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-   -   Barrel Vault Question (http://www.fornobravo.com/forum/f9/barrel-vault-question-4405.html)

70chevelle 06-27-2008 08:35 AM

Barrel Vault Question
 
After reading thru the primers & stickies, etc, I understand the passion of the pompeii oven on this sight as it pertains to making pizza's. I'm just looking for a little clarification, as I'm a little analytical.

1) The pompeii oven reflects heat better due to its dome construction as compared to the square rear corners where the arches meet the rear wall.
2) The pompeii oven is constructed in such a way that it's wall thickness is thinner than a traditional barrel vault (4.5" compared to 10" respectively). This translates to less thermal mass for the pompeii, which means quicker heat up time.
3) The pompeii oven is to be heavily insulated so that it can retain the heat, where the barrel vault loses it's heat slowly due to the higher thermal mass

Those are the three main differences that I could find here and on other sights.

My question:

If you were to build a barrel vault using the pompeii principals, (ie: 3"-4.5" wall thickness with the same amount of exterior insulation, same dome height, etc.) should it not have similar heat up and retention as a pompeii oven?


Any thoughts?

dmun 06-27-2008 09:13 AM

Re: Barrel Vault Question
 
Every oven should be insulated, top and bottom, high mass or low. You're just throwing money away if you don't.

There are structural reasons apart from thermal mass why barrel vault ovens have thick walls. The arch is just more stable than vertical walls with an arched roof.

It all boils down to the pizza/bread question: The round oven is just better suited to fire in the oven cooking: you have room for the fire on the side, with the fire there you don't have to guess about how the hot edge of your pizza is browning up.

The barrel vault is more suited to making multiple batches of retained-heat baked breads.

Mojoe 06-27-2008 07:58 PM

Re: Barrel Vault Question
 
Brick wall thickness is the same, whether its a 9" long brick cut in half or the same 9" long brick (which is typically 4.5" wide) standing on end (soldier) or laying flat on its 4.5" wide surface. The cooking floor bricks are typically standing on the thin side (2.5") which makes the firebrick cooking floor 4.5" deep as opposed to laying them flat on the wide 4.5" side making the firebrick cooking floor depth 2.5".

My vault has 3" of Inswool HP blanket (2300F rating) and 2" inches of vermiculite. I'll hit over 900F in about 2 hours and after raking the coals out and putting a door on the temperatures are over 600F the next morning. The door was nothing fancy, 3, 4" thick hardwood rough sawn stock nailed together.

I say "was" because I burned it up cooking a 16lb turkey Thanksgiving Day last year. I fear my new door is going to weigh near 50lbs, anyone have a winch or chainfall for sale?

berryst 06-29-2008 09:45 PM

Re: Barrel Vault Question
 
go check out traditionaloven.com for an alternate view point
berryst.

70chevelle 06-30-2008 04:06 AM

Re: Barrel Vault Question
 
Mojoe - You can also go with a lower thermal mass and lay the bricks on the short edge, giving you a 2.5" thickness.

What are your interior dimensions and dome height?

Berryst - doesn't really answer the question:

"If you were to build a barrel vault using the pompeii principals, (ie: 3"-4.5" wall thickness with the same amount of exterior insulation, same dome height, etc.) should it not have similar heat up and retention as a pompeii oven?"

Or another way to ask the same question, which has more to do with heat up times, the amount of thermal mass or the shape of the oven? And,

which has more to do with heat retention, the amount of insulation or the shape of the oven?

The assumptions would be comparing 2 ovens that have the same interior area & dome hieght.

Mojoe 06-30-2008 06:39 AM

Re: Barrel Vault Question
 
Internally the oven is 32.5" wide by 40.5 long with a dome height around 18".

I don't see why you couldn't lay the cooking floor bricks flat as in the Pompeii but I seriously doubt laying the sidewall bricks on edge could sufficiently support the arches. You might also be able to switch the order of your slabs which may yield faster heat up, structural on the bottom, then insulating, then your floor bricks. This is how I made my oven but the "insulating slab" has a higher cement content so it is not as efficient at holding the heat as the proven insulating slab mix design. I haven't really given my oven a true heat up test as last year I was burning green wood with an ambient temperature in the low 60's, this year will tell the tale.

If I had it do over again I would have compared the total brick weight of a pompeii with a barrel and made the insulating slab to the applicable proportions.

The main reason I went with a barrel is because I was intimidated by the pompeii, having never cut or laid a brick in my life. If I ever get the chance to build another oven it will be a pompeii as it is not as daunting a task as I assumed. I like my oven but I will never use it to its full potential.

berryst 06-30-2008 06:55 AM

Re: Barrel Vault Question
 
The way I see it the matter is somewhat simple yet complicated in the end

I have looked at both oven styles and have come to my own conclusions. This particular site seems to attract great passion for the round igloo oven. It is no doubt very strong, God knows I built enough igloos in my youth. You could walk on the top of em in the morning and they were hard to collapse.

Here the principal is simple physics. Heat plus mass is all you need. Look at the mud and straw jobs of early history. Reflected heat is a bonus. I am doing a combination of both ideas.

The barrel stove or really the arched stove as it should be called often has a square bottom. This is practical in bread making. The Igloo has dead space around the edges. you can stuff some coals there but nonetheless the space on the edges is not very useful as I see it. I am doing a true hybrid. A barrel shaped stove with an arch. There is no dead space and its easy bank coals at the far end. The heat is captured and the walls are as thick as you want. 10" is on the thick side and will take extra time to heat. I a doing a 4 inch wall with a couple of inches of cladding.

Addressing door opening and dome height is not an issue. The principal is the same in both designes. The door should be small enough to capture the heat and large enough to work. The 10 to 6 ratio of door to dome appears optimal

Finally these are my thoughts and why I am building the way I am. I am not an expert but I believe I have internalized the principal's. I like the look of the igloo pompeii but I also love the graceful tapered ends of the barrel


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