My WFO design

[adios pantalones]

My experience with these firebox arrangements is that the fire will be sucked into the oven pretty easily. In a kiln, this starts at around 500F, and the chamber is a ball of fire when the air temps are 1200F- which is easy to achieve.If I want more top heat, close the door and let the fire rip. If I'm wrong, I'll throw some wood in the back before I cook- I aint too proud to admit a mistake Plus- I'd still have a smoker box built on there.

[Jet_deck]

....If I want more top heat, close the door and let the fire rip....

At that point, where do the coals get their air?

[scott123]

I'm not making any promises, but if I were building a kiln/pizza oven hybrid, this is probably what I'd try first:

[scott123]

You use the lower flue for pre-heating the oven, but during the bake, when you want the smoke away from the pizza, you use the upper flue.

[adios pantalones]

At that point, where do the coals get their air?

The firebox has primary and secondary air inlets- air must pass through the fuel bed to get into the cooking chamber, creating an efficient burn (like a bellows under a coal pile). During heat up, air never enters the oven door (ideally).

[adios pantalones]

You use the lower flue for pre-heating the oven, but during the bake, when you want the smoke away from the pizza, you use the upper flue.

Not a bad idea- you just need a damper for each flue. I will probably just go with a noborigama (climbing kiln) style firebox- the first dome in this pic
edit: during trial runs, if the floor gets too hot, I'll slow down the fire, which lets it rise across the dome.

[pizzaneer]

That picture's impressive. I take it the firebox is on the left, and the heat/combustive gasses are ducted through the two ovens? 

If you are going to craft a pizza/bread oven built on this concept, you should name it, maybe even think about patenting it. I don't say that lightly- I know how tough it is to patent something.  I think your concept is very interesting, and I really want to see it come to realization.  It's an ancient oven-building technique, which in these days of mass-production doesn't get the replication it deserves.

[adios pantalones]

Pizzaneer- yes- the lower dome is the firebox for the kiln. There's a mess of crossdraft designs- some noborigamas have several chambers and take a couple weeks to fire, people working around the clock. Not sure if it rises to patentability- I know more than one person that heats a pizza oven with residual kiln heat. My kiln has a "Bourry box" design. The advantage of that is that a large charge of wood can be put in at once, and the air always goes through the fuel until it's burned to coals.

Check out this monster kiln

[adios pantalones]

Heres a wfo that a guy built next to his 4 chamber kiln in Seagrove, NC (pottery capital of the US)- I assume he built this for fun while he was firing the big kiln next to it (I took a mess of kiln pics there- but only one pizza oven pic). I think they just shovel coals out of the kiln into this to heat it- the kiln coals get feet deep.

notice the baby kiln built on the left of it. He has his kids out there making pots etc in the studio- I'd bet that was their first kiln build

[scott123]

AP, one thing to keep in mind- if you have any hope of getting proper pizza making temps, you should be shielding the floor from any direct heat from the firebox.  The goal should be a freakishly hot ceiling that then heats the floor via IR.  Firebox heats ceiling, ceiling heats floor.

[adios pantalones]

AP, one thing to keep in mind- if you have any hope of getting proper pizza making temps, you should be shielding the floor from any direct heat from the firebox.  The goal should be a freakishly hot ceiling that then heats the floor via IR.  Firebox heats ceiling, ceiling heats floor.

Thanks! Thinking about it like that helps. The firebox will be lower, and the flues relatively small, which *I think* should created enough of a barrier.

[Jet_deck]

Check out this monster kiln

Is all that wood being stored or do they light it right where it is at?

