Double Chamber Cob Oven

Hey Ernie, love your oven, this one.



Would love to see some plans so i can make one too.
Even just a rough sketch with the theory of what you're doing should be enough for me to figure it out i would think.

Thanks!

I am also interested in this.

The bake chamber is the same as normal. The secondary burn chamber has the main difference from a normal chimney in that it would be well insulated, at least at the bottom. It doesn't look so in the top. The burn door is important in that it restricts the intake air. note that it closes to the outside opening so it feeds air to both the bake chamber and the reburn chamber. But the baking door just closes the bake chamber off. The video seems to give all the information needed. I wonder how close a normal brick oven with a 3 wall flue comes to this.

It's a neat little oven; Works really well to.
What do you want to know about the oven?
We can discuss it here if you have questions.
We have the plans of the double chamber for sale just drop us an email.

When you say "cross sectional area" you mean the area of the pipe opening, right? As in the area of a circle A = pi*r^2

Any particular reason you chose a steel outer door rather than something that would provide some insulation? Do you think it'll make a difference?

Given that the air volume changes after combustion by a bunch, do you think restricting the air intake further and using a smaller fire would help retain a little more heat for your wood?

I guess what I'm saying is that it looks like your design allows combustibles to burn in the flue rather than in the chamber. Is the flue able to absorb much of that energy? It seems like restricting the air flow and having a smaller fire would mean less air volume in, but in order to prevent smoke you'd need less combustible material. I think that wasteful smoke is caused by two things fundamentally. #1 the fire isn't hot enough to burn those bits or effectively deal with them, things like excess moisture. This also means if you have way too much cool air (intake) coming in you'll cool the outer surface of the combustibles and this will cause smoke. This smoke is white and billowy. #2 combustible material is charring and not burning because of lack of oxygen, the remaining combustible gas goes up the flue in other words too much fuel or not enough oxygen. Which are essentially the same thing. This smoke is less "puffy" more "sooty".

If you think that's a worthwhile thought would you mind experimenting? I plan on building a stove soon so if you don't get the chance I'll give it a shot, but I'd appreciate your experience all the same.


Thanks for the great idea!

I made a mud oven a few years back. I couldn't shelter it due to occasional flames like in that photo above. It lasted a year or two but I wonder if Vermont has too much snow and rain for a mud oven? Oh yeah, and the goats liked to dance on it and eventually demolished it. I'm anti goat.

I'd like to build a brick oven on it's foundation.

Ernie Wisner wrote:It's a neat little oven; Works really well to.
What do you want to know about the oven?
We can discuss it here if you have questions.
We have the plans of the double chamber for sale just drop us an email.

Since I moved from Ohio to So Florida, heating is no longer a goal, but I'm looking for ways to self generate Air Conditioning, and get free from the grid. AC is a must here in the summer.
One approach I'm looking at involves using ammonia gas heat fired AC systems. But they would require a heat storage tank.
I'm wondering how hard would it be to harness the heat from a Rocket Stove into, say a tank of water, or salts, to store 210-250 degree liquid salts. I think any mechanics that would serve to heat a tank of super hot water would also work for salts.

There is too much wasted energy in the design from the video posted. The use of the "rocket" effect is utilized in a manor to minimize carbon monoxide and smoke which would be better (not recommended) for indoor use, but not much use other than this. If you are soon going to build that cob oven, I would create it in a manor that allows the exhaust rocket flame to vent inside the thermal chamber, otherwise the rocket effect would be more of a novelty.



These ovens are thermal batteries in that they can store a large amount of heat and dissipate slowly. DO NOT USE CONCRETE! Cob is a good material in that is cheap, holds adequate thermal energy and not prone to structural cracking from heat, but it will need to be protected from erosion caused by rain. There are other materials you will find for a more permanent structure if you do some research of wood fired pizza ovens but they are more costly. You want to maximize your efficiency by utilizing as much potential heat as possible from the fuel source so do not copy the design from the video unless the novelty flame is what you desire. Because each of these ovens are hand crafted, baking feels more like an art. You can with experience triangulate the fuel mass with environmental temperatures to reach target baking temperatures so you can minimize the cool off period.

