give them a decorative finish. I anticipate having to cut down the thickness of the bricks in order to accommodate the tile and leave the surface flush with the hearth bricks. Does anyone have a comment on this idea?

  • #2
    1. re: the chimney; i would go with the recommended diameter. my 42" has an 8 inch pipe with some constriction in the throat and i get a fair amount of smoke out of the front during the early part of the fire. (cough).

    2. re: the landing; cutting the bricks to the right thickness sounds like a lot of work. i would suggest getting sheets of varying thickness of wonderboard or durock as an underlayment and then experiment to see what combination (ala layers of wedding cake) of wonderboard, brick splits and tile are necessary to bring the landing up flush with the hearth. (make sure to put the wonderboard on top for ease of laying your tile). you'll also have to allow for the thinset.
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    • #3
      Chimney and landing

      If your vent is pretty open, I think an 8" should do it. Robert, my guess is your airflow limitation is the size of the vent opening itself, not the pipe. What do you think? Would you agree with that?

      We recommend 6" pipe of the Casa80 (31") and Casa90 (35") and 8" pipe for the Casa100 (39") and Casa110 (43"). That said, there is no harm over-engineering anything.

      Personally, I like having the oven landing at the same height as the oven floor. It makes things a lot easier when you are moving pizzas and pans in and out of the oven. Robert's ideas are right. You can also pour a concrete hearth under the landing that is higher than the rest of the hearth (subtracting the thickness of the tile).

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      • #4
        Chimney size

        Thanks for the feedback.

        I will go with the 8" insulated steel pipe with a good sized vent to encourage air flow.

        I'll take heed of the suggestions for raising the landing area with materials other than cut bricks. It does make sense to make the landing and cooking surface the same height right through.


        • #5


          Sounds good on all counts. The double wall pipe stays hot inside, to keep down build up and draw well ("ensuring high flue gas temperatures for optimum draft performance" according to the manufacturer), and cool on the outside. We use DuraTech, by Simpson Duravent. We posted their installation PDF, and part #s, sizes, etc. here:


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