[adios pantalones]

That's all being stored- I was curious why they did that- maybe it's how they measure what they'll need. A fire is started in the lowest chamber- when the first ware chamber is hot, they start adding wood through a hole ("side stoking") the next dome is fired, when that's hot, they stoke the next, and so on- that's why it takes so long

[Jet_deck]

I am trying to think what would need to be different in your design than any white oven or your basic (old) Coal fired white oven.  Other than Anthrecite (sp) burns hotter than wood.
Look at reply #8 here: http://www.fornobravo.com/forum/f2/white-oven-vs-black-oven-2685.html

[shuboyje]

This design isn't really a white oven, and the best I have seen neither are most of the big old coal ovens.  With a firebox bellow the oven that directly heats the oven chamber this is closest in design to a french Guillard bread oven.  Getting this design to pizza temperatures with the proper balance of top and bottom heat is gonna be tough.  I personally think your two best options would be:

1.  Fully insulate between the floor and and firebox bellow and then build an adjustable throat where the flame enters the oven chamber.  This throat can be used to direct the flame down to the floor during heat-up and then change the angle to provide top heat during cooking once the floor is charged.

2.  Build a removable layer of insulation that sits between the firebox and the cooking floor.  It would be removed during heat up to heat the floor, once the floor is charged it would be put in place to stop the floor from super heating while bringing the dome up to cooking temperature and during cooking.

[adios pantalones]

This design isn't really a white oven, and the best I have seen neither are most of the big old coal ovens.  With a firebox bellow the oven that directly heats the oven chamber this is closest in design to a french Guillard bread oven.  Getting this design to pizza temperatures with the proper balance of top and bottom heat is gonna be tough.  I personally think your two best options would be:

1.  Fully insulate between the floor and and firebox bellow and then build an adjustable throat where the flame enters the oven chamber.  This throat can be used to direct the flame down to the floor during heat-up and then change the angle to provide top heat during cooking once the floor is charged.

2.  Build a removable layer of insulation that sits between the firebox and the cooking floor.  It would be removed during heat up to heat the floor, once the floor is charged it would be put in place to stop the floor from super heating while bringing the dome up to cooking temperature and during cooking.

All reasons I went to the offset firebox design (crossdraft) rather than the under floor.

[shuboyje]

All reasons I went to the offset firebox design (crossdraft) rather than the under floor.

I haven't been around much this week, I saw that proposed, guess in my skimming I didn't notice you had changed your plans.

At this point it becomes very similar to an old style coal oven.  Where do you plan to locate the flu openings?  Will you have a secondary flue opening above the door to catch the smoke when it is open?  I think you are on the path to a functional oven now, but I do think it is a design more suited to East Coast US style pizza cooked in 3 or 4 minutes.  Is that what you are after?

[pizzaneer]

If it's good enough to make pottery, with all the complicated glazes (thats COMPLICATED), simple bottom - top heat calculations at a relatively low temp should be easy.  I like the crossdraft, U-shape supply with adjustable vent.  It's close in concept to the LBE.  Can you take some pictures of the other potter's ovens?  Are they much different?

I'm really looking forward to seeing how it turns out, with you and Meesh collaborating.  I live in an area with lots of good clay, plentiful firewood, and my wife used to make pottery in a little kiln - I'm thinking of giving this a try too.

[adios pantalones]

I haven't been around much this week, I saw that proposed, guess in my skimming I didn't notice you had changed your plans.

At this point it becomes very similar to an old style coal oven.  Where do you plan to locate the flu openings?  Will you have a secondary flue opening above the door to catch the smoke when it is open?  I think you are on the path to a functional oven now, but I do think it is a design more suited to East Coast US style pizza cooked in 3 or 4 minutes.  Is that what you are after?

Plan is to have the oven hot enough that I can have good coals/no smoke when it's time to cook. I would hope for a 90 second pizza, and if it's 3 minutes I won't be disappointed- while I love pizza as much as the next guy, I don't have the experience to appreciate/demand a specific style.

The "throat", from the firebox, will be low so that heat rises and rides up the dome. The flue to the chimney will be low on the other side of the dome- this increases the interaction between the heat and the dome by maximizing the residence time. This design requires a higher chimney to get to kiln temps- Olsen says 3' for each 1' dome height, plus 1' for each 3' lateral travel from firebox to chimney. I don't need to get to 2400F, but chimney brick is cheap (can use commons), and I can damper down as much as I like- so I might have a 5' chimney.

[adios pantalones]

I want to say again that I really appreciate the suggestions, collective wisdom, and the discussion here. My design has changed quite a bit because of everyone's input.