Insulating dome with Insulfrax only - but how much?
I plan to build my oven on a metal stand so that I could potentially move it to a different location in my back yard in case I decide to build addition to my house or change layout of my deck.
Because of that I decided to go with 4" of Insulfrax alone as insulation on top of the dome. The goal is to minimize weight primarily. I have not yet decided if I would go with sheet metal enclosure or wire/stucco over Insulfrax. I have not done the math yet, but thin enoguh sheet metal seems to be lighter than stucco and it will not crack if oven is moved.
I did a search and have found in several posts that one box of 50 sq ft of Insulfrax should be enough to cover 42" oven. But posts do not specify how many layers you could do with that one box.
My oven will be 36" internal or about 42" external diameter and I am thinking about putting 4" of Insulfrax.
How much Insulfrax do I need to cover the oven with 4 one inch layers?
The calculation I did was (each layer of insulation enlarges surface area needed for the next layer):
Layer Diameter [in] Surface area [ft^2]
1. 42" 19.24 sq ft
2. 44" 21.11 sq ft
3. 46" 23.08 sq ft
4. 48" 25.13 sq ft
Total surface area is 88.56 sq ft, so it means two 50 sq ft boxes should be enough.
If I do the same calculation for standard 42" internal diameter with 4.5" thick walls - 51" diameter semi-sphere, surface area is then 28.37 sq ft. (or 127.43
sq ft for all 4 layers combined - three 50 sq ft boxes)
But this calculation does not account for overlaps and creases - will need more surface area in reality. It also assumes the oven shape is semi-spere. The actual shape will be flatter - will need less surface area in reality.
Since this is all theory, I need some practical advice on actual amounts of insulation blanket used.
I think you're on target - two boxes will do it.
My oven is about the same size as yours (35" inside; 43" outside) and a single box of insulfrax covers it nicely; in most places, twice or even three times.
Use up every square inch of the stuff. You can't put too much on. It's actually pretty easy to work with - docile, easy to form and sticks to itself.
One piece of advice on cutting it: I found a LONG set of scissors did it nicely. Failing that, saw it carefully with a long carving knife. It will dull the blade of the knife, so make sure it's not a good piece of cutlery.
Do NOT use a cheap "never needs sharpening" knife.
It will develop natural folds which you should cut and overlap. The pix should explain how to do it better than my words.
Thank you very much for tips and great pictures. I think that they show the procedure so good that they should be incorporated in the oven building pages.
I have ordered two boxes.
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