I am posting this in both places -- here and fornobravo/forum, where
we will make it sticky.
Using a ceramic insulating blanket is a good idea, for both brick
ovens and refractory ovens, because they are efficient, don't use a
lot of space, and keep loose insulation from ever getting into your
oven. And they aren't that expensive. Would folks agree with that?
Unless budget is a serious issue, you should consider using it. (We
include a large 6#, 1" blanket as part of our refractory ovens.)
If you are looking for a place to buy a ceramic insulating blanket,
contact email@example.com. They are in Atlanta, and
ship UPS. Tell them to give you the price for Forno Bravo customers.
If you find a better source, or a good regional source, let us know.
Try this E-bay seller.* He is in*Portland *He has some interesting stuff*regarding refractory materials and blankets
o.k., i am sold on using a insulating blanket, but how much
pumice/vermiculate insulation can we save that way ?(what would be the
ratio, e.g 1inch insulation blanket equals 3 inches of vermiculate as
i really would like to have a super insulated oven, yet like to get
down in thickness..., since i also like to have as much space on the
side of the dome for putting things down while using the oven.
The rule of thumb is 1" blanket and 4" vermiculite. 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.
I agree that you want the oven well-insulated, but think that you have some wiggle room. My oven here has 1" of low-tech blanket insulation (I don't even know the name of it, but it can't be close to Insulfrax in efficiency), and 2-3" of vermiculite, and I have never felt heat in my stucco walls. This is an extreme example -- I did it intentionally to see how it would work, and I think we can take a small lesson from the experiment.
Long answer to a short question -- but some interesting background info.
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