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Post by patamos on Oct 22, 2014 15:35:00 GMT -8
So i have been finishing an oven with a 6" L-feed and 22" heat riser. Burns great. Only now the client i wanting it to be more of a pre-fired set up. I have set the exhaust port down low on the side to create a decent bell. This is working fine too, but i am wondering how thick to build the walls. Usually for fire-as-you-cook oven domes i have built about 1.5" of thermal cob and then 3 or 4 inches of clay-perlite. But in this case i am wondering how much thicker to make the walls for a long enough flywheel to roast for 3-4 hours. I've seen old school pre-fire set ups with 4+ walls, much hotter fires, and 8 or so hours of dwindling flywheel... So i am just wondering where the middle ground may be. Presently i am 2.5 inch thickness and thinking of leaving it at that.
Any and all thoughts are welcome
well being
pat
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Post by matthewwalker on Oct 22, 2014 15:56:23 GMT -8
Hmmmm, yeah, tough call. Too much mass and it will take a lot of energy to get it up to temp. I think your 2.5" thickness is a good compromise, if you insulate it well it should easily cook for the 3-4 hours you want. Mine is around 1.5" and does hold cooking temps for at least that long, if that helps at all.
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Post by patamos on Oct 22, 2014 19:30:15 GMT -8
Hi Matt,
Always good to hear your take on things.
It's probably closer to 2"+ with shrinkage so could be right on the mark.
Wondering also whether to work some ceramic felt into the insulation lay up or just go with a whole lot of clay perlite.
Any idea what 1/4" of felt compares to in cookie dough clay-perlite thickness? I'm taking a wild guess about 2".
Many thanks for your input.
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Post by matthewwalker on Oct 22, 2014 22:12:29 GMT -8
Well, I'd probably go with the clay/perlite since to my mind it's a hybrid between mass/insulation. I imagine it storing heat but with the heat moving through it more slowly than a denser material. The layers around my combustion cores seem to act that way, anyway. I would think that a hard break between the inner mass and outer insulation via ceramic felt might leave only the inner 2" dense material as a battery. I dunno, pure speculation there. Mine is the dense oven core surrounded by 4"-6" clay/perlite. I think if I really wanted to use the ceramic felt I'd put it on the outermost layer, trapping all the heat in the dual density cob structure.
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Post by satamax on Oct 23, 2014 14:57:29 GMT -8
Hello guys!
Well, just to say, pizza ovens have sand around the arch, so this insulates and stores heat. On the one i was using, i had about 1 ton or more.
Hth.
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Post by patamos on Oct 23, 2014 18:51:42 GMT -8
Hi Satamax,
Thanks for the perspective
Wow, that is a whole lot a mass! Definitely sends me towards Matt's suggestion of hybrid mass/insulation.
How big was the oven you were using? How big a fire for how long?
This is a 6" L-feed about 30" across at the base. 24" round deck.
I guess if anything i had best slightly over do it than under do it...
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Post by satamax on Oct 23, 2014 22:49:22 GMT -8
Hi Pat. Well, my father and grandmother had a pizzeria for three years, and i worked there. So i got acquainted with the oven. Floor of the oven was at about 1m10cm in height. It was a round 120cm with a vault. Front chimney. Ceiling about 40 to 50cm above that. May be a smidge more. I would burn wood in there for three or four hours at the time, starting about two hours before service. It's a fired oven, for the pizzas, obviously. When hot, it would remain hot for days. Tho, cooking temps were decreasing. May be an hour after the fire went down, yoiu wouldn't do a pizza anymore If that. Then you could bake bread or chicken for three or four hours The footpring was about 4 square metres, and above those 1m10 of the floor of the oven, all the sides and top of the oven were covered with sand up to the ceiling pretty much. I think the ceiling of the restaurant was at about 2m50. But for your problem, i'm thinking, have you read this? heatkit.com/docs/course.PDFIn the heat output calculation. Hth.
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Post by patamos on Oct 29, 2014 19:57:20 GMT -8
Thanks for the file Satamax.
I've seen that paper once before but gathered much new info on the second read. Still digesting the relevance of the various numbers....
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