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How Heat Works - Forno Bravo Forum: The Wood-Fired Oven Community

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How Heat Works

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  • How Heat Works

    I've been meaning to build this graphic for some time, and got around to it this weekend. The graphic below is a visual representation of how heat moves, and is stored in both a Forno Bravo pizza oven, and in a high mass bread oven. It's is based on my personal experience with a range of ovens, and reports from many owners of various types of ovens.

    There are a number of things that the graphic tries to capture, including:

    1. Why higher mass ovens require longer firing periods.
    2. Why insulation is so important to the traditional pizza oven -- as it comes in constant contact with high-heat on the outer edge of the oven chamber and floor.
    3. Why a pizza can maintain high heat while cooking a large number of pizzas.
    4. Why all wood-fired ovens, and most noteably bread ovens need time for the termperature to regulate before you bake bread.
    5. Why a high mass oven actually starts to cool down inside the oven chamber when you start cooking pizzas -- those BTUs are still filling up the rest of the oven chamber mass.

    Let me know if the graphic helps make this more clear.
    James
    Attached Files
    Last edited by james; 11-05-2006, 01:24 PM.
    Pizza Ovens
    Outdoor Fireplaces

  • #2
    Isn't anyone going to comment on my nifty graphic? Does it seem right to you?
    James
    Pizza Ovens
    Outdoor Fireplaces

    Comment


    • #3
      This is a nice graphical illustration of the theories of brick ovens we've talked about here. The question - for James or other bread oven owners with thermocouples - is what the oven is like at 3 hours - is it getting to suitable pizza temps then?

      Comment


      • #4
        Re: How Heat Works

        I just finished three hours at our local farmers market baking 90 pizzas and the oven was still doing great.

        This is a refractory barrel style oven with 3" of refractory. outside of the dome was 160 degrees F.

        Comment


        • #5
          Re: How Heat Works

          Do you know of anyone who can help me with calculating flue size when it comes to my indoor pizza oven that is in the process of being built!!!! HELP!!!!!!!!!

          Comment


          • #6
            Re: How Heat Works

            I'm having trouble with my indoor basement oven installation. I have a chimney top that is 30 feet from the basement where the oven is. What diameter flue do i need to feed through there to get the right flow for the oven to work properly. Anyone out there please help!!!!!!

            Comment


            • #7
              Re: How Heat Works

              To help, we need all of the details.
              What kind, round/barrel?
              What size?
              How tall will the chimney be (from top of oven to end cap)?
              Are we talking a straight up run or will you need curves?
              Every detail you can include.

              Also, being indoors you are going to have to follow local building codes, so that would be a good place to start.
              Wade Lively

              Comment


              • #8
                Re: How Heat Works

                Thanks for getting back to me. To give you all of the information that I have it is a rounded oven, with a 40 inch floor space and it is a 30' straight run from the top of the oven to the chimney cap. If you can help in any way I would appreciate it.

                Comment


                • #9
                  Re: How Heat Works

                  Also need to know the area of your oven opening, as proper sizing of the chimney is related to oven opeing size. The rule of thumb is a max of 1/10 ratio, meaning that the fireplace opening can be 10 times as large as the flue cross section. This ratio applies to the diameter of the flue, so if you use a square flue you will calculate the dia of the circle inside, as the corners will not flow much due the dynamics of circular airflow.

                  The good news is taller is better, so you should have a good draw. You want the vent opening in your arch to be as wide as possible to scavenge as much flow as possible. You want the area of the vent opening larger (at least 30%) than the area of the flue. Make the vent to flue transition as smooth as you can, a smooth and easy airflow path leads to more volume of flow and higher speed. You definietely want insulated chimney, at 30' I am sure Duravent is out of the question, but it may make good sense to use it for the first section. Just by going on oven size since opening is unkown, you might be able to use 6" (113 sq in), but 8" (201 sq in) is probably a better choice. Just remember as you go up any transitions need to be the same area or smaller, do not go larger.

                  Again, make sure you know what the code requirements are, as they may make a lot of the decisions for you.

                  Hope that helps.
                  Last edited by wlively; 07-23-2009, 06:36 PM.
                  Wade Lively

                  Comment


                  • #10
                    Re: How Heat Works

                    Originally posted by wlively View Post
                    To help, we need all of the details.
                    What kind, round/barrel?
                    What size?
                    How tall will the chimney be (from top of oven to end cap)?
                    Are we talking a straight up run or will you need curves?
                    Every detail you can include.

                    Also, being indoors you are going to have to follow local building codes, so that would be a good place to start.

                    please help, can you give us your number so that we can contact you on this. I am only relaying info from my husband and I think he needs to personally talk to someone over the phone to get a better understanding of this job. My personal email is meranteboys@comcast.net Thanks, Domenica

                    Comment


                    • #11
                      Re: How Heat Works

                      Hello,

                      Im working on an oven that is set on a trailer... WOrking with the size trailer bed we have 46x48" I had decided on an oven diameter of 32"... now looking at it, it seems small... I wanted to change the shape a bit to make it 35x38" oblong/oval but am afraid that will mess up the heat flow etc... can anyone share their experience with a non-perfect circle oven? Or their thoughts on how this small difference will affect the cooking of pizzas? This oven is intended for that, not baking. thank you!!!

                      Comment


                      • #12
                        Re: How Heat Works

                        Sorry for the late reply.
                        You will come across many reports that say oval ovens work fine.
                        I offered to build my mate an oval one but he felt he would not be able to reach the back.
                        Our hosts, FB, offer an oval oven.
                        Artigiano120 Brick Oven Specifications

                        If using an indispensable tool, you could easily build an oval oven simply by using two pivot points.

                        Comment


                        • #13
                          Re: How Heat Works

                          Originally posted by wotavidone View Post

                          If using an indispensable tool, you could easily build an oval oven simply by using two pivot points.
                          Unless you have a string connecting the two pivot points with the inner dome contact point you'll end up with two hemispheres joined by a barrel arch. Another simpler way is to shape the oval dome in sand and build against the sand form.
                          Kindled with zeal and fired with passion.

                          Comment


                          • #14
                            Re: How Heat Works

                            Originally posted by david s View Post
                            Unless you have a string connecting the two pivot points with the inner dome contact point you'll end up with two hemispheres joined by a barrel arch. Another simpler way is to shape the oval dome in sand and build against the sand form.
                            So the shape will be two half hemispheres joined by a straight section rather than a true oval. So what?
                            I didn't explain my idea in much detail, but I believe I could make the whole dome in running bond, no centre arch making up the straight section.
                            I wanted to try it on my mates oven but he vetoed it on account of his short arms.
                            Maybe I'll get to try it on oven number three.

                            Comment


                            • #15
                              Re: How Heat Works

                              No, nothing really wrong with two hemispheres joined by a straight barrel. I was simply trying to clarify the geometry. A string that is movable between the three points would give you a true ovoid form.
                              Kindled with zeal and fired with passion.

                              Comment

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