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what size chimeny - Forno Bravo Forum: The Wood-Fired Oven Community

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what size chimeny

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  • what size chimeny

    Hello to all ,
    I'm new to the forum such a amazing site so much information.I'm in the process of building my 1st pizza oven so excited ,but nervous I'm actually building it on top of an existing outdoor fireplace.I already have the pad poured ready for the fire brick's, it's 'about 52"-1/2w x 56"l 5'thick.I purchased the fire brick 9 x 4-1/2 x 2-1/2 and cut them in half, I also purchased 2'thermafiber insulation board k-fac19 for the base.The oven will be 36'inside dia. the door will be 10'high x 18 wide and the ceiling height is 16" which give's a door to ceiling height ratio of 62.5%. I still have to purchase the insulation for around the dome which will be 3" and then 2 more inches of refractory mortar.I have a couple of question regarding the chimney,flue and,vent.I want to use a 6" chimney but,don't know how tall to make it, 24"or 36". How big should the vent be? and,how much room do I need from the door to the outside of the arch way will one brick length do?.I get a little discourage sometime ,I'm a pretty good hands on guy just want to build it right, don't care how long it take .Am I headed in the right direction? Thanks to all Bruno

  • #2
    Re: what size chimeny

    There is not a set size or height for the vent chimney. Note that the functioning of the oven is pretty much independent of your vent. Many ovens are built with no vent at all.

    The primary purpose of the vent is to deflect hot gasses/smoke away from the face of the operator. When initially fired, the oven will produce a huge amount of smoke for the first 20 - 30 min or so. After that and during cooking much less smoke is produced.

    If you want to size your vent to deflect the large amount of smoke during firing it will need to be quite large.

    If you size it only for the smoke and gasses released during cooking, a 36 inch pompey will be fine with a 6 inch diameter flue about 18 inches or so high. You will get soot buildup on the outside but but you will get a certain amount of soot regardless of how big your vent is. Personally, I don't mind the soot and think it adds to the aesthetics.

    "I need from the door to the outside of the arch way will one brick length do?"

    This dimension only needs to be long enough to perch your vent on. With a 6 inch flue, one brick length (9 inches) should do.
    Last edited by Neil2; 04-10-2012, 01:26 PM.

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    • #3
      Re: what size chimeny

      The general rule of thumb is that the flue needs an area at least 10% the size of the oven opening.
      The English language was invented by people who couldnt spell.

      My Build.

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      • #4
        Re: what size chimeny

        Originally posted by brickie in oz View Post
        The general rule of thumb is that the flue needs an area at least 10% the size of the oven opening.
        No, I don't think this rule should be used. It may be OK for a fireplace, but not for a wood fired oven. For my oven, which is 21" it has a 5" flue which is 20% of the inner oven door.

        If you used the 10% rule for your 10x18 opening, you would end up using a 5" diam flue, which is clearly inadequate.

        A 6" flue should be ok for your oven, but go the extra height 36" for increased draw. Also try to keep the entry as shallow as possible to make handling the oven cooking easier.
        Last edited by david s; 04-09-2012, 04:38 PM.
        Kindled with zeal and fired with passion.

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        • #5
          Re: what size chimeny

          Originally posted by brickie in oz View Post
          at least 10%
          Like I said.
          The English language was invented by people who couldnt spell.

          My Build.

          Books.

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          • #6
            Re: what size chimeny

            Don't go any lower than 15% or you will have smoke staining all over the front of your oven, smoke in your face at start up and inadequate draw. Also try to have some funneling to the base of the flue pipe so there is room for the smoke to collect.
            If the flue is not performing properly, then there is little point in having one. In fact, because it requires the entry in front of the oven door it is already an inconvenience, so it would make sense to have it perform it's function.
            Last edited by david s; 04-08-2012, 09:30 PM.
            Kindled with zeal and fired with passion.