Amed Mesa wrote:There is too much wasted energy in the design from the video posted. The use of the "rocket" effect is utilized in a manor to minimize carbon monoxide and smoke which would be better (not recommended) for indoor use, but not much use other than this. If you are soon going to build that cob oven, I would create it in a manor that allows the exhaust rocket flame to vent inside the thermal chamber, otherwise the rocket effect would be more of a novelty.



These ovens are thermal batteries in that they can store a large amount of heat and dissipate slowly. DO NOT USE CONCRETE! Cob is a good material in that is cheap, holds adequate thermal energy and not prone to structural cracking from heat, but it will need to be protected from erosion caused by rain. There are other materials you will find for a more permanent structure if you do some research of wood fired pizza ovens but they are more costly. You want to maximize your efficiency by utilizing as much potential heat as possible from the fuel source so do not copy the design from the video unless the novelty flame is what you desire. Because each of these ovens are hand crafted, baking feels more like an art. You can with experience triangulate the fuel mass with environmental temperatures to reach target baking temperatures so you can minimize the cool off period.

I agree, and I noticed the same thing.
I'm sure that's why the author stressed that it's not a Rocket Oven, but rather a double chamber oven.
With the volume of heat and fire coming out of the stack, it appears to be very inefficient.
I am assuming the advantage is in the extra mass to hold heat longer, although I have no idea how efficient regular wood fired ovens are, in comparison.

Here is a link to buy the plans for $25

Paul talks with Ernie and Erica about rocket mass heaters in this podcast: rocket mass heater podcast

They also talk about Ernie and Erica's double chamber cob oven plans.

Here's a couple of other ovens using this general plan.


https://skydrive.live.com/redir?resid=E1306005D407E60D!2079&authkey=!AE1Zjd4Uhpivgio




Regarding the waste heat issue:
It's definitely not a rocket mass heater; but it is a substantial improvement on a traditional earthen dome oven for cleaner burn, with minimal additional materials or building challenges.
A suspended, bottom-heated oven floor gives a different heat profile than a traditional masonry-floored oven. While the differences can be mastered, many artisan bakers prefer the traditional dome.

Wood-fired ovens are generally chosen for quality of food and cooking experience, rather than a theoretical maximum efficiency. For efficiency alone, I suppose you'd want a solar oven, or a microwave.

Best of luck with all your summer foods and fires.

Yours,
Erica W

I have been trying to find the answer to this question on the web, but haven't been able to find it. I live in Farmington Hills, MI... in the suburbs of Detroit... and I would like to take steps toward making our 1.75 acre lot and house more self-sustaining and clean. I absolutely LOVE this oven, and I wonder if I could build it in our 3 season sunroom. The floor is a concrete slab and the walls are wall-to-wall windows. You said that all cob ovens smoke at first, but with all of those window's... would that be enough ventilation? (5) 20"x58" openings and (3) 30"x58" openings.

It's too cold to gather in the sunroom in the fall and spring... so I am hoping the heat from the cob oven will help warm the space up a bit too.

Also, I bake artisan sourdough bread... and would love to have the wood oven to bake in during the holidays. Can the oven be fired in the fall/winter/spring? (That was supposed to be my original question, lol). We can get very cold and snowy here in Michigan.

Bumped for a Friend Big AL

Hi.
I'm investigating which type of oven I should build as my first cob project.
Reading a lot here and there I would like to ask something about the pro's and con's of a single and a double chamber oven.
If I understood this correctly the benefits of a second chamber is mostly a cleaner burn/ less smoke and a little less time to bring the oven to baking temp.

Better fuel efficientcy of which is spoken in the video seems to me comming only from the shorter timespan you need to pre heat the oven.
Or does the afterburning of the fumes in the chimney also contributes to the temp. in the baking chamber?
Its obvious it looses a lot of energy in the chimney.

Currently testing a rocket stove termal mass heater build out of cans and defenetly thinking about a RSTMH in combination with oven.

Thanks all contributors to this and many other forums for sharing your expiriences.

Attached my tin tinkering project.

I.

Ivar O. : Interesting project, though you will experience 'metal fatigue' very soon during your operation, I am very interested in the outside
RMH Temperatures that you record! I expect that you will also see scorch marks below the burn tunnel very early during its usage !

How and out of what materials did you build your Heat Riser inside your 2nd ''Barrel''? For the Good of The Crafts ! Big AL

Hi Al,

As you can see it kind of evolved from a pocket rocket to a RTMH.
I tend to to before I read a lot. Met some challanges as I went along.

