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Heat loss through exposed floor at front problem? - Forno Bravo Forum: The Wood-Fired Oven Community

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  • Heat loss through exposed floor at front problem?

    Hi folks,

    When pouring my vermiculite layer, I left some room at the front for a facade as I didn't want the vermiculite exposed at the front. I was intending to use firebrick (same bricks as for oven floor), to build a decorative facade in front of the vermiculite layer and below the oven opening... the arch would rest partially on this facade...

    Now I'm thinking that this would create a thermal path through the floor and down to the hearth bypassing the vermiculite layer... am I over thinking it, or might this be a significant issue?

    Thanks in advance.
    My oven on a pallet build thread

  • #2
    Re: Heat loss through exposed floor at front problem?

    A photo might help. If your decorative arch is totally separated by say 10 mm this gap can be filled with vermicrete and provides quite a good insulation. I can hold my hand against the outer decorative arch after the oven has been cranking for an hour and a half. It's certainly better than having it connected where you get good conductive heat transfer. Using fire brick for the decorative arch is not a good choice as any smoke staining will be impossible to remove. Glossy tiles are better and will clean off well with some damp newspaper.
    Last edited by david s; 05-23-2014, 01:55 AM.
    Kindled with zeal and fired with passion.

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    • #3
      Re: Heat loss through exposed floor at front problem?

      Thanks David,

      I only have the vermi layer down so far.

      I was planning to seperate the dome from the entrance - I was more thinking of the fact that the arch will be connected to the floor thermally and the floor is connected thermally to the base via the bricks below the arch.

      I've attached a diagram.

      Do you think this is a problem?

      Edit: update the attached image
      Last edited by di11on; 05-23-2014, 02:19 AM.
      My oven on a pallet build thread

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      • #4
        Re: Heat loss through exposed floor at front problem?

        No that looks fine to me. I think you are over worrying. You've isolated the dome and floor pretty well. just be careful about drying the vermicrete layer before covering over it and locking in the moisture. Attached is an experiment I did which demonstrates how important this is. Sun and wind can do a lot of the drying for you but you need to give it some time.
        Attached Files
        Kindled with zeal and fired with passion.

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        • #5
          Re: Heat loss through exposed floor at front problem?

          You will be fine....My design is very similar and I have not had a problem.

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          • #6
            Re: Heat loss through exposed floor at front problem?

            If you re going through to the trouble of creating a heatbreak between the dome and entryway, you may want to slide a few IFB between the floor bricks and entryway bricks. Since they will be in direct contact, there will be some amount of heat transfer to exposed entryway bricks. How negligible this is, I don't know. I did it to be safe. The cost of IFB to to do this would be about $12-15.

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            • #7
              Re: Heat loss through exposed floor at front problem?

              Originally posted by GianniFocaccia View Post
              If you re going through to the trouble of creating a heatbreak between the dome and entryway, you may want to slide a few IFB between the floor bricks and entryway bricks. Since they will be in direct contact, there will be some amount of heat transfer to exposed entryway bricks. How negligible this is, I don't know. I did it to be safe. The cost of IFB to to do this would be about $12-15.
              Thanks Gianni. What are IFB?

              Edit: insulating fire bricks I guess ?
              Last edited by di11on; 05-23-2014, 02:03 PM.
              My oven on a pallet build thread

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              • #8
                Re: Heat loss through exposed floor at front problem?

                Originally posted by GianniFocaccia View Post
                If you re going through to the trouble of creating a heatbreak between the dome and entryway, you may want to slide a few IFB between the floor bricks and entryway bricks. Since they will be in direct contact, there will be some amount of heat transfer to exposed entryway bricks. How negligible this is, I don't know. I did it to be safe. The cost of IFB to to do this would be about $12-15.
                The problem with IFB's is that they abrade really easily if they're anywhere exposed to oven tools etc. Some builders cover them with stainless in the area that gets plenty of wear.
                Kindled with zeal and fired with passion.

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                • #9
                  Re: Heat loss through exposed floor at front problem?

