6# vs. 8# insulation

[philiph4@ameritech.net]

Re: 6# vs. 8# insulation

I am planning an igloo style oven using 8# Kaowool blanket only with Chicken wire and stucco on top. How many inches of insulation do I need? The pompei oven ebook says 2 to 3 inches. Is this enough?

[kebwi]

Re: 6# vs. 8# insulation

I'm a newbie here, so my advice is worth only the degree of pompousness I convey through my writing. However, the wisdom I am gathering from the FB community is that the "right" amount of insulation is the amount you are willing to pay for, have physical space for within your hearth bounds, and have the patience to go to the trouble of installing.

I do believe 2 to 4 inches of 8# blanket is considered acceptable by the FB community. I'm sure someone else will chime in.

[ThisOldGarageNJ]

Re: 6# vs. 8# insulation

My thoughts, The amount of insulation is based on final plans for your oven,,
If your only cooking pizza, minimal insulation is enough...
If you want to roast a pig,,,,You want more heat retention and holding temps and mass.
If you want to bake bread,,,, You want a lot of thermal mass
I can only add that I thought I only wanted to cook pizza, then I found out I could cook bread, chicken, steak, etc.... My point is dont cut yourself short now,,, Your not talking about theat much more expense and in the long run you will be able to leave a pork loin in the oven slow roasting overnight after you finish cooking your pizza's

Mark

[lwood]

Re: 6# vs. 8# insulation

That's great advice Mark, insulating to the nth degree is not the only design parameter to be considered. Since i haven't even reached this step in my build, i have become an expert on the subject. Ha ha. But Mark makes an excellent point that maybe you want to give up a little insulating R value for the thermal mass that you gain especially in a confined space. What i have found out in my quest for alternatives to the rock wool you all talk about.......is that perlcrete is an excellent insulator. As a matter of fact, even unexpanded perlcrete is an excellent insulator. Out of necessity, I will be doing a solid unexpaned perlcrete shell, probably 5-6 inches thick, because the rock wool is just not available here in the provincial Philippines. The difference in the thermal conductivity (K) of the the expanded vs unexpanded perlite is very small and orders of magnitude smaller than most other solid rock materials because of it's honeycomb-like physical structure.

I think you all should be using K rather than R-value. Have you ever seen units on an R-value? Never, I don't have my CRC sitting next to me but K definitely has units.

Since you are compressing the the rock wool, it seems to be approaching the the pure thermal conductivity K of the ceramics in the wool and the perlcrete. The wool just provides an airspace. So, you are exchanging thermal mass for insulating value. Depending on how you want to use your oven and how important wood conservation is to you should determine how much insulation to use. If you really are concerned about wood consumption you should make the biggest airspace you can with the rock wool. Actually here, firewood is not a problem, typhoons provide more firewood than I could use in a lifetime. And roasting a whole pig is something I want to do in my oven. So, my thinking is that my 5-6 inches of perlcrete should be ok. We shall see when I fire it up.

[vintagemx0]

Re: 6# vs. 8# insulation

Just as a side note, R is the reciprocal of K. That is R = 1/K, and K = 1/R. I work with products that require thermal insulation protection and the useful value we use is K.

[lwood]

Re: 6# vs. 8# insulation

Just as a side note, R is the reciprocal of K. That is R = 1/K, and K = 1/R. I work with products that require thermal insulation protection and the useful value we use is K.

I agree, I can think about it easier in terms of K, thermal conductivity. Thermal conductivity is how well the material conducts heat. The smaller the K the better the insulator.

By the way, here is what wikp has to say about it:
* thermal conductance = k/A, measured in W?K−1?m−2;
* thermal resistance (R value) = t/k, measured in K?m??W−1;
* thermal transmittance (U value) = 1/(Σ(t/k)) + convection + radiation, measured in W?K−1?m−2.