Blanket Insulation

[david s]

I’ve used rock wool blanket on a few oven builds. For the same thickness the rock wool was slightly cheaper and only marginally inferior as an insulator. It is however even more water absorbent than the ceramic fibre blanket and it’s worst quality I found was its consistency. It is much softer than ceramic fibre making it more difficult to cut and harder to work over with the vermicrete layer. I much prefer and use exclusively now, the ceramic fibre blanket. I think it’s well worth the additional cost. If you go the ceramic fibre blanket route, just check to make sure you get the bio absorbent carcinogen exonerated blanket. Think twice about using foil in any layer over the dome because as well as acting as a slip layer it will also act to trap moisture from escaping, making drying the oven that much more difficult.

[Drooh]

Hi there, I used about 3" thick of this fiberglass insulation between my stainless steel walls, hopefully it's going to be ok.

Insulation Type	Sheet/Strip
Thickness	2"
Width	24"
Length	8 ft.
Temperature Range	0° to 1000° F
R Value	7.7
Heat Flow Rate	0.26 @ 75° F
Density	2.4 lbs./cu. ft.
Material	Fiberglass
Flexibility	Flexible
Backing Type	Plain
Color	Gray
For Use Outdoors	No
Specifications Met	ASTM E84 25/50 for Flame and Smoke
Additional Specifications	SDS

Whether it's for industrial furnaces or other extreme-heat applications, these lightweight fiberglass sheets can handle temperatures up to 1000° F. Material meets ASTM E84 25/50 for flame and smoke. They can be used outdoors with metal jacketing (sold separately).

[fox]

Hi, I used 4" of ceramic insulation (2 x 2") & in the summer I cant feel any heat radiating through the dome but in the winter the dome feels a little warm. So I would say 4" is a good amount.
Re Rock wool, I think it might nor reach the temperature requirements if it is placed directly on the inner dome but might be ok as a second layer?

[SimonMALTA]

Hi I was looking for the blanket locally but was offered rock wool usually used in dry wall is that what you are referring to above is it safe and effective insulator?

[captkingdom]

Re: Blanket Insulation

I used 12" of Roxul blanket, which is a mineral or rock wool product.
It is working great. I also put down 3 layers of aluminum foil first as a radiant heat barrier. I did not use a Portland product for mortar which some have said would corrode the foil. I suspect though that even for those who do multiple layers would work fine.

[redmen4]

Re: Blanket Insulation

I am also building an igloo style oven. I am planning on 3 inches of blanket insulation, with no additional insulation. On to p of the insulation will go my stucco. I have researched what you are asking on the site. I do remember that the consensus was 3 inches of blanket insulation was more then sufficient.

Jim

[philiph4@ameritech.net]

Re: Blanket Insulation

I am still struggling with how much insulation is required. I have purchases 8# kaowool 1" blanket. I am planning an igloo style oven and don't want spend more on insulation than necessary. Opinions seem to be all over the board. I want to have a fully functioning (not only for pizza) oven. Is 2" enough or do I need more? I have a lot invested already and i certainly don't want to skimp here but I also don't want to spend more than I need to. Is there an official FB opinion?

[james]

Re: Blanket Insulation

Insulation not rated to pizza oven temperatures can also scorch. It puts out a black sooty smoke and smell that's pretty awful.
James

[dmun]

Re: Blanket Insulation

Acoustical batts are basically domestic insulation without the vapor barrier. It's not nearly dense enough to provide proper refractory insulation.

If you don't want to spring for the refractory blanket insulation, just use lots and lots of vermiculite or perlite concrete.

[quiltman]

Re: Blanket Insulation

Quick question about Mineral Wool. I have found a supplier of Roxul AFB Mineral wool which will supply batting material for $40 for 6 sheets of 24" x 48" X 2". Although they specify the material as Acoustic damping and fire resistant, they do not mention insulative properties. Is all Mineral wool the same or can there be huge fluctuations in insulative properties?
-John

[altamont]

Re: Blanket Insulation

Heat can only be transferred several ways: Conduction, convection, radiation

If any one (or more) of those are reduced in any way there is less heat loss. Insulating layers do this in a variety of ways.

