Jeremy Cash

The best thing to do with a good theory is test it. Take lots of pictures, documentation, etc. and share your findings with us.

If you do some thermal radiation calculations you might find that one barrel will already put out many times more btu's than a traditional wood stove. With two barrels you will likely be standing outside since your house may be closer to the temperature of the sun...

It's good to see you have approached this with an engineering perspective. To loosely answer your questions:
1. I haven't seen anyone mention a need to address the condensed water vapor.
2. The ash clean-out is usually in the heat bench, however, not needed to be cleaned much because there isn't much ash due to complete burning of the wood smoke and ash.
3. I see how oxidation would be a concern, however, I have not seen anyone mention it to be a problem.

Although I'm not really answering your questions, I hope this is better than nothing.

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Let me illustrate. When designing your Rocket Stove each section should be considered separately.

Section 1. is the Fuel Source, in our case, wood.

Section 2. is where the fuel and air is mixed. This is where the size does not have to equal the heat riser. According to the Bernoulli Principle, as the pressure decreases(smaller opening), the speed of the fluid, in our case air, increases. Thus increasing "rocketiness". I used equations to prove this as well as tested it. The greater the temperature is in this section the greater the rocket effect.

Section 3. is the Heat Riser where we are taking advantage of the heat expansion of air. This is the work-horse of the stove. This is where the size should be as large as you can make it. This variable strongly effects the rocket effect.

Section 4. not shown would be the barrel which is radiating heat into the room and cooling the air.

Section 5. would be the Heat Bench where we extract even more heat and store it like a capacitor stores electricity for release.

Section 6. would be the exhaust where it finally leaves the building. This section of pipe also can be any size and will not have an effect on the intake. This is because air is compressible. If you have a 4" exhaust versus an 8" exhaust, the main variable effected is the pressure at that point in the flow.

Breaking the stove down into its individual sections and tackling each separately will help you to maximize the rocket effect while maximizing the dollars in your wallet.

I hope this helps.

After reading some posts I realized I may not have made it clear enough in my own post.

The diameter of the heat riser is the primary variable of the "rocket" effect.

One of the two "engines" driving the stove is the heat riser. A bigger "cylinder" produces more power.

The second "engine" is the cooling of the air at the heat barrel causing a bit of a siphon effect. I'm sure it can be quantified but I haven't discovered that equation yet.

The "stack effect" or chimney effect is accomplished within the heat riser. The main "force" behind the rocket effect is the difference in temperature between the inside of the burn chamber and the outside air. Even though the heat riser is only approximately four feet tall, it is doing most of the work. That and what I assume to be a siphon effect (haven't figured out the equation yet) of the air being cooled at the barrel is adding some force to the flow.

So to answer your question, you must have a "chimney" or heat riser to accomplish the air movement. Or simply put, no. It will not work without a "chimney".

Some equations to help make the most of your barrel.

Area of a circle = pi x radius^2

55 gallon drum diameter(d) = 23", radius(r) = 11.5"

To make the inside diameter match the outside diameter within the barrel use:

2a + b = radius

I decided to use a 10" heat riser by starting with 23" - 10" inside diameter which leaves 13" which breaks down to 1.5" of insulation.

10" + 3" = 13" for the diameter of the outer wall of the inner pipe. I used a 7" pipe connected to a 6" pipe to make the 13" diameter pipe and filled the space with the insulating material.

The 5" remaining radius totals a 10" diameter outer pipe.

Even though we are dealing with a circle, pi and the square cancel out and you are left with a simple linear equation.

Before I designed my Rocket Stove I consulted with my engineer brother-in-law who guided me in the right direction to understanding exactly what makes a Rocket Stove "rockety". Because I am ADHD I hate wordy posts so I will try to keep it simple. My hope is to help everyone understand what is happening inside the Rocket Stove so they can improve their own designs. I am in no way a math wiz and so I plugged these formulas into an excel spreadsheet and played with the numbers so I could make the most of the stove.


The primary factor driving the force within the rocket stove is the "stack effect". The larger the heat riser, the faster the flow will be. The other is the difference in temperature of the fire box and the outside air.

In my stove I used fire brick, a 10" heat riser 1.5" thick and a 55 gallon drum.

I used Paul's portable rocket mass heater design and made some minor tweaks.

I discovered with trial and error and calculations that the size of the intake is not as important as the size of the heat riser. If you take a look at the "ventury effect" you can see that a smaller opening will actually help increase the air speed over the burning sticks also improving the "rocketiness".

I chose a 10" heat riser by using a basic formula based on the 23" diameter of the drum. In the flow equation A = the Area of a cross section of the heat riser. To prevent a bottle neck past the heat riser if I use a 10" heat riser + 1.5" of insulation totaling 3", the remainder is 10".

I said I will keep it short, I hope this helps get some wheels turning. Feel free to comment. Thanks. I will try to post pictures later. Thanks to those who introduced me to an efficient way to heat things up.