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Double Chamber Cob Oven

Chris Ocampo


Joined: Dec 22, 2011
Posts: 4
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!
Klaymen Strife


Joined: Oct 23, 2011
Posts: 23
I am also interested in this.
Len Ovens


Joined: Aug 26, 2010
Posts: 1275
Location: Vancouver Island
    
  15
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.
Ravi Gautam


Joined: Dec 30, 2011
Posts: 9
Chris Ocampo wrote:Hey Ernie, love your oven, this one.
http://youtu.be/TvrUrnEIQoo
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!


Nice link...
Ernie Wisner
volunteer

Joined: Oct 16, 2009
Posts: 788
Location: Tonasket washington
    
  23
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.

Need more info?
Ernie and Erica
Wood burning stoves, Rocket Mass Heaters, DIY,
Stove plans, Boat plans, General permiculture information, Arts and crafts, Fire science, Find it at www.ernieanderica.info


Marcus Harden


Joined: Jan 12, 2012
Posts: 9
Location: NE Oklahoma
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!
Cj Verde


Joined: Oct 18, 2011
Posts: 2406
Location: Vermont
    
  44
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.


My project thread
Agriculture collects solar energy two-dimensionally; but silviculture collects it three dimensionally.
Ron Hailey


Joined: Jan 13, 2012
Posts: 4
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.
Amedean Messan
pollinator

Joined: Nov 11, 2010
Posts: 768
Location: Burlington, NC - Woodland, Clay - Zone 7
    
  24
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.


Those who hammer their swords into plows will plow for those who don't!
Ron Hailey


Joined: Jan 13, 2012
Posts: 4
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.
paul wheaton
steward

Joined: Apr 01, 2005
Posts: 14879
Location: missoula, montana (zone 4)
    ∞
Here is a link to buy the plans for $25



sign up for my daily-ish email / rocket mass heater 4-DVD set / permaculture playing cards
Suzy Bean
steward

Joined: Apr 05, 2011
Posts: 940
Location: Stevensville, MT
    
    8
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.


www.thehappypermaculturalist.wordpress.com
Erica Wisner
volunteer

Joined: Feb 10, 2009
Posts: 720
Location: Okanogan Highlands, Washington
    
  85
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


Play with nature, make nifty stuff:
www.ErnieAndErica.info
Jenny Bedford


Joined: Sep 14, 2012
Posts: 2
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.
 
 
subject: Double Chamber Cob Oven
 
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