                  I'm thinking, as a compromise, a 10cm gap between oven floor and entry floor filled with ceramic blanket and covered with a thin layer of refractory mortar? If it degrades over time, I just re-mortar it?
                  My oven on a pallet build thread

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                  • #10
                    Re: Heat loss through exposed floor at front problem?

                    My error. I mistakenly assumed there would be some form of entryway cover, like stainless. David's words ring true - any kind of insulation needs to be kept away from abrading tools and pans, but more importantly, away from food.
                    Mortar would just crumble, and for that matter is not all that healthy to get into your food.

                    An option would be to taper the matching sides of the adjoining entryway and floor bricks to leave a 1/8" - 1/4" gap at the bottom. The top surfaces would connect tightly, but the taper would create minimum contact between the two.

                    Another solution (oft scrutinized) to reduce heat transfer contact between floor and entryway is a length of square stainless tubing.
                    Last edited by GianniFocaccia; 05-24-2014, 07:12 AM.

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                    • #11
                      Re: Heat loss through exposed floor at front problem?

                      Originally posted by di11on View Post
                      I'm thinking, as a compromise, a 10cm gap between oven floor and entry floor filled with ceramic blanket and covered with a thin layer of refractory mortar? If it degrades over time, I just re-mortar it?
                      Di11on,

                      I only have mine separated by a very narrow gap with two runs of 1" flat cf gasket material. The insulation is only about 3/16" thick. If my conversion chart is right that is only 4.76+ mmilimeters. The insulation stops about 1/4' from the floor surface. I let that fill in with ash. Just keeping the oven floor brick and the entry floor brick from touching yields a tremendous thermal break.
                      joe watson

                      "A year from now, you will wish that you had started today "

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                      • #12
                        Re: Heat loss through exposed floor at front problem?

                        Gulf, time to pick your brain a little. I am worried about water infilltration in the vent area. I have decided to put in a thermal break and eliminate the 2 in of ceramic board under my vent area fire brick. I would like to flash this area some how. What about a stainless metal pan that is the outside dimension of the vent, outside brick to outside brick, has a 90 degree turned up leg, say 2 1/2 in high, the same size leg at the back of the pan which butts the ovens outer brick and insulation. This pan would lay on the concrete slab and entry material would then be laid on top of the pan. The pan would be pitched positive to the outside with weepers to drain moisture away from the vent entrance area. Using a scratch coat of fireclay would accomplice this. give me your thoughts, Wayne

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                        • #13
                          Re: Heat loss through exposed floor at front problem?

                          Originally posted by Campmaki View Post
                          Gulf, time to pick your brain a little. I am worried about water infilltration in the vent area. I have decided to put in a thermal break and eliminate the 2 in of ceramic board under my vent area fire brick. I would like to flash this area some how. What about a stainless metal pan that is the outside dimension of the vent, outside brick to outside brick, has a 90 degree turned up leg, say 2 1/2 in high, the same size leg at the back of the pan which butts the ovens outer brick and insulation. This pan would lay on the concrete slab and entry material would then be laid on top of the pan. The pan would be pitched positive to the outside with weepers to drain moisture away from the vent entrance area. Using a scratch coat of fireclay would accomplice this. give me your thoughts, Wayne
                          Wayne,
                          You may be on to something there, but I will have to "stew" over that for at least another shift at work.

                          I continued my 2" of CalSil through the entry. But that was for only the floor brick. After the oven heat break, my entry brick set down on the vermiculite layer. Outside of that all my face brick set completely down on the concrete hearth. The only floor brick that I have mortared in is at the facebrick entry. I have a storm door that sits in this area when the oven is not in use. I also have a cover which projects out a few feet over the entry.
                          Flashing is not something that I am so sure of. What I would like to see, is for someone to encorporate a "brick ledge" in the structural hearth slab. For a "doggie house", this would not be to difficult. For an Igloo this would take precise planning. But in either case, it would solve a lot of water problems .
                          joe watson

                          "A year from now, you will wish that you had started today "

                          My Build
                          My Picasa Web Album

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