Inside A Tin Can Rocket Stove

This is an inside view of a rocket stove. The center can is the combustion chamber.  The side can is the fuel magazine.  The fuel magazine has a shelf for fuel to rest on.  This shelf allows air to enter from below the fuel.  It is this “L” shape design with air entering from beneath the fuel that makes a rocket stove a “rocket stove.”  Both of these cans are 3″ diameter by 4-1/2″ high .   The outside can is 6″ D x 7″ H.  The top of the large can has vents.   After several smokey fires, we found that (3) 1″ deep x 3.25″ wide vents reduced smoke pollution, significantly.

Rocket stoves can be made with adobe (dirt), bricks or metal.   Tin cans were convenient for my son (age 11) to work with for his science fair project.   Tools used were a hacksaw to score the side of the cans enough so that curved tin snips could cut the holes that another can would fit in.  We used straight tin snips to cut the top vents.   You can get by without straight tin snips, but it is more work.

Since the cinder block rocket stove experiment, we have solar dried twigs in order to reduce pollution (smoke).    Smoke is uncombusted fuel.  That wasted fuel (smoke) is also a major health hazard for the over 2 billion people who have no choice but to cook over a fire.  Over one million women and young children die each year from respiratory diseases caused by smoke.   Countries have been ruined because they don’t have enough trees to keep the topsoil from blowing away.

This simple stove, designed by Dr. Larry Winiarski, is saving lives in 3rd world countries.   This simple stove is also a great low-cost solution for camping and being prepared for extended power outages.

High winds and earthquakes are common causes for electricity to be knocked out.  My last power outage lasted just a few hours in December 2011.  It was due to high winds that were strong enough to blow a roof off in my neighborhood.

The rocket stove is a free and easy solution for cooking.  If my electricity ever goes go out for an extended period of time, I will be able to cook up the contents of my freezer before it goes to waste.   In the meantime, my son has enjoyed tending fires and cooking food for family and friends.

I hope this post encourages you to make your own rocket stove.

The very top can inserted into the center turned out to be unnecessary.  It has been discarded it.  The original lid of this can is placed as a lid over the insulation.  This rocket stove was insulated with volcanic rocks because it was a curb-side freebie and not as messy as ashes to work with.  They are NOT recommend for insulation because rocks absorbs heat which robs heat from the cook pot.  This means I need to use more fuel to cook my food.  That said, we found that the retained heat stored in the lava rocks radiated for at least an hour after the fire burned out.   Because of this, I have used the rocket stove as a space heater AFTER the fire is completely out.  If you want to use rocks instead of ashes, then only use lava rocks.  Regular rocks, when heated up, can cause serious injury.

The most fuel-efficient rocket stove is insulated with a low-mass material.  Low-mass insulation traps heat because it is poor a conductor.   This means that heat has trouble conducting (moving) through it.   This trapped heat causes the food to cook with less fuel because nearly all the heat is absorbed by the cook pot and food.

The best free low-mass insulation is ash.  If you don’t have any, it can be gathered from barbecues at public parks.  If you are going to buy insulation, then buy perlite (an amorphous volcanic glass).  It is second best compared to light-weight refractory bricks.  The bricks are home made with clay and burn-out material.    Other good low mass insulation materials are pumice rock or vermiculite.   Notice that low-mass materials are light-weight due to lots of tiny air pockets.

These two rocket stoves are identical except for the size of the fuel magazine and combustion chamber. The left was made with (2) 3″ D cans, and the right was made with 4″ D cans. Each stove burned exactly 8 ounces of fuel for about 30+ minutes. They both burned up the fuel completely with very little leftover char. The results were that they both work, but it was easier to tend the fire with the the 4″ diameter cans.  The small combustion chamber chokes up faster due to ash blocking the air intake.

Dr. Winiarsky recommends a 4″ diameter combustion chamber.   I knew this before my son started his experiment, but thought it would be good for him to discover that for himself and also get some practice at nursing a struggling fire.

Hey look! I have a two-burner stove in my fireplace!  This was the first time my son fired up the tin can rocket stove.    It was cold and rainy for days so I finally let him test it in our fireplace.   My son boiled water first and fried eggs his first test run.  We were fine, but my husband got a headache.    So we were banned from using the rocket stove in the fireplace until we resolved the smoke emissions.  Both my husband and I are both allergic to smoke and prone to headaches from it.  There wasn’t much smoke or I would had a headache, too.    We had tested it a lot since this day.  After several widenings of the tops vents we are happy to see less smoke and ready to test it in the fireplace as soon as we get permission.

Here is a video by LDSprepper on YouTube on how to make a tin can rocket stove and here it is all fired up.  We like this guy’s enthusiasm for rocket stoves.   We share that enthusiasm until the combustion chamber has enough ash to block the bottom vent.   Then we are done cooking whether we wanted to be or not.    Grr.

