Author Topic: My WFO design (Read 3560 times)

adios pantalones · « **on:** June 21, 2012, 01:39:27 PM »

Basing this on the "Phoenix fast fire" wood fired pottery kiln design. This is a half-barrel style dome. A door could be put on each side if desired, allowing you to rock a couple pies at once.

The firebox is under the floor, heat and gases enter the cooking chamber through a slot on the other end. Sort of a "gray oven".
The exhaust gases exit through the chimney flue on the opposite end from where they entered.
The door would be covered- either bricked (during warmup) or with a kaowool backed plate. The firebox and chimney design eliminates any door height considerations.

This heats the floor first, but pushing coals to the back would reduce this if necessary. Heat use should be very efficient, though it requires more chimney for draft.
Insulation will be full IFB's (I have hundreds of used light firebricks kicking around)

The under-floor firebox could also be used as a smoker box as well, and more heat can be added at any time without opening the cooking chamber. I could get this design glowing almost white (2300F) with enough chimney- which I may do just on principle

My questions- is dense castable refractory OK for a floor?
Are you normally shooting for a hotter dome than floor?

scott123 · « **Reply #1 on:** June 21, 2012, 02:08:31 PM »

With the bottom heat source, I think you're basically entering the LBE zone- which can get a little frustrating. With your ceramics experience, I think you should be able to troubleshoot it easier than most, though.

In bottom heat scenarios, it's all about redirection. You're not just shooting for a hotter dome than hearth, but a LOT hotter dome than hearth- 850ish hearth, 1000+ dome- and these numbers only apply if the dome is low enough. In bottom heat settings, this usually takes some major alchemy.

Pushing the coals to the back to reduce floor heating isn't going to be enough. You're going to need to deflect the heat away and over the floor. Those light firebricks you have plenty of- I'd put those both underneath the floor and up the edge as well to form a bit of a lip, so the heat has to go up and around the hearth.

The other thing that caught my eye is the smoke. It's hard to tell, but it looks like the pizza will be at smoke level. A tiny amount of smoke flavor from briefly doming the pizza at the end of the bake is pleasant, but you definitely don't want to bake the pizza submerged in smoke for the entire bake.

Any idea of how tall the dome will be? Ideally, for wood fired pizza, you want to shoot for less than 12 inches. That kind of vertical profile could be difficult for firing pottery.

I don't believe castable refractory is food safe. Firebrick is preferable for the hearth.

adios pantalones · « **Reply #2 on:** June 21, 2012, 02:17:15 PM »

Quote from: scott123 on June 21, 2012, 02:08:31 PM

With the bottom heat source, I think you're basically entering the LBE zone- which can get a little frustrating. With your ceramics experience, I think you should be able to troubleshoot it easier than most, though.

In bottom heat scenarios, it's all about redirection. You're not just shooting for a hotter dome than hearth, but a LOT hotter dome than hearth- 850ish hearth, 1000+ dome- and these numbers only apply if the dome is low enough. In bottom heat settings, this usually takes some major alchemy.

Pushing the coals to the back to reduce floor heating isn't going to be enough. You're going to need to deflect the heat away and over the floor. Those light firebricks you have plenty of- I'd put those both underneath the floor and up the edge as well to form a bit of a lip.

The other thing that caught my eye is the smoke. It's hard to tell, but it looks like the pizza will be at smoke level. A tiny amount smoke flavor from briefly doming the pizza at the end of the bake is pleasant, but you definitely don't want to bake the pizza submerged in smoke.

Any idea of how tall the dome will be? Ideally, for wood fired pizza, you want to shoot for less than 12 inches. That kind of vertical profile could be difficult for firing pottery.

I don't believe castable refractory is food safe. Firebrick is preferable for the hearth.

Thanks for the reply!
This is still in design- I'm not married to the under-floor firebox, and it sounds like something I should consider abandoning. I could just offset the firebox to the side and go with a cross-draft design to get around the floor heating issue (this is why I came here- good stuff!).