Take an old-fashioned vacuum thermos bottle for example. These are nothing more than a container welded inside another one at the rim. The secret to their keeping things hot or cold is that almost all of the air between the two containers is removed (hence the 'vacuum' in the name). That reduces the convection part of moving heat (gas transferring heat).

Conduction of heat can be thought of as a function of the density of a material. A block of metal will conduct heat much faster than a wad of feathers (why goose-down feather quilts are so popular during cold and snowy nights). Porosity, air-entrapment, interrupting radiation, etc. all come into play here.

But heat transfer in all of its complexity boils down to conduction, convection and radiation. Interrupt those and you burn your fingers less and less.

[altamont]

Re: Blanket Insulation

Regarding exposure to ceramic fiber - relax. "Don't Panic" (as you can tell, I really enjoyed Douglas Adam's 'Hitchiker's Guide to the Galaxy'). Because the fiber is totally enclosed there is no exposure so it is safe.

This material (ceramic fiber) is not a hazard like asbestos - it is very safe. The major health concerns arise after extended periods of time at 'elevated temperatures'. When ceramic fiber is behind the firebrick it never really gets a chance to even be exposed to the temperatures required. Furthermore, the dangerous change (the conversion to the crystobalite form of silica) at ELEVATED temperatures is very gradual and 'slight' - just a small portion gets converted. Seeing how the insulation in wood-fired ovens never get that hot ... well, it wouldn't be an issue.

Regarding if Mineral Wool and Ceramic Fiber are the same thing: They are if you generalize similarities such as "fiberglass insulation is the same as ceramic fiber" - they perform what we want the same way (insulate by reducing the conduction of heat from a hot face to a cold face by reducing the density of the layer, lowering the thermal conductivity and thermal radiation, etc...). The primary difference is the raw materials (resulting in a different composition, yada, yada, yada), cost of forming, binders used, ....).

I guess we could look at this differently:
- I need a car to get me from point A to point B.
- I could use a good old 1972 VW bug ... or a nice Mercedes (any model & year).
- I have to pay for it out of my own pocket.
Which one is a personal decision. However, both will accomplish what I want. And my experience indicates that the mineral wool would be not only cheaper but provide a little more insulation per inch thickness.
The one drawback is I will probably be using mineral wool board. It is stiff (but cuts very easily with a knife or drywall saw blade (hand powered course saw). It does not conform to a curve. So that means that I will be cutting the board up and/or 'curfing' it to fit. Ceramic fiber blanket is easy and faster to work with.
My labor costs me ... time. If I were paying someone, I would have to sit down and figure out what I would be willing to pay extra for a skilled worker to hassle with the board versus throwing a more expensive blanket over the top.

=========

I want to point out here that manufacturers of furnaces take these things into account as well as having to make assumptions about the skill levels of the people that install or repair their products.
I have a skill level and understanding based on years of experience.
But how about some person purchasing an oven kit that has never been around a furnace before? For these reasons companies, like FB, will go the extra mile and provide easier to work with materials that might cost more but are easier to work in their kits and maintain a very high level of safety.

I don't have anything to gain or loose here but thought that I should point out that I only initiated this conversation to point out an alternate insulating material that might make it easier to source than other materials mentioned.

[Frances]

Re: Blanket Insulation

Minral wool and rock wool - is that the same kind of product?

In any case, this post makes me feel a lot better about the insulation I used. Although my oven works beautifully, I've still always had this sneaky feeling that it might have been even better with the FB blanket... but maybe not after all.

The guy who sold me the stuff said much the same as you have here, but its nice to have it confirmed (by someone who isn't trying to sell me something ).

[captkingdom]

Re: Blanket Insulation

Wow Thanks Altamont!
I have also heard that one wants to encapsulate ceramic fiber to prevent exposure.
Will the board hold up under the hearth?
I am very excited to have a "next generation" Pompeii oven ASAP

[james]

Re: Blanket Insulation

Welcome aboard Altamont,

As Drew says, we can always use a few more experts here. :-)

Your comment on ceramic fibers is well noted, but I have a question. The Pompeii oven design calls for a layer of ceramic insulation full enclosed outside of the oven chamber and held in by the oven enclosure itself. I definitely would not want extended exposure to ceramic fiber, but isn't it OK as it is enclosed?

Have fun with your project -- we're looking forward to seeing you progress.
James