Build-a-RocketStove

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Make a Rocket Stove for Emergency Cooking Outdoors by Charmaine R. Taylor A Rocket Stove is simply a coffee can body with a 90 degree elbow pipe, or food cans, used as a chimney and throat. Insulation is placed around the chimney to keep maximum heat going to the bottom of your cookpot. The magic of this little stove is that just twists of newspaper and small twigs and scrap wood are used for fuel. If you lose power, don’t have propane or other fuels handy, or simply want to cook out doors then this is the stove for you. There are many designs for stoves like this; scouts, survivalists and outdoorsmen have experimented with low mass type cookers for years. How I developed the Coffee Can Stove a.k.a. “Rocket Stove” I originally learned of rocket stove cookers through Barbara Kerr, of the Sustainable Living Center in Arizona, when she and I were producing her Solar Wall Oven booklet.* Barbara is in her 70s now and has been living and cooking off-the-grid for over 25 years. She personally uses her own rocket stove to make meals and heat water, plus she teaches others to build and use them. Barbara explained that the original “Winiarski Rocket Stove” she uses was developed at the Aprovecho Research Center in Oregon by Dr. Larry Winiarski. This stove is made from a rectangular metal, 5 gallon cooking oil can. I began searching for a metal food oil can to construct one as she described. Absolutely no local restaurant or supplier carried metal food cans, or any suitable thin walled cans, so I was forced to improvise, and eventually developed this coffee can version. ( Several months later I learned Aprovecho had also designed a coffee can version too.) Metal cans in the 5 gallon size are difficult to locate anymore as most commercial food containers are plastic. However, you may be able to find 5 gallon food oil cans in your area and be able to build a larger style rocket stove from the instructions given here. I also haunted the local hardware store, thrift stores and other places to find low cost materials to build a stove. A new, empty 5 gallon metal paint can was considered, but punching a hole through it was too difficult. I experimented with a small, rectangular 3 quart olive oil container, and a then a 2 lb. coffee can. Since it was easier to remove the lid on the coffee can with just a can opener, I developed

that idea first, as well as creating a small clay stove version. The clay design, also described in my booklet “Build A Rocket Stove Cooker” is easier to build in some ways, and requires fewer tools, but test results from Aprovecho prove that metal cookers heat food faster, and use fuel more efficiently. Rocket Stove Designs The basic materials needed to make a Rocket Stove are coffee cans, fruit and vegetable cans or a 90º metal elbow pipe. These thin wall elbows are galvanized and they will off-gas when heated initially. • 26 oz. coffee can • 3” diameter 90 degree metal elbow pipe, or food cans • metal gas stove grill or bent wire/rebar • aluminum foil patties for insulation (save used foil) • or, wood ash for insulation • metal skirt or wind shield Tools • large drill bit with electric hand drill, or large nail to punch pilot hole • tin snips, preferably R and L cutting Your local hardware store should have metal parts in the plumbing department. Purchase a formed 90º metal elbow. These come in different neck widths from 2.5” to 6” or more. The 3” one I purchased cost $1.62 and was a good size for the coffee can, and all the coffee can photos shown here use the 90º metal elbow. The advantage of an angled elbow is that no additional hole cutting is needed, just a single opening is made into the coffee can. In addition, these elbows may last longer than food cans. But with daily use any metal materials used may burn out in one to three months. Making A Stove An opening must be drilled, or cut, in the coffee can to fit the chimney throat. If you use a large juice can for a chimney, a hole must be cut in it too, where the smaller throat can will be inserted. This is the most difficult work, and care needs to be taken with sharp metal edges, and in using tin snips or drill bits. Step 1– Hole cutting. Cut a round hole in the coffee can, and the inner chimney can, the same size as the opening of the throat can. If a soup can will be used for the throat then both holes will be made to fit the soup can. Trace a circle the size of the throat can onto the coffee can first.

