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  • Top hotter than floor

    My pizzas burn on the top before the bottom cooks
    am I doing something wrong in the heating process

  • #2
    Do you have a way to measure temperature of your floor and dome, like an infrared thermometer? You don't say how hot your floor is, but without a way to judge temp it it going to be difficult to diagnose your problem.
    My build thread
    http://www.fornobravo.com/community/...h-corner-build

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    • #3
      Thanks for the reply my thermoter ran out of juice
      I think I have it figured out I watched some you tube
      videos this am

      Comment


      • #4
        Hello newbie here, I recently made my own woodfire oven and I feel I am going through the same issue. Where I feel my top is hotter than my bottom. I will need to get a heat meter. Also I feel I made my oven too high, would that be my issue. Hope I can attach a pic. Thanks for your input.

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        • #5
          We need more info on the oven, floor and dome insulation, what is dome made of? Has the oven been cured, Details on construction, etc.
          Russell
          Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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          • #6
            Originally posted by Vikoski View Post
            Hello newbie here, I recently made my own woodfire oven and I feel I am going through the same issue. Where I feel my top is hotter than my bottom. I will need to get a heat meter. Also I feel I made my oven too high, would that be my issue. Hope I can attach a pic. Thanks for your input.
            From the appearance of your oven in the pic it seems as though the flue is near the top of the chamber. If so then this is an updraft circulation system where the fire jumps straight for the flue. This results in the top of the chamber getting very hot while the bottom remains cold. Generally WFO's over centuries have been designed with a cross flow circulation system whereby the flame is pulled to the side and down, exiting at the front and utilising the full length of the flame to heat the whole oven in a much more even way with far less energy lost out the flue. Because your oven is also quite tall this uneven heat distribution is also exacerbated. If I'm correct then the modifications to get to good performance maybe extremely difficult. If I'm wrong, as my wife often reminds me, then it could just be that your oven is new and still moist. In that case the top of the dome dries out way faster than the bottom, creating a very large temperature difference, in which case long slow fires should be used until the whole oven is completely dry, when performance improves markedly.

            If your oven lacks underfloor insulation it is also extremely difficult to get the floor hot enough because the heat quickly conducts to the structure below.
            Last edited by david s; 07-07-2020, 08:22 PM.
            Kindled with zeal and fired with passion.

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            • #7
              Hello, thanks for the reply. The floor was made of a full layer of fire brick, the second layer was left hollow and filled in with glass and salt as previously seen in a you tube video. (It's said to hold and get hotter longer). As for the dome, after fire brick enclosure I put 1 layer of mortar, one inch thick fiber clothe, strapped with wire all around and another layer of mortar with sealant to protect from water/rain. I also did a layer of refractory mortar inside dome, which I let cure for one week and then did small fires everyday for a week. I do not have my door to cover opening, still working on it. Thanks

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              • #8
                Attaching pics of my floor, how I filled in with glass and thick grain salt. Covering with a layer of fire brick.

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                • #9
                  I can't tell from the pics but you didn't mention adding any insulation between the thermal mass of the floor and the hearth slab. If you didn't the base is sucking heat away from the oven and you would have to fire the oven much longer to get the bottom up to temperature.
                  My build thread
                  http://www.fornobravo.com/community/...h-corner-build

                  Comment


                  • #10
                    It is too bad you did not joins prior to construction. So here are some issues that are causing you grief. As JR mention, the use of glass, glass bottles, etc are very old school and not very efficient thermal conductivity aka K value (these You Tubes can lead people down a rabbit hole). For example, glass has a K value of 1.05 vs calcium silica board (which is used a lot on the forum and new technology) has a K value of 0.05. This means the glass will transfer heat away from the floor 21 time more than CaSi board, in essence glass is a heat sink. You don't really say exactly what this 1" woven glass cloth is. Even if it were 1" of ceramic blanket, min. recommended is at least 2" or a perlite/concrete mix (4" recommended). So bottom line, your oven is what it is and I am uncertain what you can do to resolve heat loss and temperature differential.
                    Russell
                    Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

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                    • #11
                      My apologies if I am not answering the questions asked. Per JR's question about bottom insulation, None was put besides the glass and salt. I can still reopen the bottom floor and remove the glass and properly put this casi board as suggested by Uthabeehive. Please direct me to where I can see how this is done. As for the dome I can probably do a brain operation and cut around and bring that height down about a foot. My real issue would be on where to put my vent. I can probably extend my entrance like JR did and reconstruct it in front. What do you guys think?

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                      • #12
                        I did mentioned that P or Vcrete is an option if your budget is constrained and you can put 4" of 5 part perlite or vermiculite to portland.
                        Russell
                        Google Photo Album [https://photos.google.com/share/AF1Q...JneXVXc3hVNHd3/]

                        Comment


                        • #13
                          I just found this on a different post.

                          How thick are the heater storage bricks, the ones I have seen used by the UK builders were about 25mm, for the floor you should have about 50mm so you may need to double layer if the 25mm version. The thickness gives you thermal mass or the ability of the oven to retain heat, too thin and the floor gets too cold to quickly.

                          I wasn't sure what you ment by thermal mass, but know I do. I guess it's only 2.5" the size of one brick.

                          Also the 1" ceramic blanket is all the put around the dome.

                          Thanks

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                          • #14
                            Originally posted by UtahBeehiver View Post
                            I did mentioned that P or Vcrete is an option if your budget is constrained and you can put 4" of 5 part perlite or vermiculite to portland.
                            Uthabeehiver, not quite understand your post, can you elaborate. Thank You

                            Comment


                            • #15
                              Hi Vicoski, I don’t think you have many choices apart from excepting your oven as it is ... or rebuilding it !
                              You have to many bad issues to easily put right.

                              You really need to change the dome shape, move the chimney and add proper insulation all around the dome and underneath as well.

                              The basic idea is to build a half round dome from dense material like fire brick or high heat concrete and completely cover that with low density material like vermiculite or ceramic matting.
                              This is done so the inner dome can absorb the heat and the outer layer will keep the heat inside the oven.
                              if you don’t have an outer layer of insulation then the heat will not stay in the oven and the oven will not get super hot .

                              The chimney should be outside of the dome and not inside at the top, as this will also allow all the heat to escape to quickly!

                              I am sorry to say but I think you need to start again.

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