double chamber cob oven plans - download

These ovens make a great central focus for very fun pizza parties.
The clean burn is not just the second chamber, but the proportions Ernie and Kiko worked out for how tall the opening is between the two chambers, how big an air-hole goes in the fire door, and the insulation behind the dense baking ceiling. The right proportions help send the flames on a long, rolling path, burning more of the fuel before it exits, yet still preserves the baking qualities of a traditional dome oven. You can vary the dome height a bit, for more of a pizza oven (flatter) vs. a bread oven (rounder), as long as the proportions stay the same.

Below: One of our workshop hosts invited a 3rd-generation pizza baker from a local Italian restaurant. He told us about the wood-fired oven his grandfather built (using stones for extra thermal mass), and brought a big bucket of slightly-too-old pizza dough so we could practice tossing without worrying about dropping it on the ground. (We had other dough already made up fresh for our own consumption).
This particular party was part of Portland's Village Building Convergence, so the crowd was mostly young adults, with a few neighborhood kids. But there doesn't seem to be any limit on who will show up if you start baking pizza. We've done parties with the in-laws, school kids, or just about anybody. When Ernie was baking at Cob Cottage Co, he would make quadruple the dough compared to how many people were on site at the beginning of the day - for example if he was baking for a 15-person workshop, by the time the pizza was ready there would somehow be about 50 people on site ready to eat. Decorate-your-own-pizza preparation tables help a lot with that kind of crowd. But he'd have the oven piping hot, so it could turn out a thin-crust pizza every 4 minutes or so.

Thermal mass ovens are most efficient when heavily used: for longer baking sessions, and ideally every day, so yesterday's heat is still available for use.
If you are interested in shorter baking sessions or once-a-week or less, I believe the plans mention how you can reduce the thermal mass to 1" or 2", and increase the insulation thickness, for better fuel efficiency.

-Erica

There is definately some artistic stuff here. I love the frog and the snail. Good stuff

I was excited to buy this book as I have a rather intriguing possibility: reactive an old communal beehive oven in a medieval hill town in Italy!

The oven is part of my house, specifically it is in the cantina, located directly under my living room. The oven is big, around 8 feet deep and was used regularly until about 40 years ago. The firebrick in pretty good condition, chimney is stone and extends two stories up, past the roof line and has excellent draw (probably too much).

Challenges and changes I am contemplating:

1) The biggest issue is that the oven isn't directly connected to the chimney so just like the usual cob stove, smoke comes out the bread door and can fill the cantina and house. It does however have an area in front of the bread door that I could turn into a small first chamber and add a burn door. The chimney entrance is high up near the ceiling but right there so I imagine the smoke could be channeled fairly easily with the two chamber design.

2) When the oven is cooking, the whole house cooks - not so great summertime! I imagine I can just use the existing structure as my "brick layer" and simply add a good layer of insulation (perlite + clay).

Any comments, pointers, anyone who has attempted a similar project?

Thanks,
Romana

8' deep is really huge! It sounds like it could easily bake all the bread for an entire village. Do you see a chance of actually using the full size of this? If not, I think it would be inefficient to heat it all up to use half or a quarter of the floor. I might consider modifying it to make the baking chamber shorter and converting the front portion to the reburn chamber connected to the chimney.You could probably even do it without significantly altering the existing except for a hole for the chimney, mostly adding new lining.

Is the exterior of the oven exposed so that you could add perlite-clay to it? I expect that would make a lot of difference to comfort.

Another approach if you don't think you can properly use the whole existing size of the oven would be to do all the modification on the inside, adding a good layer of perlite-clay and a new brick liner shaped into two chambers. This would be a lot trickier and probably more expensive, but you could get a perfect interior profile for the reduced size and keep the existing exterior appearance. I might approach that by building up the new brick liner a few courses at a time and stuffing the cavity between that and the original with perlite-clay.

Glenn Herbert wrote:8' deep is really huge! It sounds like it could easily bake all the bread for an entire village. Do you see a chance of actually using the full size of this? If not, I think it would be inefficient to heat it all up to use half or a quarter of the floor. I might consider modifying it to make the baking chamber shorter and converting the front portion to the reburn chamber connected to the chimney.You could probably even do it without significantly altering the existing except for a hole for the chimney, mostly adding new lining.

Is the exterior of the oven exposed so that you could add perlite-clay to it? I expect that would make a lot of difference to comfort.

The plan is for the oven to serve the whole town and beyond! Lots of bread, cookies, but also pizza. To give you an idea, the baker interested currently has a commercial enterprize that does 2000 of the big 5 pound loaves of bread a day. I imagine if she fired it up she would use the oven for several hundred of them plus pizza and other baking. Some years ago it was used to make something like 800 pizzas for a special (one day) event!