The heat riser is also made of cans, double walled insulated cans. See pic below.
I used rockwool (cause it was free to me) and found that it isn't suitable for those temperatures.
First challenge.
I didn t get a good draft, probarbly because the heatriser is not long enough compared to the burn tunnel.
Challenge two.
And now the metal fatique, challenge three is, thanks for that, looring.
I wanted to build it all out of free, waste materials.

Gonna tinker on and make some adjustments and share what I find.

Thanks for the input.

In adition to previous post, it seems to me that the heatriser schould be longer and more narrow.
What are your thoughts on that?
The scroch marks you're right about.
It realy amazed me how high the temperatures get in this setting. I planned to cover it all in cob (the lower part) to avoid my board catching flame.
Maybe using a double wall insulated burn tunnel will be better and then cover it with cob.

My objective is to construct a small setup of this system for use in gardens, cook something or just enjoy the colder getting evenings outside.
I want to spend as little as possible and upcycle as much "waste" as I can.
A garden heater so to say.

Ivar O. : If one follows closely Ianto Evans' original plans for constructing a Rocket Mass Heater RMH and can scrounge most of the materials from waste,
or raw like clay from your near environment it is still possible to build a RMH for less than $100.oo U.S. This is good scrounging !

Consider going to Cobcottage to down load your PDF Copy of Rocket mass heaters with reports of over 100,000 RMHs built and working world wide, this
is ''The Book'' that most RMHs were built following, and 95% of all the new RMHs (that worked) were built from ''The Book'' !

After you have this book in hand -you can then come back here to your fellow Rocketeers, and expect that you will be using the same words to describe
a Rockets, Size(s) shape,and orientation of parts to themselves and the whole rocket !

Think of it as an investment that will save you Time, money, and hours of frustration in trying to 're-invent the wheel' !

I re-read your thread, What you really want is a Rocket cook stove, and one that is portable-kinda ! WARNING, I will be hooking you up to a video on
U-Tube, There is a tremendous amount of crap on U-Tube, use extreme caution if you go trolling there !

Your existing Rocket stove (-not a Pocket Rocket) Will evolve into something too heavy too be readably moveable ! My new recommendation is to do a
You-Tube search for 'LDS Prepper Stove' and then where he filled the space with dirt, use a 85% perlight 15% clean raw clay mix, or 80%
vermiculite 20 % clay mix The clay needs to be dug screened, cleaned dried and then the two dry ingredients are measured and then the clay is mixed
with water to make a thin pancake batter, THEN mixed with the Perlight or vermiculite, when you are done the mix should form into balls like popcorn
balls but fall apart if squeezed ! Then you just pack the mix inside your copy of LDS prepper's cook stove ! Don't for get to provide an air channel under
the Wood fuel,.

This build if covered up after every use should last you for years of outdoor use ! It is also a great stepping stone to building a RMH! For the Craft Big AL

Late Note : We, you and I have been guilty of high-jacking a forum thread a long way from the original topic, as a new be, this is not a big deal and I
should have caught it and had it moved My Bad, this will get moved to the Rocket stoves forum, and the thread title will remain the same ! A.L.

I have a question about the time lapse photo series in the link under the picture of the oven Erica posted. It shows many glass bottles being laid in the sand that's inside the base. Why is that? Are the bottles important in some way?

Kevin MacBearach : 1st, thank you for rescuing this thread, the about thread it was accidentally Hijacked, a all to common newbe mistake,
and I had perpetuated it ! And thanks for reminding me those time lapse photo's were there !

Hopefull this might draw a comment from Erica as she has strong feelings about bottle placement in cob ovens and in rocket Mass Heaters !

They are there partly as a type of insulation , perhaps it would be better to call them a Thermal break ! The Bottles encapsulation also serves
as a small memorial to the occasion when they were consumed !

At best this is a partial answer, You can get plans at E & Es site ::-> ernieanderica.info/shop !

The stone base or plinth is in a D.I.Y. Gabion basket, these can be very sturdy and can be used as heavy duty landscaping reinforcement

keeping entire hill sides from slipping away ! Hope this helps and is timely ! Big AL

Kevin MacBearach wrote:I have a question about the time lapse photo series in the link under the picture of the oven Erica posted. It shows many glass bottles being laid in the sand that's inside the base. Why is that? Are the bottles important in some way?

