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.

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...

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.