I would anticipate heating the bejezus out of it and not cooking until I'm at coal stage to avoid smoke issues, but a "bag wall" could be used to direct the heat/gases up. This is a simple low wall. Generally the heat would rise and sort of "tumble" as it approached the dome peak.

Is that dome height meant to make the radiant heat work better for you? My first drawing had the dome at about 15"- in the ballpark for this, but that is negotiable as well.

Tory · « **Reply #3 on:** June 21, 2012, 02:46:43 PM »

I'm considering making my own WFO to bake pizza and artisan breads. So I'm sort of wondering if there's one particular type of wood that is ideal for use in WFO's. Perhaps wood that will NOT impart any of its own flavor (such as hickory or mesquite might do) ??

TXCraig1 · « **Reply #4 on:** June 21, 2012, 02:47:22 PM »

adios,

What type of pizza do you plan to bake?

TXCraig1 · « **Reply #5 on:** June 21, 2012, 02:50:19 PM »

Quote from: Tory on June 21, 2012, 02:46:43 PM

I'm considering making my own WFO to bake pizza and artisan breads. So I'm sort of wondering if there's one particular type of wood that is ideal for use in WFO's. Perhaps wood that will NOT impart any of its own flavor (such as hickory or mesquite might do) ??

Any dry hardwood will work fine. I usually use oak for its fuel density and low cost. At WFO times and temps, the wood will not impart any flavor in your pizza and there is no need to consider flavor from the wood into your decision.

CL

adios pantalones · « **Reply #6 on:** June 21, 2012, 02:59:54 PM »

Craig- I tend toward thinnish crusts, though I cannot navigate the terminology that I see used here. I'd hope to bake other stuff as it cools and, as I mentioned- use the oven as a small smoker

edit: I gave a friend a few hundred pounds of clay- he made a simple dome oven that he loves. I'm enjoying the design aspect of this as much as anything- therefore the un-necessary complexity

TXCraig1 · « **Reply #7 on:** June 21, 2012, 03:19:26 PM »

My concern is that to have any meaningful radiant heat on the pie, you may have to preheat the oven for a long time (a day or more maybe?). Without enough mass and insulation in the dome, it might not even be possible to get it hot enough to bake a Neapolitan-style (thin) pie. On short bakes (sub-3 min), I think you might have difficulty getting color on the top due to a lack of radiant heat, and you may burn the bottom.

adios pantalones · « **Reply #8 on:** June 21, 2012, 03:30:36 PM »

Craig- I see what you are saying- I am probably going to a crossdraft design to avoid the bottom heat issue. Whatever design I pick- it will be 4.5" hard brick in the dome with 4.5" insulating firebrick for insulation. If the dome needs to be lower to help radiant heat, I can do that.

I estimate that I could get it to over 1500F in maybe 6 hours. Heck- I have got my kiln to 2380 F in 16 hours before- with a full load of pots.

Here's the 15' chimney on that sucker

TXCraig1 · « **Reply #9 on:** June 21, 2012, 03:49:38 PM »

With a fire in the middle of my 47" wfo, the bricks in the wall don't hit 900 for 8 hours or so - if that quickly. If it's below 70F outside, it might be 10-12 hours or more.

I have little doubt that you could bake a great NY style pie in that design, but I don't think it will work as well for Neopolitan regardless of the dome height. I could be wrong, but that's my gut feeling based on my experinces with different levels of radiant heat from the fire and the walls.

CL

adios pantalones · « **Reply #10 on:** June 21, 2012, 03:58:11 PM »

With an offset firebox design and a good chimney, the wood will gasify and much of the burning will happen efficiently in the cooking chamber as the gasified wood and air mix. Outside temperature has about zero effect on getting good internal temp with this design.

Having the fire in a separate chamber actually increases the efficiency a great deal if controlled properly.

Add to that- reducing the air into the firebox actually increases temp- as excess air cools the fire considerably.

I've seen it work for miniature kilns, which need to get to cone 11+ (2370 F- ish), in addition to my full sized kiln.