To make sure coffee can and chimney can are aligned cut coffee can hole first, then place one inch of insulation in the bottom. (Crumple recycled aluminum foil and pack the base of the coffee can.) Set the chimney can inside, then trace a line onto the chimney by running a felt marker around, at an angle, using the outer coffee can hole edge as a pattern. An initial hole can be drilled with a large pointed bit, or a large nail. The lower edge of the hole should be one inch or more above the bottom of the coffee can. The top of the chimney needs to be slightly below the coffee can rim (1” is adequate). You do not want the chimney to be more than one inch below the rim as heat will dissipate away from the cook pot and waste energy into the air. Also the chimney must not be higher than the rim of the coffee can. You can always snip around the top of the chimney and bend the edges down so it is below the coffee can rim. Step 2-Fitting the Chimney. A 90º metal elbow is easier to install if the opening is cut to fit exactly. The coffee can wall will support the weight of the elbow. You can always snip the top of the elbow pipe so it remains below the coffee can rim. The height of the body will determine how tall the chimney must be. Most metal elbows are galvanized and once fitted in place should heated several times to burn off any gases. You can do this when you are testing the stove, but before cooking food you will actually eat. In addition a pure clay “slip” ( just clay and water mixed to the consistency of cream) can be poured through the metal elbow to leave a thin coating. Upon heating this will form a protective interior coat, and can help the metal elbow last longer. If you use a tall juice can for the chimney, and have cut a throat hole, you can assemble the stove easily. The juice can will sit on top 1/2” to 1” of insulation in the coffee can. Remove both ends of the soup can and any paper wrapper. With the chimney and stove holes lined up, fit the soup can so it passes into the coffee can, then into the juice can. The soup can will stick out from the coffee can, and serve as a loading area for more fuel. The juice can will support the cook pot, eliminating the grill ring, but only if several holes have been punched around the top two inches to allow good ventilation. Step 3– Insulation. Temperatures inside the chimney will exceed 1100º F, effectively burning wood completely and reducing smoke. You need to pack insulation underneath and all around the chimney. It is important to insulate the

bottom of the coffee can to prevent overheating and burnout of the bottom. Use wood ash from a fireplace if available, this is an ideal lightweight material as it has already been consumed, and will absorb no heat from the fire. Crumpled tin foil is the next best solution, packed tightly all around and fill the coffee can. Don’t use sand or earth, or any heavy mass material for insulation as it robs heat from the chimney.

Using the Coffee Can Rocket Stove Practice, and Safety First! The coffee can stove takes a bit of practice before you feel confident you can make a whole meal. The first time I used my clay stove I overloaded fuel in the chimney and created a roaring bonfire, flames shot out the throat and chimney top by a foot or more! The first rule is to practice on a windless day, in a semi-protected outdoor area where no flames or float-away newspaper scraps can start a fire on your roof, dry grass, garage, or any other structure. Have a full water bucket or hose at the ready to douse any runaway flames. Use less material, not more, when you begin. It’s easier to re-light the fire several times than deal with panic. Use an Insulated Base Place the coffee can stove on an insulated base, such as an overturned cookie pan, some bricks, or set on your BBQ grill as shown in the photo. Enough heat is generated that a stove sitting directly on a wooden picnic table or porch can char the surface. This is why you need insulation in the stove bottom. A BBQ grill is also good for catching any small burning twigs that may fall out, or dropped matches, and for holding twigs and twists to be used for fuel. Also, having the stove elevated for use is easier on your back. I sit on a small footstool, Barbara Kerr uses a lawnchair, with her rocket stove placed on a low table at comfortable reach. A fancy gas powered BBQ or a simple habachi can serve the same purpose.

Building the Fire Use dry twigs, wood scraps and paper twists. Scraps should be no longer than 4” or 5” or thicker than your finger. This method is similar, in a miniature way, to a campfire. You will want to have a good supply of thicker and thin twigs, and several sheets of newspaper, torn and crinkled into twists as big as the twigs. Have a thick stick for pushing paper and twigs around to protect your fingers from flames. Or use an old BBQ fork or other utensil. Crumple a piece of newspaper into a cone shape, and place in the bottom of the

