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Do I need to redo my dome height?

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  • Do I need to redo my dome height?

    I'm building my second oven, and I messed up the very center of the dome. I have a 12.5" door opening height and was shooting for a 20" dome height for the 63% door height to dome ratio Everything was going good until I got to the last 4 to 5 courses of brick. I switched from the indispensable tool to a pilates ball to finish the dome, but I realized too late this caused my dome to peak at the center. Now instead of a 20" center dome height, I have a 23" peak. Will this additional 3" greatly affect pizza cooking or should I demo the center and flatten it out? I'm leaning toward a redo of the center but don't want to do it if it's really not necessary. I expect the oven will be used about 75% for pizza and 25% for conventional cooking. Performance aside, the peak is not very aestetically pleasing, although I will be the only one to know this.
    Last edited by SteveP; 03-30-2021, 08:27 PM.
    My WFO project: http://picasaweb.google.com/stevprin/WFOSmallPhotos#

  • #2
    I don’t think you should alter it. Many builders are of the belief that the 63% door height to internal height is most important. My experience with altering this ratio has led me to believe that considerable departure from that ratio makes no measurable difference.
    A customer of mine requested a taller oven (mine are only 21” internal hemisphere). I cast a 2” high ring around the base and mortared the 21” diameter castings on top, raising the internal height by 2” as well as raising the oven mouth by the same amount. I was pretty uncertain what to expect, having altered the internal volume considerably as well as changing the door to height ratio. I was surprised to find that there was no difference in firing characteristics or oven performance compared to an unmodified oven. They did a stunning mosaic of Positano on the front by the way.

    Click image for larger version

Name:	Ryan and Teena's oven.jpeg
Views:	259
Size:	28.7 KB
ID:	436802



    Last edited by david s; 03-31-2021, 04:22 AM. Reason: added pic
    Kindled with zeal and fired with passion.

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    • #3
      Originally posted by david s View Post
      I don’t think you should alter it. Many builders are of the belief that the 63% door height to internal height is most important. My experience with altering this ratio has led me to believe that considerable departure from that ratio makes no measurable difference.
      A customer of mine requested a taller oven (mine are only 21” internal hemisphere). I cast a 2” high ring around the base and mortared the 21” diameter castings on top, raising the internal height by 2” as well as raising the oven mouth by the same amount. I was pretty uncertain what to expect, having altered the internal volume considerably as well as changing the door to height ratio. I was surprised to find that there was no difference in firing characteristics or oven performance compared to an unmodified oven. They did a stunning mosaic of Positano on the front by the way.

      Click image for larger version

Name:	Ryan and Teena's oven.jpeg
Views:	259
Size:	28.7 KB
ID:	436802


      Thanks for your feedback. I believe I will just leave it as is. I will be covering the dome with insulating blankets then adding a housing around it. If for some reason it doesn't work as well with this dome height, worst case scenario is just having to remove the roof and blanket to redo that section of the dome.
      My WFO project: http://picasaweb.google.com/stevprin/WFOSmallPhotos#

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      • #4
        BTW, that is a stunning mosaic on that oven.
        My WFO project: http://picasaweb.google.com/stevprin/WFOSmallPhotos#

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        • #5
          Originally posted by SteveP View Post
          I'm building my second oven, and I messed up the very center of the dome. I have a 12.5" door opening height and was shooting for a 20" dome height for the 63% door height to dome ratio Everything was going good until I got to the last 4 to 5 courses of brick. I switched from the indispensable tool to a pilates ball to finish the dome, but I realized too late this caused my dome to peak at the center. Now instead of a 20" center dome height, I have a 23" peak. Will this additional 3" greatly affect pizza cooking or should I demo the center and flatten it out? I'm leaning toward a redo of the center but don't want to do it if it's really not necessary. I expect the oven will be used about 75% for pizza and 25% for conventional cooking. Performance aside, the peak is not very aestetically pleasing, although I will be the only one to know this.
          A friend of mine did exactly the same thing. While it looked a bit odd prior to insulation and outer render, it works perfectly fine. Don't worry about it!
          My 42" build: https://community.fornobravo.com/for...ld-new-zealand
          My oven drawings: My oven drawings - Forno Bravo Forum: The Wood-Fired Oven Community

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          • #6
            I've found two comments about 50 % door to dome ratio and they both say it works.

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            • #7
              If you have a really small oven like mine (21”) the height of the oven mouth can be an important factor. In the case I posted about my oven mouth to internal height is 59% (I can just fit in a 4kg turkey and fine for a normal roast or sourdough loaf or two). The modified oven had a ratio of 66%
              At the other end a really big oven say 6 ft diameter would not require a door nearly 4ft high.

              It is also common for performance increase to enlarge the ports on cylinder heads and increase valve lift by camshaft modification thereby increasing inflow and outflow, particularly with hemispherical heads.
              We are doing similar with our ovens, just we have a much larger combustion chamber.
              Last edited by david s; 03-31-2021, 03:46 PM.
              Kindled with zeal and fired with passion.

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              • #8
                Originally posted by david s View Post
                If you have a really small oven like mine (21”) the height of the oven mouth can be an important factor. In the case I posted about my oven mouth to internal height is 59% (I can just fit in a 4kg turkey and fine for a normal roast or sourdough loaf or two). The modified oven had a ratio of 66%
                At the other end a really big oven say 6 ft diameter would not require a door nearly 4ft high.

                It is also common for performance increase to enlarge the ports on cylinder heads and increase valve lift by camshaft modification thereby increasing inflow and outflow, particularly with hemispherical heads.
                We are doing similar with our ovens, just we have a much larger combustion chamber.
                Thanks for the feedback. I had looked at either cutting off the top of the dome to flatten it out, then thought about making a rendering of refractory mortar and ground fire brick powder to apply to the top of the dome interior to lower the overall height. But, after reading the above comments, I'll just leave it and see how it performs. I can always scoot inside the oven to apply the mortar/fire brick powder to the roof if needed. I'm assuming this would stay once cured, but I doubt I'll do anything.
                My WFO project: http://picasaweb.google.com/stevprin/WFOSmallPhotos#

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                • #9
                  Originally posted by Petter View Post
                  I've found two comments about 50 % door to dome ratio and they both say it works.
                  I'm at 52%. I believe I'm really over thinking this.
                  My WFO project: http://picasaweb.google.com/stevprin/WFOSmallPhotos#

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