As Allen said, the bottles are insulation. The air they enclose is a poor thermal conductor. The bottles themselves are laid in a perlite/clay slip mixture, which is also an excellent insulator. We used them both under the hearth and around the dome.

We just did a big bake yesterday in that oven. From a single firing we were able to do 4 rounds of baking:
1) 5 loaves
2) 3 loaves + 2 baking tins
3) 2 challah loaves
4) pot of baked beans

This insulation performs very well (when coupled with adequate thermal mass).

I have very recently got the plans for Erica and Ernie's double chamber oven. I don't believe they talk about incorporating glass bottles in the base in these particular plans I have. I also like the way you guys did the foundation with the wire. So it looks like "smaller" stones used for filling? And what's the reason for the inner wire hoop, is it just more small rocks to reenforce the base? The pictures don't show what goes in there? Lot of curious things going on in these time lapse photos, such as the first pic looks like a drainage trench coming out? I can't imagine what that's for except if a pot of beans breaks in the oven maybe? Would it seep through the baking surface?

So you have two layers of brick, one regular bricks for thermal mass, and then your fire bricks for the baking floor. I never saw this extra step before, is this the more efficient techniques all in one oven? Impressive, I'd like to know more about these extra steps for the double chamber oven.

Kevin MacBearach wrote:I have very recently got the plans for Erica and Ernie's double chamber oven. I don't believe they talk about incorporating glass bottles in the base in these particular plans I have. I also like the way you guys did the foundation with the wire. So it looks like "smaller" stones used for filling? And what's the reason for the inner wire hoop, is it just more small rocks to reenforce the base? The pictures don't show what goes in there? Lot of curious things going on in these time lapse photos, such as the first pic looks like a drainage trench coming out? I can't imagine what that's for except if a pot of beans breaks in the oven maybe? Would it seep through the baking surface?

So you have two layers of brick, one regular bricks for thermal mass, and then your fire bricks for the baking floor. I never saw this extra step before, is this the more efficient techniques all in one oven? Impressive, I'd like to know more about these extra steps for the double chamber oven.

There's lots of ways of insulating. Bottles are cheap and available.
We filled the core of the gabion with urbanite and just put a layer of nice river rock on the outside. The inner gabion made it easier to manage the different materials.
This is a wet spot in our yard and has a French drain running through it. We put a rubble foundation underneath the gabion and hooked it up to the French drain. This also drains rain water from the roof.
The extra layer of bricks is intended to add more thermal mass. I was tired of mixing cob and bricks are dense and easy to work with.

So yes, there are a bunch of tweaks that we made to the basic design. Nothing revolutionary, but it's working nicely.

Is there any info on placement of bottles, how many, etc., to put inside the foundation?

I believe Erica mentioned spacing them about 1/4" apart, but that obviously can't be followed precisely given the shape of bottles and the shape of ovens. The more of an area they cover, the more insulating value they give, at the possible cost of weakening a structure. In a flat base, there is nothing to consider except compressive stress which bottles are perfectly shaped to absorb when embedded, but in oven walls you would need to ensure that they don't make the continuous outer layer of cob too thin to stand by itself and resist occasional impacts, or too disconnected from the inner layer.

Hi all,

I came a long way since last year, yes I bought the book and yes I red my eyes out and saw a million of Utube vids...

Here's a pic of my first serious attampy to build a RMH.
Can't wait to have it finnished and see how it performs.
Thanks all and Al.

Nice oven, Ernie. Isn't it the same as a Russian Stove but in miniature?

Not really. A Russian stove like the one shown is designed to absorb as much heat as possible from the fire's exhaust, though this one looks antique and not up to the efficiency of new ones, which control air supply and create a true secondary burn.

The double-chambered oven is just designed to burn cleanly and not leave smoke to bother the neighbors (or the users). It might get some extra heating from the secondary combustion, but that would be a side effect.

We just added a way to buy our plans directly through Permies,

Click HERE for the official Double Chamber Earthen Oven Plans

We've dropped the price a bit while we're transitioning to this new digital marketplace.

Getting ready to build a few more ovens this year, mostly in WA and ID.  I love seeing all the styles of ovens (and pizzas and breads) you are making out there.  

Happy baking!

