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james 08-22-2005 02:03 PM

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.



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.

paulages 08-22-2005 03:19 PM

ask him if it is possible to compare these figures to castable refractory insulation (in place of either the refrax blanket OR the vermiculite insulation. i would think the castable might perform similar to the blankets.

the closest figures i can contribute are:

roughly 1.5-2 inches of 2500deg F rated castable insulation reaches 120-140 deg.F when the interior is 700-950 for 2 -3 hours. (i know those are a lot of variables, but it at least gives us a ballpark idea of how well it functions).

james 08-22-2005 03:30 PM

I'll see if I can do that and get back.

The figures above are aftter 24 hours -- which is a more extreme test, so the insulation is more efficient at those thicknesses. Paul, are you going to add loose vermiculite around the dome still?


paulages 08-22-2005 04:07 PM

yes---whenever i get around to finishing the walls. i have a million projects going on right now...but i've found plenty of time to cook in it!

Versachi 08-07-2007 09:12 PM

Re: Insulation Efficiency
Just wondering if anyone has used fiberglass insulation around their dome? I wouldn't use it directly on the dome but if you had a layer of insulating blanket couldn't you use batts around your dome. The r-value would be much higher than perlite or vermiculite. I don't think temperature would be much of an issue since fiberglass is made at a higher temperature than we could fire the oven

arevalo53anos 08-08-2007 03:43 AM

Re: Insulation Efficiency

Yes, you could use fiberglass to isolation your dome.
Depending on cloth type, the blanket has different temperature capability. As lower as 150°C to higher 500°C.
You could use an inch of vermiculite/cement mixture and cover it with fiberglass blanket.
Search by Pizzabrasil and see oven pictures and better explanations about this matter.

Good luck


dmun 08-08-2007 03:56 AM

Re: Insulation Efficiency
If you use domestic fibreglass batts, be sure to strip off the paper vapor barrier, which is combustible.

RCLake 09-18-2007 03:11 PM

Re: Insulation Efficiency
I'm shopping for this in Dallas and I'm getting quotes on the blanket for 1" and 2" but also for 8 pound and 6 pound. I'm assuming the heavier is better but does anyone know by how much (i.e. 8/6 better

TDVT 03-17-2008 07:23 AM

Re: Insulation Efficiency
Since this thread was dredged up, I'll ask a question.

I have been taking in all the insulation conversations & I'm wondering about the FB blankets. I haven't actually seen it so I'm wondering how compressible it is, seeing how people are adding a hardcoat of vermiculite concrete/stucco to their oven over the blanket.

Wouldn't heavy-weight coating like that tend to compress the blanket, reducing it's efficiency?

CanuckJim 03-17-2008 09:13 AM

Re: Insulation Efficiency
TD, et al,

The vermic/cement mixture is quite light, really, so the blanket(s) don't compress significantly. I'd recommend 8 lb over 6 anytime.


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