The oven is part of the stone walls of the house on two sides but the top can be accessed from one side. I agree a nice layer of insulation would make a lot of difference both in comfort and the amount of wood necessary. My main concern is smoke pollution.

Well, if you have a plan to fully use the beast, great! Then I think your idea is probably the best way to handle it. Pile on the insulation wherever you can reach on the dome.

Ernie or Erica would be the best ones to comment on technical aspects of scaling their oven design up to get the reburn and minimize smoke.

This looks pretty cool but, why don't you put a feed tube in the back to the burn chamber?
This could double as the air intake and could self feed?

I'm thinking of a pizza party where you want to 800 deg. to be there for several hours..

I definitely want to build one of these, but all of the links for the plans stopped working 4/1/17.  Is there another place to find these plans?

Thanks for asking.
I just attached the plans to this thread, using a new feature of Permies that allows paid content.  So there should be purchase links above, instead of broken links.
(Please let me know how it works for you!)

scott romack wrote:This looks pretty cool but, why don't you put a feed tube in the back to the burn chamber?
This could double as the air intake and could self feed?

I'm thinking of a pizza party where you want to 800 deg. to be there for several hours..

We already get several hours at pizza-baking temperatures with this design.  Personally, I think bringing in additional fire/air while baking could get unnecessarily complicated.
Good insulation, over a good thick inner layer of thermal mass (the plans allow for anything from 2" to 4" of dense earthen masonry) will hold very hot temperatures.  Our rule of thumb is about an inch per hour, so you'd build a thicker inner layer for bigger, longer baking sessions; you'd build a thinner, lighter oven if it's just for the family and you want faster heat-up and cool-down.

These ovens are routinely used to provide 4-minute pizzas for parties of 30+ people, usually we have guests 'decorate' the pizzas because the cook is fully occupied just getting them in and out of the oven that fast.
You run the fire quite hot, and therefore relatively clean, for a few hours before baking, then you use a second, insulated door to trap heat and bake continuously for as long as you have dough/ the oven holds heat.  
Most people (including parties with multiple families) run out of dough before the oven runs out of heat.

For all-day special events, like pizza for multiple class groups on a big field day, I've seen bakers keep a stash of coals on one side of the oven while baking, and rake them across to the other side from time to time.  
It is not perfectly even, they may also need to rotate smaller pizzas around the floor a couple times while baking to avoid uneven heating, but it does allow you to keep cooking and "re-heating" the oven simultaneously for a very long time.
This lower-temperature fire (800 is pretty cool for a fire) does get smoky, so this trick is best used with foods that taste good with a little bit of hardwood smoke.  Pizza tastes awesome with a hint of smoke.

The idea you suggest, with a rocket feeding fire into the oven, has been done before.  
I have seen rocket ovens that feed more fire in the back, or from one side to another, either under the floor or directly into the oven chamber.  However there are some technical considerations with suspending the floor over the rocket stove, without creating uneven hot spots in some parts of the floor and cooler areas in others.  

If you are looking for an oven that heats up faster, and can/must be fed continuously while baking, you might try:
Tim Barker's rocket barrel oven, https://permies.com/t/60370/Rocket-Powered-Oven-build-super
or the Green Rocket production ovens. http://www.woodfiredpizza.org/rocket-oven-construction.html

Hi guys, a couple of questions as we are going to build this oven soon, according tothe plans.

1 Considering the re-burn going into the exhaust pipe, does the pipe need to be stainless steel or will a copper pipe stand the heat?

2 I would like to tune the oven to heat up faster and cool down faster so it suits our small family needs better. To bake about two pizzas and one bread Will take about an hour and a half of baking time or a little less. Do you think an inch of thermal mass should be about right for that or will I risk it's cooling down too fast? I have obtained Chamotte Stones an inch thick for the base to go with it. Also what would you recommend as maximum installation thickness for such a setup?

3 in the book you mention that the exterior may not be treated in a way that the oven cannot breathe. How does simply linseed oiling it fair in that respect? Does that also inhibit breathability? And does polishing the exterior clay make a difference?

Thanks a lot!

brian haitz wrote:Hi guys, a couple of questions as we are going to build this oven soon, according tothe plans.

1 Considering the re-burn going into the exhaust pipe, does the pipe need to be stainless steel or will a copper pipe stand the heat?

2 I would like to tune the oven to heat up faster and cool down faster so it suits our small family needs better. To bake about two pizzas and one bread Will take about an hour and a half of baking time or a little less. Do you think an inch of thermal mass should be about right for that or will I risk it's cooling down too fast? I have obtained Chamotte Stones an inch thick for the base to go with it. Also what would you recommend as maximum installation thickness for such a setup?