All fired up! Look closely. Notice the fuel is on a shelf so that air can enter from underneath.

I can and have knocked out the ashes to start a new fire, but I do not like turning it upside down when it is that hot.   We designed a solution, but my friend wanted to bake a special Easter bread in the can I just got for this project!  I will post the new design as soon as I can.

Additional Resources

If you are ready to build, then I suggest you use 4″ D x 7″ H can on the side so the fuel magazine and combustion chamber can be one piece.  Place a 4″ D x 4″ H can on top for the chimney.  The cans fit into each other like the original design on the top of this post, except they have switched places in order for the spent fuel (ashes) to be dumped out of the rocket stove from the combustion chamber by way of the fuel magazine.   This new design is better because it is easier to remove spent fuel from the side than from the top.    I have found that turning a rocket stove upside down to dump ashes is awkward, uncomfortable and inconvenient, if it is still hot.

If you want more technical information about rocket stove, visit my Cinder Block Rocket Stove post.  It is loaded with links to my favorite technical specs.

Due to the new rocket stove design, I am now in the habit of looking for food that comes in 4-1/2″ x 7″ tin can.  Winco and Stater Brothers Market sell vegetable cocktails and baked beans in this size can.  I have a small family so what works for us is to use the vegetable cocktail as a base for a soup, and to take the baked beans to potlucks.   Fortunately, I attend a lot of potlucks in the summer and baked beans are perennial favorite!   I do not need to buy the 6″x7″ can (aka #10 can or coffee can) because restaurants will give them away FREE.

Warning, the danger of rocks exploding in a fire is a serious issue that you need to consider if you are going to use rocks for insulation.  For more information, I suggest reading about this phenomena here:   They describe exploding rocks from first-hand experience.  Yikes!

* * *

By failing to prepare, you are preparing to fail.
Benjamin Franklin

UPDATE April 3, 2013 – I am sorry I haven’t taken the time to add updated posts on the rocket stove.  I will, but need to focus on yard work until the weather heats up to unbearable.

In the meantime, let me tell the results of dozens of test fires done on five slightly different tin can rocket stove designs.    The best burning and easiest to use rocket stove has a 4″ diameter x 4-1/2″ tall can for the fuel magazine (same as above).    The combustion chamber works better with a 4-1/2″ diameter x 7″ tall can.   This rocket stove has a grill made of wire fence material instead of top air vents.  This grill is the pot rest.

I have over a dozen photos of our new rocket stove with step-by-step directions on how to make it.    We have made several and plan to hold workshops at the park for those interested in making their own.    If you plan to attend, you may bring your own cans or purchase them from me.

Now that I’m happy with my rocket stove, I want to make a rocket oven that fits inside of my fireplace.   I bake my food in a solar cooker year round, but want the option of heating my home while cooking in my fireplace.

It will be similar to this low mass design, except only big enough to bake one casserole or a large pizza:

* * *

“Education is not filling a pail but the lighting of a fire.”  ~William Butler Yeats

About Hemet Sunshine

I am a homeschooling mom living in Hemet, California. I am interested in building a better community for the ones I love.
This entry was posted in Can & Wire, Rocket Stove Cooking. Bookmark the permalink.

6 Responses to Inside A Tin Can Rocket Stove

  1. Sandi Hughes says:

    I love this project! We need this kind of thing here in Anza for our recycle progects. I would love for you to come and teach us this project for Anza Earth Day, May 12th. Any chance you might consider it?

  2. Hi – any tips on measuring out the hole on a curved surface?

    • We are in the midst of making 8 rocket stove that are slightly different from each other to use in my son’s science fair. I just start starting taking step-by-step pictures on how to make the rocket stove the easiest way.

      For measuring the hole on the side of the can, we traced the base of the can on cardboard from a cereal box. The cardboard is thin enough to bend over the curve, and thick enough to be a good guide for tracing with a fine tip marker.

      Score the center of the hole with a hacksaw first, then use curved tin snips to cut the hole.

  3. Thank you for sharing your project. You make it easy to understand with the pictures and detailed explanation.

    • You are very welcome.

      Eventually, I will put more pictures up. We are currently working on a rocket oven. We spent the last couple weeks gathering local soil to render clay. That went well, but we are surprised how much time it has taken to make paper pulp. We stopped after processing 5 pounds. Now we are going to process 5-10 pounds of horse manure because it is less labor and time intensive. After the clay, sand, and fiber (aka fiber adobe) is mixed, my son is building a portable rocket oven that he can take to the park for pizza parties. I will post pictures after science fair. PSUSD Science fair is February 6th this year.

      The paper pureeing put us behind schedule and I found out last week science fair is a week early!

      We are little stressed out.

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