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            • #7
              Re: what size chimeny

              So should I leave maby a 6x10 opening below then drop the flue in,I will use a 6 x 36 flue How much room do I leave from the door to the outside of the oven?will 1 brick length do(9").
              Thanks Bruno

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              • #8
                Re: what size chimeny

                That would work. Personally I think a 5x12" opening would be better, then you can have your entry an inch shallower.You can then taper the vent to a 6x6" opening into which you can fit the flue pipe.
                Last edited by david s; 04-09-2012, 05:49 AM.
                Kindled with zeal and fired with passion.

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                • #9
                  Re: what size chimeny

                  That sounds Great,thanks for your help.
                  Last edited by Bruno D; 04-09-2012, 01:21 PM.

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                  • #10
                    Re: what size chimeny

                    Reading the forums I see many uses of a double walled chimney system (expensive). If I use a single walled chimney liner, and enclose the pipe in my dome covering "house" isolated from combustables - is there any loss of performance? ie does insulating the chimney pipe make it perform better?

                    The product I have in mind is at this link 316L Chimney Champion Rigid Chimney Liner Kit - 8" | WoodlandDirect.com: Chimney Accessories, Chimney Liners, Champion Ridgid 316L Chimney Liner Kits
                    dvm

                    My road to pizza is documented here:
                    http://www.fornobravo.com/forum/f21/...ome-17755.html
                    sigpic

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                    • #11
                      Re: what size chimeny

                      Originally posted by dvm View Post
                      Reading the forums I see many uses of a double walled chimney system (expensive). If I use a single walled chimney liner, and enclose the pipe in my dome covering "house" isolated from combustables - is there any loss of performance? ie does insulating the chimney pipe make it perform better?

                      The product I have in mind is at this link 316L Chimney Champion Rigid Chimney Liner Kit - 8" | WoodlandDirect.com: Chimney Accessories, Chimney Liners, Champion Ridgid 316L Chimney Liner Kits
                      DVM

                      Others that have done masonry chimneys and other enclosures this way with great success. You will want to start on an "Anchor Plate" and use a Top Plate and Storm Collar at the top to prevent leakage.

                      As long as you stay away from combustibles you will be OK.

                      You may want to check your local fire code also.

                      Chip
                      Chip

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                      • #12
                        Re: what size chimeny

                        I did not do this on my build, but it was one of my options.
                        Install a single wall SS flue pipe, buy galvanized pipe from Lowes or HD and fill the space between with V-crete or just vermiculite.

                        I did not figure the circumfrance of the outer pipe because I chose a different direction. They usually stock 4", 6", and 8" with interlocking seams. I figure that 2 of the sizes could be mulled together to achieve the space needed for insulation.
                        I don't care what folks say behind my back........They are either braggin' or.......lyin'

                        joe watson

                        My Build
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                        • #13
                          Re: what size chimeny

                          An interesting thought. I will "noodle" on the Idea of a DIY double walled chimney. When it comes down to it I may simply spring for the tried and true ss double wall model.
                          dvm

                          My road to pizza is documented here:
                          http://www.fornobravo.com/forum/f21/...ome-17755.html
                          sigpic

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                          • #14
                            Re: what size chimeny

                            I also was put off by the cost (and look) of the stainless steel chimney pipe and liked the idea of just stacking 8" flue tiles inside of 12" tiles. Just used some leftover hi-temp mortar to secure each inside tile to the one above it and bought a chimney cap with screen for spark arrest on top. My inside/visible section uses the same double flue tile but with an outside facade of brick to visually tie it to my oven structure.

                            I put a series of pictures below (before I enclosed the oven) to give you an idea how I built my chimney. The last shot shows you the simple stacking I used when I extended above my roof of the final outside, screened room.
                            Attached Files
                            Mike Stansbury - The Traveling Loafer
                            Roseburg, Oregon ( www.sablesprings.com )

                            Photo albums
                            (working on restoration after web site upgrade )

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                            • #15
                              Re: what size chimeny

                              That looks like a great solution. Did you leave the space between the flue tiles an air gap - or did you fill with vermeculite etc. I have not found a supplier in So Cal selling clay flue tiles (I have limited my search so far to Google - I have not yet broken down and simply called anyone on the phone).

                              dvm
                              dvm

                              My road to pizza is documented here:
                              http://www.fornobravo.com/forum/f21/...ome-17755.html
                              sigpic

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