3 in the book you mention that the exterior may not be treated in a way that the oven cannot breathe. How does simply linseed oiling it fair in that respect? Does that also inhibit breathability? And does polishing the exterior clay make a difference?

Thanks a lot!

Hi Brian,
1 - I would use chimney pipe rather than copper.  Could be stainless, or black-painted steel stovepipe.  
This is mostly because I don't know how the copper would perform (whether it might melt for example).  Copper is such a good conductor, anything touching it would get very hot!

2- I think you would be ok with 1 inch of thermal liner, plus lots of insulation.  If needed, you can add more wood, or push the coals to one side to continue heating while baking the first pizza(s).
I would use at least 4" insulation, 6" might be better for your purposes.  (10 cm / 15 cm).  You may use more insulation if you can get it to hold onto the oven, a perlite-clay-fiber mix might do well.  
I don't know of any maximum, maybe leave a gap of at least 40 cm (15-18") below the roof?

3 - One coating of linseed oil could be OK.  Polishing the clay could be OK.  But I have seen ovens crack a lot, and polishing does not seem to help (sometimes makes it worse).
If you are trying for 'waterproof,' what you really need is a roof to remove the water so it does not contact the warm oven in the first place.

Hope that helps!

If you lived closer, you could come build one with us in person this month: we have an oven workshop in Idaho June 30-July 2.  http://naturalhealthtechniques.com/workshop-double-chamber-cob-oven/

Hello Erica,

Thank you loads for your reply, it's great to get the assertion from you guys directly! Highly appreciated and I would love to join one of your workshops if it wasn't for the distance < maybe there will be one in Europe one day.

So we went ahead and built the oven with 1 inch of thermal Mass and unfortunately as it was my first time building something like this I made all the mistakes you can imagine. The most crucial one being that I didn't get the mixture right for the thermal mass, It was too wet and therefore kept slumping and the whole thing just didn't go very well. I decided to mark it down as experience and make another oven and given the second opportunity I decided I will try to build a slightly lower oven to favour Pizzas. This time the mixture felt really good and the build went very well. The ratio of sand to clay was about 4/1 and as it dried out there were no cracks and the thermal mass dome looked Great so I was quite confident. As my daughter's birthday came up I thought I can use the oven the way is and add the rest of the installation later. Sadly now after three firings the thermal lining has developed a lot of fine cracks and even one larger one which is about a 10th of an inch. Is it possible that I fired the oven too hot? I am a bit surprised since all the tests of the mix went well and there were no cracks whatsoever after completely drying the thermal lining. The insulation had not dried out completely before firing so could that have caused the cracking? the inner lining however worked great in terms of efficiency. We got the oven to 350 Celsius in under an hour , baked 4 great pizzas and even with the thin installation we have at the moment we had no problem baking one round of breads afterwards. After that the oven still measured 130° Celsius

Would there be at any point in trying to remove the installation layer and patch the thermal lining from both sides or is this oven going to have to come down?

Obviously very disappointed but thanks again for all your help and advice!

Hey, I got the email about the bundle, and somehow I've been all out of money lately. As a strategy I wonder if it is possible to sign up for the $75-bundle and get the downloads and pay later? Hm? No? You see, somehow it tends to work like knowing you owe someone, then you find the money. Silly question?

I used one of these ovens in Catalonia, Spain a few years back and it was great. Been planning to build one in my garden for a while now and would like to get hold of the plans. How can I purchase them? Everyone I have asked sends me to this page which then directs me to the 'mega bundle' with dvd's etc.. and also says I can purchase individual plans but I don't see a link to get the plans for the double chamber oven. Can anyone help or point me in the right direction? Thanks - Mike

Brian - The cracking could be from one (or both) of two causes: 1) Baking with uneven insulation can cause parts of the interior to expand more rapidly than other parts, or to expand inside while shrinking/staying smaller on the outside.  A lot of stress to put on the materials.

2) Even with 4 sand:1 clay, you could be working with too much clay, depending on your local materials.  
I might suggest testing batches up to 10sand:1clay, and/or adding some fiber.  Ceramic wool fiber, or even a natural fiber such as chopped straw or animal hair, can help the mixture resist cracking, dry more evenly, and respond more evenly to the initial firings.  Occasionally we find that our local "sand" already contains sufficient clay, and any additional clay will just cause cracking to be more intense.