TXCraig1 · « **Reply #11 on:** June 21, 2012, 04:34:07 PM »

With respect to Neapolitan pizza anyway, keep in mind that air temp in the oven is not the same as oven wall temp (which will almost certainly be a great deal lower) and the latter is more important (as is radiant heat from the fire).

Ambient/external temperature will make a difference - not in the time to reach a set internal temp per-se, but in the time it takes to heat up the mass of the oven. The increase in time can be surprising.

Don't get me wrong. I hope your oven works great, and I'm excited to watch your progress. I'm just trying to give you some things to think about when designing the oven.

Craig

Tory · « **Reply #12 on:** June 21, 2012, 04:58:37 PM »

I'm also sort of wondering if using fire bricks are necessary, or can you just use regular 'red' concrete bricks to make the oven?

I hear a lot of people talk about using fire bricks, but what I see on youtube videos seems more like they're using regular red bricks.

Tscarborough · « **Reply #13 on:** June 21, 2012, 04:58:45 PM »

What you are designing is a white oven. There are two options depending upon when you plan on using the oven: While firing or after firing. What is your plan?

adios pantalones · « **Reply #14 on:** June 21, 2012, 05:33:27 PM »

Craig- understood!. I understand the wall temp vs air temp dilemma- but the quicker you put heat in, the quicker the mass will heat as well. Hey- I can cook the hell out of pottery, but this is my first foray into pizza ovens, so I do appreciate the insight (I said that if my kiln didn't get to temp, it'd be the biggest pizza oven in town).

Tscarborough- I thought that a white oven had no interaction with the combustion gas (a chamber is heated through the brick) and a black oven had a fire in the chamber?

Anyway- I'd like to heat without a fire going, but if I need more top heat, I'd deflect the flame upwards and have a fire going to give it some kick.

scott123 · « **Reply #15 on:** June 21, 2012, 07:17:29 PM »

Adios, another aspect to consider regarding pizza in a WFO is flame. Neapolitan pizza gets an 850 degree floor, 1000+ ceiling AND a tall flame/red hot embers in close proximity. If you have the firebox below, I was picturing the flame shooting up the side to the ceiling, but, with a firebox to the side, that may not still be the case.

I think there's going to be a magical dome heat, that, if you hit it, you don't need a close proximity flame, but it's going to be higher than 1000 AND it can't drive up the floor temp too dramatically. Can you do a 1300 ceiling with an 850 floor?

shuboyje · « **Reply #16 on:** June 21, 2012, 08:03:34 PM »

Rather then jumping into the design conversation I'm just gonna jump to pure logic. Why? I've dabbled with a potable design based off of the concept of operation for a fast fire kiln but in a stationary oven where size is less of an issue I don't see the benefit of a separate fire box no matter where you locate it. If you were building a commercial bread oven I would be right here advising you to build a guillard style oven, but for a multi function home oven the standard masonry black oven is the way to go. Tried and true.

adios pantalones · « **Reply #17 on:** June 21, 2012, 08:29:26 PM »

Quote from: shuboyje on June 21, 2012, 08:03:34 PM

Rather then jumping into the design conversation I'm just gonna jump to pure logic. Why? I've dabbled with a potable design based off of the concept of operation for a fast fire kiln but in a stationary oven where size is less of an issue I don't see the benefit of a separate fire box no matter where you locate it. If you were building a commercial bread oven I would be right here advising you to build a guillard style oven, but for a multi function home oven the standard masonry black oven is the way to go. Tried and true.

I like designing/building kilns and thought this design would be fun!
It's as much about the process as the product, maybe more.

Tscarborough · « **Reply #18 on:** June 21, 2012, 08:33:11 PM »

Your fire is not in the cooking chamber, hence white oven. You will need to use a small masonry mass in the burn chamber, large mass in the cooking chamber, all well insulated, of course.

shuboyje · « **Reply #19 on:** June 21, 2012, 09:34:36 PM »

Quote from: adios pantalones on June 21, 2012, 08:29:26 PM

I like designing/building kilns and thought this design would be fun!
It's as much about the process as the product, maybe more.

There is a ton of design to go into a well built black oven and in the end you will have a great and versatile cooking appliance.