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Old 04-21-2011, 09:31 AM
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Location: Tucson, Az, USA
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Default Insulation Substitutes

Hey All, I have an insulation question. My pizza oven consists of 2-a fire arches, double fire brick sides, single walled front and back and a refractory encased clay flue liner. I have a box of 1" ceramic fiber blanket that will allow me to line the dome at least twice and the rest of oven at least once. Now, can I stuff the rest of the space inside the steel, cement board and stucco shell with unfaced fiberglass insulation? A lot of materials are hard to find in my area, mineral wool being one of them. I am a little concerned of the weight on my arched roof. The 2-a arch bricks, being the only available around, forced me to include a few straight bricks to widen the arch a little so I was hoping to go light. The weight of the encasement of the horizontal flue has put more weight on arch than I care for. Any advice is greatly appreciated. Thanks
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Old 04-21-2011, 10:25 AM
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Default Re: Insulation Substitutes

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can I stuff the rest of the space inside the steel, cement board and stucco shell with unfaced fiberglass insulation?
Domestic fiberglass insulation has organic binders that scorch and stink if exposed to greater than attic heat. If you're convinced that your two inches of refractory blanket (which is the minimum recommendation) will never let any heat out, you could use it, but you'd be a lot safer with vermiculite. It would be a lot easier to fill your cavities with it, as well.

What did you use to insulate under the floor?
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Old 04-21-2011, 03:30 PM
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Default Re: Insulation Substitutes

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Originally Posted by davidL View Post
has put more weight on arch than I care for. Any advice is greatly appreciated. Thanks
Some pictures always help, an arch properly constructed should hold tons of weight.
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Old 04-21-2011, 07:03 PM
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Default Re: Insulation Substitutes

Hello davidL,

I see you are in Tucson. Here's what I'd do. Perlite is easily obtainable from Simplot Partners in Phoenix. When I was there three weeks ago they were shipping five large bags to an oven build in your city. Perlite is about half the cost of vermuculite (at Simplot) and has a little better insulating value. It handles easily and fills all the nooks and crannies. I used wedges of Hardybacker and aluminum window screen to keep the perlite from places that didn't add R value, that way I didn't need so much.

You might also find both vermiculite and perlite at a landscapers supply store in Tucson. Golf courses, landscapers and nurseries are big users of these materials. Got any golf courses or landscapers in Tucson? Yes, you do !!!!

I agree with Dmun about using fg home insulation. If you use it at all then restrict its use to those areas of your build that don't get hot enough to heat up the organic binders. I've used mineral wool to block off between steel studs and corners of my enclosure so those areas wouldn't fill up with perlite. Otherwise, you can simply block off useless areas with noncombustible materials like screen or cement board. I had some black iron wire left over from tying re-bar and used it to fasten the screen and boards in position. Best of luck with your project.

Cheers,
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Old 04-22-2011, 08:18 AM
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Default Re: Insulation Substitutes

Depending on you enclosure detail you may also consider using a weak (12:1) perlite/cement mixture. This will hold it in place and prevent loose perlite from leaking or blowing out your enclosure vents.

You enclosure should, of course, be well vented.
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Old 04-23-2011, 04:41 PM
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Default Re: Insulation Substitutes

Thanks for the responses. I started to call some local nurseries and so it turns out they are my local source for perlite. It may be a little expensive in the quantities they stock but add fuel costs to picking it up elsewhere and I'll call it even.
I have kept a small fire in the oven for 8 hours today, temps on inside dome 425-475 all day. Outside of dome, uninsulated, near flue climbed to 225 but it took a long time to get that high. No other part on exterior oven wall even close to that.
The oven floor is full thickness fire brick with a product called "M Board", 1" thick under it. Some heat has transferred down, just over 100 degrees under my hearth slab after eight hours.
So long story short, ceramic blanket, 2" thick, especially on dome surrounded by perlite, and vented. Thanks Neil, PizzaNut, DMun and Brickie
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Old 04-23-2011, 05:37 PM
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Default Re: Insulation Substitutes

davidL,

Glad to be of help.

Landscape suppliers sell larger bags of perlite at lower cost.

I'd sure like to see more insulation under the hearth but giving up some heat to the slab may be acceptable in the long run. As your oven dries out it will operate more efficiently ....trade-offs.

I don't know what you have planned for vents. I have four 3" round vents obtained from Home Depot placed near the top of the side walls. The roof is slotted to allow venting under the ridge cap. I drilled through the stucco and cement board sides with a can shaped, carbide grit coated, hole drill, available from Harbor Freight in a six piece kit for $19.00. Installation was an easy press fit. There are other venting methods...if you plan ahead.

Cheers,
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Old 04-24-2011, 07:26 AM
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Default Re: Insulation Substitutes

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100 degrees under my hearth slab after eight hours
That's not bad, my slab is warm to the touch the next morning with two and a half inches of insblock19.
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