-Erica

Trev / Glenn - Yes, Glenn is correct that our oven plans are a relatively simple oven designed solely for baking, not a mass heater.  
These are usually built as an outdoor kitchen feature.  
You may see similar, enormous wood-fired ovens in big pizza restaurants sometimes, or traditional restaurants that bake their bread and roasts in a wood-fired oven.  These commercial-scale wood-fired ovens are often built with fire brick or refractory cement liners, not traditional clay-sand earthen oven mix.  I've heard of one that was built by the restaurant family's grandfather, using stone.

Some Russian masonry heaters do include an oven, either a square side oven (as in your video) or a barrel-vault oven as the main fire box.  But what Russian masonry stoves are really famous for are the heat-trapping channels around/after the firebox, and usually a bed platform on top where someone can bask in the warmth stored in the bricks.  Russian "fireplaces" are one of the better-known models of masonry heaters, sometimes called "accumulation heaters" in Europe.  There are a lot of distinct versions of accumulating heaters from different places, including our rocket mass heaters.

Our oven plans are designed to store several hours' worth of heat inside for even, artisan-quality baking, and to reduce smoke compared with simpler one-chamber dome ovens.  Aside from that, they really are a simple, relatively primitive outdoor oven, not that complicated to build or operate.  

We usually heat indoors with a rocket mass heater, optimized for efficient heat.
Our outdoor oven is the big wood-eater for pizza parties (it will burn the big gnarly pieces that are harder to chop down for the rocket stoves).  We use it more seasonally, like you might use a barbecue.

-Erica

Hello Ernie,
I was collecting clay to make a cob oven with a chimney and then saw your video of your double chamber oven.
Please could you tell me, is the door to the baking chamber set behind the flue please or in front of it?
It looks like it's behind.
I live in a village in Catalonia where they make cocas, a very thick pizza, sometimes covered in sweets, they hand them out at festivals.
I wanted to return the favour and make thin pizzas for my neighbours at festivals, they have a lot here.
Planning a 34 inch one to accommodate the pizza and bread making.
The base is already popping out of the ground, as it's part of a ruined house in the garden, so just strengthening that up first before I add my lower thermal insulation layer of bottles and cob.
I will definitely add a burn door at the front, that's a great idea. Is it a steel door?
Would you recommend the best length for the passage from the dome to the front burn door please for a 34 inch cob oven, I'm keen not to pollute the festival areas with smoke, my garden is right next to the square where they hold them.
Thank you.

Hello again,
Just rewatched the video.
I think I understand.
The bottom of the chimney looks like it's set in the centre of the front chamber and the baking door sets in flush behind it.
Am I understanding that correctly?

Amedean Messan wrote:There is too much wasted energy in the design from the video posted.  The use of the "rocket" effect is utilized in a manor to minimize carbon monoxide and smoke which would be better (not recommended) for indoor use, but not much use other than this.  If you are soon going to build that cob oven, I would create it in a manor that allows the exhaust rocket flame to vent inside the thermal chamber, otherwise the rocket effect would be more of a novelty.  



These ovens are thermal batteries in that they can store a large amount of heat and dissipate slowly.  DO NOT USE CONCRETE!  Cob is a good material in that is cheap, holds adequate thermal energy and not prone to structural cracking from heat, but it will need to be protected from erosion caused by rain.  There are other materials you will find for a more permanent structure if you do some research of wood fired pizza ovens but they are more costly.  You want to maximize your efficiency by utilizing as much potential heat as possible from the fuel source so do not copy the design from the video unless the novelty flame is what you desire.  Because each of these ovens are hand crafted, baking feels more like an art.  You can with experience triangulate the fuel mass with environmental temperatures to reach target baking temperatures so you can minimize the cool off period.

good analogy couldn't agree more. My wood oven does not store much heat energy. Storing much heat energy and giving it off after cooking is an added waste. No need to preheat very long time also. Which is another waste of energy.

Hello again,
I have seen lots of cob ovens bursting flames out of the front of them, so a chimney seemed logical to me and then I saw this video whilst I was planning it, though my knowledge is very weak in this area.
How would you exhaust rocket flame to vent inside the thermal chamber please?
I haven't started on the cob dome yet, I am still strengthening the foundation.
Are chimneys completely unnecessary on cob ovens in your opinion?
The smoke bothering my neighbours and the idea of the emmissions being described as cleaner attracted me to the chimney idea.
I am learning though and happy to hear all superior knowledge, I only know how to sculpt objects and balance them.