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  • james
    started a topic Insulation Efficiency

    Insulation Efficiency

    I know that some folks are talking about getting the insulation right to keep heat inside the oven, and wood consumption down. This is true for both site built and FB precast ovens.

    We recommend a 1" Insulfrax insulating blanket (6#) and 4"-6" vermiculite or perlite as a general rule. Here are some simulated insulation numbers we had an engineer do a while back.

    James

    *******************

    I had an insulation engineer run a test, and conclude that the blanket replaces 2" of loose vermiculite. We had them run a simulation where they added 1" of insulfrax, and reduced 1" of vermiculite. 1":4", 2":3", etc. over a 24 hour 1000F exposure. The outer face tested consistently dropped by adding 1" more insulfrax and 1" less vermiculite.



    1" Insulfrax Blanket 6#, 4" Vermiculite 1000F** 172F

    2" Insulfrax Blanket 6#, 3" Vermiculite 1000F** 161F

    3" Insulfrax Blanket 6#, 2" Vermiculite 1000F** 151F

    4" Insulfrax Blanket 6#, 1" Vermiculite 1000F** 142F

    5" Insulfrax Blanket 6# ******* 1000F** 135F



    Thinking about it, I should ask him to add 1# insulfrax, and drop 3" of vermiculite and re-run the test. I would note that after 24 hours of 1000F, (which you will not approach), the outer face is barely warm.
    Last edited by james; 06-27-2006, 03:17 PM.

  • UtahBeehiver
    replied
    FYI,

    David S is from Townsville in Queensland so he is a great source for locating materials in Australia. KarangiDude and Oasiscm are from NSW and are also a good source for materials in that area.

    Leave a comment:


  • Gretsch
    replied
    Thanks David, all good. Plenty of timber and time on hand.

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  • david s
    replied
    Just remember that increasing thermal mass will increase fuel consumption and increasing floor or wall thickness increases heat up time. You may find the oven not that suitable for flashing up on a Friday night after work to cook two pizzas. Horses for courses as they say.

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  • Gretsch
    replied
    Originally posted by david s View Post

    If your oven is to be used primarily for bread, then as well as turning the insulating bricks on edge in order to increase the insulation layer thickness, you could consider turning the floor bricks on edge to increase the thickness and therefore the thermal mass of the oven floor.
    Yes pizzas and bread, but more importantly I want to capture every phase of heat decay right through to the end where I can dehydrate our crop of mangoes, bananas, tomatoes and whatever else we harvest in abundance.

    And yes I’ll turn both bricks on edge to increase the thermal mass and insulation.
    I also intend on using minimum of 75 mm insulation blanket followed with 50 mm vermicrete and clad the whole thing with bricks. Reckon that should contain the fusion within

    Leave a comment:


  • david s
    replied
    Originally posted by UtahBeehiver View Post
    Insulated fire brick is a suitable insulation under a firebrick hearth. K values for IFB runs about 0.15, CaSi board about 0.05. You may want to lay them on edge for more thermal thickness. Several Aussie builders have used IFB for their floor insulation.
    If your oven is to be used primarily for bread, then as well as turning the insulating bricks on edge in order to increase the insulation layer thickness, you could consider turning the floor bricks on edge to increase the thickness and therefore the thermal mass of the oven floor.
    Last edited by UtahBeehiver; 11-18-2017, 06:40 AM.

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  • UtahBeehiver
    replied
    Insulated fire brick is a suitable insulation under a firebrick hearth. K values for IFB runs about 0.15, CaSi board about 0.05. You may want to lay them on edge for more thermal thickness. Several Aussie builders have used IFB for their floor insulation.
    Last edited by UtahBeehiver; 11-18-2017, 06:40 AM.

    Leave a comment:


  • Gretsch
    replied
    Guday.

    I can get my hands on some light weight insulating bricks that were used in a kiln to fire up clay bricks and pavers. They’re the regular 230 x 115 x 75mm size. Seems like they’ll be an excellent insulation layer for the hearth, anyone know if they’re as good as the silicate board ? I want to retain as much heat in the floor as possible. Bread is on my cooking bucket list.

    Leave a comment:


  • kebwi
    replied
    Re: Insulation Efficiency

    Originally posted by FrankHawkins View Post
    What is perlite? And what is its difference to vermiculite? As I have bought vermiculite to do all of the outer dome with. Will it be ok to do it that way?
    Don't worry about it. It's very similar to vermiculite and used for similar purposes. I used it because I had a limited supply of vermiculite and could obtain perlite more easily when I ran out. Treat them as identical for the purpose of making insulating concrete.

    Leave a comment:


  • FrankHawkins
    replied
    Re: Insulation Efficiency

    What is perlite? And what is its difference to vermiculite? As I have bought vermiculite to do all of the outer dome with. Will it be ok to do it that way?

    Leave a comment:


  • kebwi
    replied
    Re: Insulation Efficiency

    Originally posted by FrankHawkins View Post
    Hi there guys. Searching through this thread but can't find what ratio mix people have used for the vermiculite concrete that you put around the insulation blanket around the dome?
    Is it purely just a vermiculite/cement mix?
    Also what method have people used to apply it onto the dome?
    According to my notes, I used 8: 1 vermiculite: portland around the lower third or half or so, then 4: 4: 1 vermiculite: perlite: portland for the next third or quarter or so, and then 5: 5: 1 for the top layer. I then hydrated it approximately 3: 1 mixture: water. There's pictures and videos somewhere in my account's albums, in my account's primary build discussion thread, and on my website (and on youtube):

    Brick Pizza Oven Models and Photos
    (Each picture has some notes below it, so expand the pictures at the vermicrete stage for details.)

    Leave a comment:


  • FrankHawkins
    replied
    Re: Insulation Efficiency

    Hi there guys. Searching through this thread but can't find what ratio mix people have used for the vermiculite concrete that you put around the insulation blanket around the dome?
    Is it purely just a vermiculite/cement mix?
    Also what method have people used to apply it onto the dome?

    Leave a comment:


  • cobblerdave
    replied
    Re: Insulation Efficiency

    Originally posted by stonecutter View Post
    Organic material is not a good idea.
    Gudday
    How very true, organics rot or burn either way they return to the carbon of which it was made. You can use this characteristic you you advantage though to make a low tec insulation.
    Chopped straw, rice husk, sugar cane mulch whatever and use enough watery clay to bind it will give you an insulating material. Even in the absence of oxygen the heat will break down the particles and if not it will break down over time anaerobic. It make an insulation that will go over an oven. If you pack it into glass jars and pack them together with something around to contain them it will be strong enough to support a small oven.
    Efficient ... No not really but better than nothing at all.
    But efficiency is what you think it is. A home oven is not really efficient as much of the heat is wasted. I'm guessing here but it would probably take 5 or 6 kg of wood for each kg of bread (food) cooked. It would be more efficient to keep it flashed up permanently and feed a number of households
    Anyway that's my take on that
    Regards dave

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  • stonecutter
    replied
    Re: Insulation Efficiency

    Organic material is not a good idea.

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  • josh_r
    replied
    Re: Insulation Efficiency

    Has anyone used dried rice as an insulator for the floor? filled a pot with rice and tossed it on the stove for about a half hour and it blackened the rice touching the pot, but about a half inch off the surface of the pot, the rice was barely warm, an inch off the pot wall, the rice was cool to the touch and was cool all the way through the center. Just an idea I had due to the fact that I have not seen vermiculite for sale here in Peru, but rice is as common as flies here.

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