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Insulation Really Matters - Forno Bravo Forum: The Wood-Fired Oven Community

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Insulation Really Matters

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  • Insulation Really Matters

    Here's an educational experience. We were contacted a while back by the owner of an Italian-made pre-assembled commerical pizza oven at a restaurant. I won't mention the product name, though I know the brand.

    While the oven was fired, the top of the oven and the bottom of the oven enclosure were too hot to touch. The oven was venting a huge amount of heat through the top and bottom. This was causing a number of problems. In addition to burning too much wood, heating up the kitchen, and making it harder to keep the oven at high heat for pizza, the chef was trying to bake enough bread each morning to serve the restaurant, and the oven wasn't holding enough heat to get it done. Which really should not be the case.

    After some talking, we agreed they would open the top of the oven enclosure, and without risking damaging the oven chamber, removed some of the castable insulation. They added a couple of layers of Insulfrax, and for good measure a little vermiculite above that.

    I just heard back, and he writes:

    "It makes a dramatic difference. It's amazing. Please tell james, as i've been speaking with him about it and i know he's curious to know the results."

    Now, he's going to attach a layer of Super Isol to the bottom of the hearth. My guess is that it is going to get that much better. I think the oven uses less expensive castable expanded clay for insulation, and it just isn't up to the task. We have easy access to space-age insulators, and it's really worth going the extra little bit to make your oven work better.

    This was a greal real-world experiment.

    They make mistakes so you don't have to.
    Pizza Ovens
    Outdoor Fireplaces

  • #2
    Using Insulfrax

    James:
    I made an earlier post looking for info on how to use insulfrax, but since you brought it up here.......
    I found a pic from KiwiPete showing anchors in the hearth that he strapped chix wire to after sheathing the insulfrax, but was hoping for a second source. My q's are:
    1. How do you attach it to the dome?
    2. How do you attach it to another layer of insulfrax?
    3. How do you attach the insulating concrete to insulfrax?
    4. If you were to actually use five layers (just going by a post you made earlier showing the ability of insulfrax. I'm thinking 3 layers)of insulfrax, can you/how would you attach a stucco layer? Too fragile if you banged into without a more solid surface undeneath?
    5. Is there a min. recomended thickness of vermiculate on top of the blanket before you stucco?

    Sorry all for so many questions. Thanks for thinking about them.

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    • #3
      Using Insulfrax

      Hi CAM,

      Insufrax is very easy to work with. You just overlap the edges by 2" to make sure you have good coverage. You can hold it in place with chicken wire, which you can attach to the hearth. Basically, it just lays there and works.

      The same logic holds true for two layers. Cover the dome with two layers, making sure you overlap the joints, and don't line the joints up (for efficiency). This part isn't rocket science.

      You then just add your castable vermiculite/portland mix right on top of the Insulfrax.

      There are couple of ways of approaching Insulation. As many have noted, there is not such things as too much insulation, so if you have the space and budget, go for it. In general, I think 1" Insulfrax and 4" Vermiculite does the trick. If you have a whole box of Insulfrax, just use all of it. 1" of Insulfrax basically replaces 2" of vermiculite -- which you can do to help make your oven stand a little smaller.

      If you are building an Igloo, the outer shell, or walls, of the Igloo provide your structural rigidity. They are hard to the touch (go tap, tap) and hold out water. The inner insulation layers are not part of the hard outer shell. In fact, there is one method of building the Iglool, where you wrap the oven in Insulfrax, then build the Igloo shell with stucco and stucco lathe (leaving a window) and pour loose vermiculite into the gap between the oven and Igloo walls.

      Hope this helps.
      James
      Pizza Ovens
      Outdoor Fireplaces

      Comment


      • #4
        Aha!

        My basic thoughts were correct. I sure needed confirmation though. I didn't realize stucco and chix wire were that rigid. The hollow igloo trick sounds interesting, but I don't have the room. I'm thinking 3 layers of insulfrax and stucco would be nice and thin. If I have the room, 2 layers with some vermiculite will be a little cheaper I guess. Just have to figure which porch would like a pizza oven. Thanks James.

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