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Retrofitting under floor insulation - insulation thickness and door/dome ratio - Forno Bravo Forum: The Wood-Fired Oven Community

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Retrofitting under floor insulation - insulation thickness and door/dome ratio

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  • Retrofitting under floor insulation - insulation thickness and door/dome ratio

    Hi All,

    I am looking for advice on the thickness of the insulation layer to add under our 4 piece oven floor. Current dimensions are 29cm door height and ~40cm dome height (72.5%). The floor is not insulated at all (the dome of the oven is highly insulated) and I am trying to figure out the optimal thickness of the superisol board to slide in under the floor (within the confines of the dome, which will itself unfortunately sit directly uninsulated on the a 20cm thick concrete slab).

    The 40 cm superisol board insulates from 500c to 67c. I would guess that a 50cm (2 inches) board would insulate from 500c to ~50c. If I add in the 5 cm superisol board, my door height would shrink to 24cm and the dome height to 35cm (68.6%). Does that seem like a reasonable approach?

    Do I have to leave any expansion room for the superisol board? If not it would seem preferable to jam it in as snugly as possible. The super isol board will have a seam in the middle (dictated by the size of th door opening of the built oven). Thanks in advance.

    I would Ike to be able to cook as many pizzas as possible without having to recharge the floor and I'd also like to bake bread at some point.

    The backstory:

    I went on vacation with my builder building the pizza oven (a modular Zio Ciro 90cm 4 piece round oven kit - http://www.zio-ciro.com/UserFiles/Fi...vesuvio_en.pdf). That was a mistake as it turns out. I had given him both the Rado Hand CD and a pizza oven design book as reference.

    In any case, the end result is a built pizza oven with (a) ~6 inches of refractory cement/vermiculite insulation and a ceramic insulating blanket over the *DOME* and (b) the dome and 4 piece oven hearth lying directly on a ~10inch concrete slab. From what I have read, that means that the oven (in its current state) is going to be a beast to fire since the concrete slab will act as a heat sink.

    The floor elements can be removed, since they are currently lying directly on the concrete slab. The edges of the floor elements will have to be trimmed to fit back into the dome, but should not be too dramatic. How much space should I leave between the floor pieces edge and the modular dome? Looks like there is nearly 1 cm of space there now.

    Appreciate any advice.

  • #2
    Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

    Removing the first floor tile might be quite difficult because as soon as you lift one edge it might lock in on the other edges. You could try drilling three holes in it and insert some masonry anchors so you can keep the tile level while lifting it. Once you have one out the others should be able to be removed easily.You can easily fill the holes in the tile with some refractory mortar (home brew would do)
    Kindled with zeal and fired with passion.

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    • #3
      Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

      Even though the "edge" of your dome sits directly on the concrete, you will have achieved a pretty high level of insulation.

      "If I add in the 5 cm superisol board, my door height would shrink to 24cm and the dome height to 35cm (68.6%)"

      You will be getting close to the optimum ratio of 63%. Getting the floor units up and out should be interesting. As David notes, if you tilt them they may jam. Perhaps consider raising the first one up using very long tapered wedges.
      Last edited by Neil2; 08-11-2012, 05:02 PM.

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      • #4
        Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

        Originally posted by Neil2 View Post
        Even though the "edge" of your dome sits directly on the concrete, you will have achieved a pretty high level of insulation.

        "If I add in the 5 cm superisol board, my door height would shrink to 24cm and the dome height to 35cm (68.6%)"

        You will be getting close to the optimum ratio of 63%. Getting the floor units up and out should be interesting. As David notes, if you tilt them they may jam. Perhaps consider raising the first one up using very long tapered wedges.
        Thanks, David & Neil2 for the feedback. I hope the floor tiles will yield to one of those two methods. I'll report on how it goes.

        What does the higher percentage ratio mean in terms of oven performance? Thanks.

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        • #5
          Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

          What does the higher percentage ratio mean in terms of oven performance? Thanks.[/QUOTE]

          If you were able to measure the difference in performance, I doubt whether you'd record any difference. Certainly none that you will notice.Don't worry about it.
          Kindled with zeal and fired with passion.

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          • #6
            Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

            Originally posted by david s View Post
            If you were able to measure the difference in performance, I doubt whether you'd record any difference. Certainly none that you will notice.Don't worry about it.
            Thanks. My door height is 1-2cm too high.

            I was able to get the floor tiles out with the help of a crowbar and some long sticks without too much trouble. Now to order the Super Isol board...

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            • #7
              Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

              "What does the higher percentage ratio mean in terms of oven performance?"

              The 63% ratio is cited as being optimum for oven efficiency. A slightly higher ratio implies you might use a bit more fuel but will still burn clean. A significantly lower ratio could lead to less complete combustion and possibly a sootier oven.

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              • #8
                Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

                If you double the thickness of the insulation ie 100mm you will end up with exactly 63%, still have a good workable door height, a dome that is closer to your pizza and a really well insulated floor.
                Kindled with zeal and fired with passion.

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                • #9
                  Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

                  Originally posted by david s View Post
                  If you double the thickness of the insulation ie 100mm you will end up with exactly 63%, still have a good workable door height, a dome that is closer to your pizza and a really well insulated floor.
                  Hi David,

                  Excellent point. What about adding a layer of firebricks under the floor tiles? Seems like 5cm of insulation should be adequate. The floor tiles are only 6cm thick. Adding ~3cm of fire bricks would at least add to the thermal mass for bread and residual heat cooking.

                  The fire bricks I have seen here are not exactly straight. Can I use sand under the floor tiles for leveling purposes?

                  Thanks.

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                  • #10
                    Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

                    Yes you could do both those things. Personally I think 60mm is plenty for the floor. 50/50 sand, fire clay is the usual mix for leveling the floor bricks.
                    Kindled with zeal and fired with passion.

                    Comment


                    • #11
                      Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

                      Originally posted by david s View Post
                      Yes you could do both those things. Personally I think 60mm is plenty for the floor. 50/50 sand, fire clay is the usual mix for leveling the floor bricks.
                      Thanks again for the feedback. The 50cm SuperIsol boards are cut, trimmed, and installed. The builders took the 4 floor pieces to trim the flat edges of each floor piece by 0.5-1cm, so that there will be 1-1.5cm of expansion room between the floor and the walls of the dome. Then the floor pieces will be put back in and the curing will continue. I am attaching two pictures. Thanks again for the advice here. Incredibly helpful.

                      The metal parts of the roof will be painted terracotta color and the oven structure will be covered with stone.
                      Attached Files

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                      • #12
                        Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

                        Looking good. Suggest you bake bread and roast for several firings before taking it to pizza temperature.
                        Kindled with zeal and fired with passion.

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                        • #13
                          Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

                          Thanks, David. Yes, will be taking it verrrry slowly up to cooking temps. Still have a long way to go on that front.

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                          • #14
                            Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

                            Quick question. Insulation boards are in place and trimmed floor pieces are installed now too. I was hoping that we could do the alignment such that the seams of the floor pieces would not meet up with the seam of the Super-Isol semicircles. It didn't work out that way, unfortunately. Would you be concerned about the heat loss from the seams nearly lining up? Thanks.

                            Did my second curing fire today. Woo hoo!
                            Attached Files

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                            • #15
                              Re: Retrofitting under floor insulation - insulation thickness and door/dome ratio

                              those joints will fill with ash and a very small surface area, little or no effect.
                              Our Facebook Page:http://www.facebook.com/pages/Stoneh...60738907277443

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