Nancy - I hear everyone suggesting that you should 'scandalize' the oven (reduce its total size), and/or poke more holes in it.  I would resist these well-meaning suggestions.
You can conserve the original oven's shape and function, while adding a "smoke shroud" over the top.  One New Zealander did a project like this by wadding up some plastic bags over the door where the smoke goes, making a generous open-mouthed funnel or chimney throat leading back to a chimney connector.  He used the wadded plastic bags as formwork to build a throat out of clay.  In his case he was able to support the new smoke-scoop entirely over the existing oven, instead of building a second chamber in front.  
 
If it sounds easier, you could also try a basic overhead metal shroud, with or without a vent fan.  Like an oven vent hood over a propane kitchen stove.  Just be sure to support it on a roof framework instead of bolting into the oven's masonry.  Old masonry does not love having holes drilled in it, especially masonry that cycles hot and cold.

Yours,
Erica W

I'm debating buying these plans. But I need to know if they can be scaled up to a 6ft diameter, and what kind of brick is used for the floor? Ordinary ceramic housebrick is easy to come by and cheap in my locale but refractory brick can be pretty expensive.

The plans just call for 50 bricks for the size of oven described. You'll need more if you scale the oven up. Since you're building a fire inside you'll need fire bricks. Otherwise they'll crack, and crumble.

Is there a way to buy the plans if I'm in Canada?

Samuel Plante wrote:Is there a way to buy the plans if I'm in Canada?

Not that I'm aware of.

Do the plans cover questions like these?
what materials can replace cob if you don't have access to clay or if i can purchase some sort of commercial product.
is it weather proof/how to weather proof
do plans show how to scale size up or down based on my available space/desired uses
and any other questions that i should ask but haven't got a clue

on another note. in another thread i asked about permies in the north okanagan and someone mentioned your name but i see you are in washington and i'm in bc between armstrong and salmon arm. do you know of anyone in this area i could reach out to for conversation/permaculture input as i am quite new to the journey.
thanks for any input
cheers   james

hiya, hoping to build this sometime this spring/summer. James did you end up building one? Would love to connect or build together! or just for a pizza party eventually (ps also new to the website so maybe not great at using it)

I just noticed the link in the original listing above to the "mega package of plans and stuff" was not working.  It is now! Do take a look either above, or here:

https://permies.com/t/40993/Ernie-Erica-Wisner-Rocket-Mass

And there is also some more info about the plans in general on that thread, which may be useful

hiya, hoping to build this sometime this spring/summer. James did you end up building one? Would love to connect or build together! or just for a pizza party eventually  (ps also new to the website so maybe not great at using it)

hi pia
nope, haven't done it yet. still working out the details and collecting materials. not sure what i will build first, but most likely all projects(pizza oven, double chamber oven or any of the many rocket style projects) are slated for next year. too many other stuffs to do this year. if you do get it done, keep us posted with pics n stuff.

chelan is a mere 5 hour drive to where i live so we will have to do some serious planning for that pizza party  that said, since i won't be building til next year it does give lots of time for planning. if you get it done this year you can come help build, (adding all your practical expertise) then we can have that pizza party. my wife and i would definitely have a space for you to stay over. bit of a drive home, especially if you had a beverage or 2 with that pizza. lol

I just noticed the link in the original listing above to the "mega package of plans and stuff" was not working.  It is now! Do take a look either above, or here:

thanks, jules, wondered why why i hadn't heard back.

cheers    james

you sure you're not in Canada?? 5hrs from Chelan huh? that sounds far! We're seeing what we can source to start with. found a fairly local potter who might have some clay for us, got our bale of straw. start trying different cob mixtures sometime, hopefully the kids get into it and help us experiment! we'll put up some pics as we go, sure!

you sure you're not in Canada??

yep, i am pretty sure i am in canada, in the north okanagan, near a small town called enderby in bc.

pia, if you click on the persons name in the left column you can often read that person's profile which may include their location.

the children should have fun playing in the mud, i can't wait to do it myself.

looking forward to pics and updates

It looks like Ernie used single wall stove pipe for the exit out the door. That pipe must get really hot if its single wall. Wondering what your experience is with that single wall, double wall or triple wall directly out the doorway smoke exit.  I got his plans for the two chamber Earthen oven the biggest chimney pipe opening he recommends is 6 inches.  If I were to use a triple walled stove pipe to exit the top of the cob doorway would that be over kill?  Since triple walled pipe is 8 to 10 inches wide from the outside I wonder if thats too big for the archway to support? Basically I am deciding between buying 4 inch insulated pipe, 5 inch insulated pipe, or 6 inch insulated pipe and wanted to hear all your thoughts prior to make that purchase

Matteo, welcome to the forum.

Maybe one of our stove gurus, like Thomas or Peter will see your questions and will be able to give you an answer.