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Old 04-29-2008, 07:38 AM
70chevelle's Avatar
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Default Getting Started

Ok - Quick update and a few questions. First, I don't have any ability to change my dimensions or plans. I'm looking at how to get the best of what I have available to me. Here goes!

I've expanded my foundation to gain a little space, and have been working on a design that will work. I'm going to be able to get a 30" dome on my hearth. The hearth is going to be 48" wide by 51" deep. I had to do some creative engineering to get these dimensions, and have taken a few photos, and will document and post in the future. With this size hearth, I will be able to fit the 30" oven with a 6" overhang at the door and still have room at the rear for my 8" square terra-cotta flue for the fireplace. The flue for the fireplace will be built in to the hearth, open to the smoke chamber at the rear of the fireplace. The oven will also have an 8" flue at the entry way.

Since I'm in the planning stage of the oven, while I'm starting the fireplace, I have my semi-final design.

I plan on using 2" of FB board below my oven floor, which will be low duty fire brick set on edge.
Question: I've seen where some have laid the walls on the cooking floor, and others have laid the walls on the hearth and left a gap for expansion and contraction. My plan would be to lay them on the cooking floor to ensure that the insulated cooking area is totally encapsulated. Good thought?
Question: Is 2" of FB board without vermiculite/concrete below enough for insulation? By the way, I plan on using brick (solid, but not firebrick) for my hearth, not concrete, if that matters.


Dimensions: 30" diameter, 13.5" dome height, 8.5" x 18" door opening.

Insulation: I will cover the dome with refractory mortar, then 2"-3" of FB blanket, then fill the balance with vermiculite. The brick enclosure should allow for an additional 1" on the sides and 3"+ inches on top. All in all I'll have 2" FB Board, firebrick on edge for the floor, and 3"-6" of FB Blanket & vermiclite on top of the firebrick and refractory mortar.

Within the confines of my dimensions and design, should I be able to cook some pizza's?
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Old 04-29-2008, 08:15 AM
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Default Re: Getting Started

Sounds good to me. The bricks-on-edge may be a little overkill. Experience has shown that brick laid flat have sufficient thermal mass.

I'm a little concerned about the fireplace vent at the back of that 51 inch slab. Your fireplace faces forward, right? Outdoor fireplaces sometimes have draw issues without a couple of feet of horizontal run just above the firebox.
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Old 04-29-2008, 09:23 AM
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Default Re: Getting Started

I think??? I have that worked out to some extent. My plan for the fireplace is to create a smoke chamber behind the firebox. The sides of the firebox are going to angle from front to back. Should look like this "\_/" if up is the front. The rear of the firebox will angle towards the front of the fireplace, from bottom to top, "/". I'm going to leave an airspace between the bottom of the hearth and the rear wall of the firebox, "|/". The hot air will hopefully rise, and end up in the smoke chamber behind the rear of the firebox, and then between the heat and the draw go up the chimney. At least that's the beginning of the plan for now.

ps - per my current design the center of the chimney will be approx 44" from the front of the fireplace.
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Old 04-29-2008, 10:16 AM
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Default Re: Getting Started

I love the idea of the firebricks laid on their sides for the oven floor. Considering that a lot of people have difficulties maintaining a hot floor, I think the extra mass is nice insurance will not greatly increase your fuel consumption compared to flat laid bricks.
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Old 04-29-2008, 11:13 AM
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Default Re: Getting Started

If you are going to mostly pizza, I would agree with DMUN and go with bricks lying flat. My thermocouples show the floor is the slowest to heat up and lying them sideways may increase your firing time more than a little.

Anyone with side floor bricks have any experience to report?
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Old 04-29-2008, 11:19 AM
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Default Re: Getting Started

Quote:
Originally Posted by wlively View Post
If you are going to mostly pizza, I would agree with DMUN and go with bricks lying flat. My thermocouples show the floor is the slowest to heat up and lying them sideways may increase your firing time more than a little.
I would agree.
It's hard enough getting heat to saturate the floor when the bricks are laid flat.
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Old 04-29-2008, 11:32 AM
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Default Re: Getting Started

The amount of information makes my head spin. I'll tell you what I've read on here and other forums. Thinner floor will heat quicker, but cool faster. Thicker floor will take longer to heat, but retain the heat longer. For pizza's, it seems that the floor temp is very important, especially at higher temps (800+) and you don't want your floor temp coming down as your cooking. So which one is more efficient? Would you use more fuel for the longer heat up, and then longer cool down, or more fuel to keep your temps where you want them while you're cooking? Anyone?
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Old 04-29-2008, 12:16 PM
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Default Re: Getting Started

As a historical note: Pompeii oven building arose from frustration with the massive Scott style barrel vault ovens. When I joined the forum in the summer of 2005, the style was to put the vermiculite layer under the support slab. This didn't heat up at all well. Then there was a brief period of putting a second layer of brick under the floor, or just a slug of concrete there, buried in the insulation. This was called the island hearth. At least this left the floor insulated, but it still too too long to heat up. Finally, the idea of extra mass under the floor was abandoned, and makers (myself included) just put a single layer of flat bricks directly on the insulation.

The way to keep the floor hot is to keep a fire with flame licking up the dome of the oven. The produces a lot of heat, and it recharges the floor between pizzas. Commercial ovens have thicker floors (and thicker domes) but they use bigger fires, and they never fully cool down.
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Old 04-29-2008, 12:59 PM
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Default Re: Getting Started

Quote:
Originally Posted by dmun View Post
.... Commercial ovens have thicker floors (and thicker domes) but they use bigger fires, and they never fully cool down.
I could add one thing. Commercial ovens are thicker, but not a lot thicker. If a residential pre-made oven is about 2 1/2-3", and a Pompeii Oven using half firebricks if 4"-4 1/2" thick, a professionally made commercial pizza oven is about 4"-5" in the dome and 4" on the floor.

James
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Old 04-29-2008, 01:29 PM
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Default Re: Getting Started

I would not change my flat floor. I have cooked 10 pizzas without issue or much additional wood. For my usual family bakes, once the dome is white, I simply push the fire to the back of the oven and that is fine for at least 5-6. We are talking large 16" pizzas here. If I am doing more I add a 3-4" dia log or two after pushing the fire back. I have never had to add any more than that.




Quote:
Originally Posted by 70chevelle View Post
The amount of information makes my head spin. I'll tell you what I've read on here and other forums. Thinner floor will heat quicker, but cool faster. Thicker floor will take longer to heat, but retain the heat longer. For pizza's, it seems that the floor temp is very important, especially at higher temps (800+) and you don't want your floor temp coming down as your cooking. So which one is more efficient? Would you use more fuel for the longer heat up, and then longer cool down, or more fuel to keep your temps where you want them while you're cooking? Anyone?
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