#1  
Old 06-18-2012, 08:57 AM
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Default "Flat back wall" vs. dome/rounded shape

Hi guys-I'm currently reading "The Bread Builders" by Daniel Wing. In his oven design, he has a dome and entry similar to the pompei designs I've seen on this forum. But, he has a flat back wall. Is there any efficiency issues to this design? It seems the construction would be easier with a flat wall. Any insight would be appreciated.
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  #2  
Old 06-18-2012, 05:43 PM
Faith In Virginia's Avatar
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Default Re: "Flat back wall" vs. dome/rounded shape

Love that book myself. I even took a class at King Arther Flour that Daniel Wing taught. It was so cool.

I don't think there is much performance difference between the two ovens. The oven in that book is easier to build and requires less cuts of firebrick. I did find the book to have a few design Issues that I would not do myself like the way the oven is supported on nothing but re-bar. There are also many improvements that you can make to that design.

I will post more later but I need to run for now.
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Old 06-18-2012, 07:09 PM
Tscarborough's Avatar
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Default Re: "Flat back wall" vs. dome/rounded shape

That design is not that good, not because the overall shape but for the details. It was not designed by someone in construction.

The design criteria for a black oven, one in which the heat source is inside the oven, is pretty open:

A masonry mass designed for the intended purpose (i.e for multiple or commercial batches of bread 4-12", for sporadic home use 2-4").

The thermal mass should be discrete and isolated. That means that the interior masonry mass should be monolithic and isolated from the exterior as much as is feasible.

The masonry mass should be insulated to the highest degree feasible.

The inner door height of the oven should be 60-65 percent of the dome/vault height.

If wanted, the chimney should be at the front of the oven, outside the inner door, and should be sized at 10-15% of the door size, more for short stacks, less for tall stacks.

These guidelines apply for round, barrel, or square ovens.
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Old 06-19-2012, 07:59 AM
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Default Re: "Flat back wall" vs. dome/rounded shape

Quote:
Originally Posted by Tscarborough View Post
That design is not that good, not because the overall shape but for the details. It was not designed by someone in construction.

The design criteria for a black oven, one in which the heat source is inside the oven, is pretty open:

A masonry mass designed for the intended purpose (i.e for multiple or commercial batches of bread 4-12", for sporadic home use 2-4").

The thermal mass should be discrete and isolated. That means that the interior masonry mass should be monolithic and isolated from the exterior as much as is feasible.

The masonry mass should be insulated to the highest degree feasible.

The inner door height of the oven should be 60-65 percent of the dome/vault height.

If wanted, the chimney should be at the front of the oven, outside the inner door, and should be sized at 10-15% of the door size, more for short stacks, less for tall stacks.

These guidelines apply for round, barrel, or square ovens.
Thanks! You've obviously done this before. I'm planning on using the 4.5" of firebrick width all the way around including the dome and back wall.
With 1" of Heat Stop 50 cladding. Then 2" of FB Blanket and aluminim foil, followed by chicken wire and another 1" of cladding. Do you see any problems with this design? That would give me 8.5" of thickness.
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Old 06-19-2012, 10:03 AM
Tscarborough's Avatar
Il Pizzaiolo
 
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Default Re: "Flat back wall" vs. dome/rounded shape

I don't think the foil does anything, but other than that it looks good. Use the FB plans for the stand, they are much better.
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Old 06-19-2012, 11:16 AM
WJW WJW is offline
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Default Re: "Flat back wall" vs. dome/rounded shape

What Tom said!

DO NOT follow the Allan Scott design for the stand! In his design there is no insulation between the stand and oven. Bad.

As far as thermal mass/cladding...the amount you use is dictated by how you want to use the oven. In simple terms, the more mass....the longer your oven will stay hot. But (since there is no free lunch) the more mass you have, the longer it takes to get up to temp.

I have a barrel vault style, but with zero extra cladding/mass. Just bricks in a single layer. My floor is a single layer of firebricks (so 2.5 inches thick), my walls are sigle layer of fire brick layed stretcher (so 4.5 inches thick) . My vaulted roof is single layer of brick (4.5 inches thick). No added cladding but lots of insulation. Three inches of Insblock19 under the oven, four inches on each side, and three inches of Inswool on top with some scrap pieces of Insblock on there as well.

I've been cooking about two months in my oven. I have thermocouples placed in the masonry so I can graph on my laptop the temp curve. With my set up my oven goes from completely cold to what I consider completely heat saturated in about two and a half hours. By that I mean that the surface of the bricks inside the oven are around a thousand degrees or a bit more, and the portion of the brick farthest from the fire (between brick and insulation) are right around 650 degrees. That is too hot to cook in in my opinion, but I've ened up there a couple of times and had to let things cool to avoid burning the pizza crusts.

I can get to a point I consider good for bread in about a two hour hot burn followed by an hour and a half to cool down and equalize. With that two hour burn my interior will be eight or nine hundred but the outside edges of the masonry are still soaking heat away from the interior. During the next sixty minutes or so (with the door open) the interior of the oven drops to around 550 or so so after being wet-mopped, and the exterior portions of the masonry will continue to rise getting up to 600 or a bit more. I then close the door for thirty minutes and the interior of the oven is around 575 (good for bread.)

I could get to pizza cooking temps in an hour with a hot burn, but the oven wouldn't be saturated and I'd think the floor would start cooling if I was cooking a bunch of pizza.

Assuming I shut the oven down at pizza temps around nine pm (say around 800 interior with exterior edges of masonry around 680) , the oven interior will be around 590 the following day (twelve hours after the fire goes out)...the exterior margins of the bricks will be 625. (Good bread baking temps)

The following day (36 hours after the fire went out), the oven will be 375. (Calzone temps)

On day three (60 hours after the fire goes out) the oven will 250 degrees. (Pork shoulder, ribs, or short ribs. )

On day four (72 hours after the fire goes out) the temp will be around 160. Not good for much more than drying tomatos in my opinion.

I'm sure if I had more thermal mass/cladding I could cook another day but the oven stays plenty hot for my uses.

Everyone says that you need more mass for multiple batches of bread. I have not found this to be the case. I have been doing up to twenty loaves of sour dough on a bake day (done over the course of three batches) . I'm starting with the oven around 575. When I finish the third batch I'm still between 490 and 500. I'm sure I could do five batches of bread and still be above 425.

Have fun!

Bill
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