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Chimney Questions(s) - Forno Bravo Forum: The Wood-Fired Oven Community


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Chimney Questions(s)

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  • Chimney Questions(s)


    Planning this build for next spring but still planning ahead.

    Building the 36" - the FB plans say a 6 inch chimeny is okay - just wanted to confirm given the info below.

    I'm building the oven under/near my pergola so the chimney has to extend 2-3 feet above that (and the pergola is quite tall). I'm thinking I'll need an 8-10 foot chimney - planning on a duratech double wall system.

    Any issues with the chimney being that tall? (I should be able to provide support half way up)
    Will the 6 inch dia still be okay?

    Thanks in advance

  • #2
    Re: Chimney Questions(s)

    Tall is OK, in fact the taller the better the draw.
    Wade Lively


    • #3
      Re: Chimney Questions(s)

      I too used the 6". In my opinion it works perfectly...of course, I don't have anything to compare it to.
      I can say it draws very well with very little smoke in the face, and that is only on start up. I've found fire building to be an art; the right combination of DRY materials, placed on the fire at the right time, leads to nearly zero smoke.


      • #4
        Re: Chimney Questions(s)

        I need to insert a question as well on this subject. My opening is 6 x 13 inches, I can buy a flue that will fit - I was thinking I would go vertical 18 - 24 inches. Do I need to taper the flue as I ascend, or would the gasses draw just going straight up ? This part of physics is outside of my pay scale.

        Check out my pictures here:

        If at first you don't succeed... Skydiving isn't for you.


        • #5
          Re: Chimney Questions(s)

          Hi Dick,
          I built a 40"Pompeii and used 3 sections of 8" flue. See:

          I get absolutely no smoke out the front of the oven face as the vent and chimney draws exceptionally well.
          I have just pushed them together and not even rivetted nor screwed them together and have had no problems what so ever.
          I agree with RT and there is a science in setting a fire that produces the least amount of smoke. All dry wood, plenty of kindling to get that initial heat and no smoke. I made 2 stands that hold one end of the wood higher and allows the air to get in aqnd under the flames and works a trteat. Much quicker and hotter fires. I also found that you need to almost constantly tend the fire until you load the dry split logs or hard wood which wil take time to burn down to the coals which I then spread around the hearth. When almost ready to cook pizzas, I push the coals to the back and put 2 or 3 fresh aplit hardwood logs on which catch almost instantly, sweep the hearth and cook away.

          Prevention is better than cure, - do it right the first time!

          The more I learn, the more I realise how little I know

          Neillís Pompeiii #1
          Neillís kitchen underway


          • #6
            Re: Chimney Questions(s)

            I have a question about the size of the flue. The following is what is in the manual. "Depending on the type of chimney system you are using, you can either leave a roughly 6"x10" opening for use with a rectangular refractory chimney flue liner". However the smallest size flue I could find is 8"x12". Is this size flue too big and will it cause a problem?
            Thanks in advance


            • #7
              Re: Chimney Questions(s)

              I believe mine was 8 x 19 (I can measure it tonight). It appears to be venting pretty good. I am going to go another section up as well, I'm curious to see how it improves the draw.

              Check out my pictures here:

              If at first you don't succeed... Skydiving isn't for you.


              • #8
                Re: Chimney Questions(s)

                You shouldn't have any problem finding 8 by 8 flue tile, it's the most common size, used for woodstoves, furnaces, and a lot of other applications. 8 by 12 is the next size up, and it's most often used for open hearth masonry fireplaces. You should be able to use it, but it's more cost and weight than you need to use.
                My geodesic oven project: part 1, part 2


                • #9
                  Re: Chimney Questions(s)

                  The flue being larger is not a problem. Smaller can cause some concern but not larger.
                  Do not meddle in the affairs of dragons, for you are crunchy and taste
                  like chicken...

                  My 44" oven in progress...


                  • #10
                    Re: Chimney Questions(s)

                    Hmmm well as with most things, it depends.

                    In this case it depends upon the space that precedes the chimney. I had used an 8x12" chimney (two 3' lengths) and the draw wasn't bad, but it wasn't good either. I cut it down and replaced it with an 8x8. The difference was dramatic and I owe the improvement to assistance from Wlively and Dutchoven and their introducing me to Bernoulli's Law as it pertains to constructing vents and chimneys. Here is the thread started by James



                    • #11
                      Re: Chimney Questions(s)

                      Thanks everybody for your help. I did find 8x8 flue and installed it today but ran into two small problems. One problem was me being impatient and installing the chiminey before the mortar was totaly set. I am using a premix mortar that I got from a local company. We stacked two 8x8 flue pieces in place for the chiminey. The chiminey held and we were proud, so we went out to lunch. Then came the other problem, while at lunch we got hit with an unexpected rainstorm. The mortar got wet and weak. The arch gave way and the chiminey came tumbling down. Nothing broke and no one was hurt but a dumb move on my part. Any and all advice will be greatly appreciated. I will put up some photos later.


                      • #12
                        Re: Chimney Questions(s)

                        Just take a breath and start again...doesn't hurt to leave in the arch form until the mortar is thumbprint firm. That is a mistake you make only one time...my outer doorway arch fell and thereby was built twice...no worries!
                        "Making the simple complicated is commonplace; making the complicated simple, awesomely simple, that's creativity. " Charles Mingus
                        "Build at least two brick ovens...one to make all the mistakes on and the other to be just like you dreamed of!" Dutch


                        • #13
                          Re: Chimney Questions(s)

                          I agree with Dutch. You are the newest member of the broken arch club. I'm in the club, too.

                          Please post pictures of the aftermath too if you have them. I always enjoy a good catastrophe. I'm with ya - someone has a signature on the site that says something like anything worth doing once is worth doing twice.....

                          Hang in there!!!

                          Last edited by christo; 07-31-2008, 04:47 PM.
                          My oven progress -


                          • #14
                            Re: Chimney Questions(s)

                            Thanks for the support. I put the chiminey back up on Saturday and all is well. I should be able to start the curing fires on Sunday. I do not have any photos of the fall. Thanks again.