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Is it the Flue? - Forno Bravo Forum: The Wood-Fired Oven Community


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Is it the Flue?

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  • Is it the Flue?

    I built my arches yesterday for the flue and ended up with a flue opening of 4-1/2 inches by about 10 inches. Is this large enough for a 36 inch WFO or should I increase the size? Also is there a reason why you can't make a flue and chimney out of firebrick?


  • #2
    Re: Is it the Flue?

    The rule of thumb, such as it is, is that the opening should be twice the area of the flue. So if you are using a 8 inch flue tile (7 * 7 = 49) your 45 sq inch opening is actually constraining the flue. I'd plan on some smoke leakage on startup with those dimensions.

    There is no reason why you can't build your flue out of firebrick, except that flue tile is already made, and much cheaper than the ingredients of the hand built one. I would still build it with the half inch air space between the flue liner and the exterior masonry that code calls for.
    My geodesic oven project: part 1, part 2


    • #3
      Re: Is it the Flue?

      Maybe I am looking at this incorrectly. The opening in my brick arch is 4.5" by 10" and I was planning on a 6 inch round chimney. So should I increase the opening size (just need to trim 4 half bricks) by an inch or so along the length of the opening?



      • #4
        Re: Is it the Flue?

        Since it's already built, why don't you try it the way it is? The worst you'd have to do is re-do it, and the amount of smoke on start-up may not be a problem.

        A six inch pipe has a cross section of 28.25 sq. in., so your opening is wider. You may be fine. I'm not sure a little bevel along the edge is going to do any good.
        My geodesic oven project: part 1, part 2


        • #5
          Re: Is it the Flue?

          I agree with dmun. Carry on with what you are doing.

          You may get smoke coming out the opening when you are firing but the flue chimney combination you have should handle the hot gasses when cooking. The only down side is that you may have a certain amount of sooting up of the top outside of the opening.


          • #6
            Re: Is it the Flue?

            If the 8" pipe has an ID of 7" and the area is approx 22", I may be way overkill on my 5" by 20" opening for my 43” oven. I'm at the point where my width is set at 20", without removing a brick or 2. I can constrain the 5 inches to 4" and I'll be just over 3.6 times the flue area. I'm guessing that this isn't a bad thing, or at least not as bad as a flue that is inadequate for the fires that the oven will hold. I don’t know if a deeper opening, something like 9” by 9”, 81 square inches would be better than 4” by 20”, 80 square inches. It seems like I may be a bit narrow at 4” where I was comfortable at 5”.