chimney. Make a teepee of thick and thin twigs around it; 5-7 pieces should be enough. Lay 2-3 twigs and paper twists in the throat. Light the fire with a twist at the top of the chimney, or through the throat. A very easy way to begin fires is to use cardboard tubes cut from paper towel or toilet paper rolls. Stuff the tube with twists, twigs and wood pieces, and set upright in the chimney. The fire will be directed straight up to the bottom of the pot, and you can concentrate on keeping the throat fed with new fuel as needed. Once the fire is started place the pot support (a bent wire or grill) on top the coffee can, place the cookpot on the grill, and surround with the skirt. You can also practice without the skirt at first until you feel skilled enough to feed the fire, stir the food, etcetera without bumping the skirt or trapping your fingers. The fried egg example shown here used no skirt, and took six minutes to cook on a windy day. When egg frying was repeated inside my sheltered barn it took only two minutes without a skirt. Cooking larger pots of food, or when using lidded pots, the skirt is more important to capture all the heat and gases surrounding the pot. I initially began my stove experiments without using skirt around the pot, and while it takes longer to cook a hamburger you are better able to feed wood scraps through the top and see what is happening in the chimney. But for best results a skirt, or 3/4 surround wind protection wall, sitting on the BBQ will help you cook faster. Using a tight fitting lid over everything you cook will capture more heat also. Thin metal pots work best as they transmit more heat to the food. Avoid ceramic pots entirely. Alternative Designs– What to do if you don’t have large metal cans or aren’t able to cut holes in metal, or have no tools. One design about the same height as a coffee can uses an all clay/sawdust or clay / lime/sawdust slurry poured into a cardboard box form so the body is made without cans. Since I experiment with alternative building materials such as earth, sawdust, woodchips and bagged hydrated lime* I wanted to test these materials to make a few clay ovens. Tiny Redwood and Madrone woodchips were used as filler instead of sand, and mixed to make a clay slurry of very thick “batter” consistency. I used an 24” high by 12” x 12” rectangular cardboard box, and poured a slurry base one inch deep, then lightly pressed in the metal lid removed from the coffee can, and let it dry for a day. I cut a hole for the throat in the cardboard box and also into the side of a 18”x 8”x8” cardboard carton. The carton was positioned

inside the box and a 15 oz. can was pushed into its side about an inch. The inner carton was then sand filled. I poured slurry into the space between the box and the carton until it was full and level to the rim of the carton. (Any oblong form, such as a lidless one gallon olive oil can, could be used to keep the chimney space open.) Slurry is dense and heavy and a thin cardboard box will bulge and split, so use a thick walled box or brace all four sides with cinder blocks for a few days (which I did on my first design and it worked.) This form will need to air dry for a week or two in a sunny spot. The outer cardboard box form can be peeled away when the slurry has set up a bit to aid in faster drying. Once the clay stove is dry, pour the sand out, and peel away the inner carton, or just leave it, then fit the juice can fitted as the chimney. Tin foil is then packed around the can to insulate it from the clay walls. Keep as much insulation as possible between the chimney and the clay walls. Clay is a high mass material which will absorb heat as it travels up the chimney, robbing temperature from the cook pot. But, for people who may not have coffee cans, or cutting tools and aren’t physically able drill or cut holes by hand this is a very simple solution. Also, this stove is sturdy, and won’t tip over easily. If the chimney or throat burn out, simple replace with new cans. My personal experience is that many people don’t have the physical hand strength, especially women, to cut holes in metal cans. The clay stove, therefore, is much easier to build, and if necessary the inner surface could be packed and lined with many layers of tin foil to form a faux chimney. Clay and Elbow Pipe Stove Another alternative design uses a heater vent pipe with a built-in elbow, so no cans are needed. I found an unused one in a junk store for $2.00 and used it as a single chimney and throat. Because I was concerned it was galvanized metal I coated the entire surface with clay slurry and let it dry first. I did not join the pre-formed lip edges together, as the chimney then would have then been too narrow at the top, so I used a 4” strip of wire mesh, wrapping it over the top and bottom of the chimney, and plastering it with clay to make a solid semi-cone shape. (see diagram)I placed this chimney in a tall cardboard box and filled around it with clay/woodchip slurry. After drying I added more thick slurry by hand to finish around the top and throat. While taller than a coffee can cooker, and different than a Winiarski stove, the 45º throat angle seems to work just as well. And, it has the advantage of easily seeing into the fire base while cooking. When I first began testing and cooking with this particular stove it was helpful to be able to see the fire and determine how

much paper or wood scrap needed to be added. This is not the most fuel efficient stove because the clay body robs heat from the fire, but I like this design. Clay Slurry Mixtures Clay plus sand, or other fillers, can make a rock-hard liner for your stove chimney and for the body itself. Clay can be dug up from your yard or from road cut construction areas where the yellow-gold color of the earth reveals clay. A slurry can be made with clay and water mixed in a bucket, or just left to soften in water for several days before blending. You can use a paint stem mixer on a 1/4 hp. hand drill, or insert an old hand mixer beater. Or, softened clay can be hand mixed using a garden fork or other digging tool. The woodchip or sand/clay mix can sit overnight before using so the woodchips are thoroughly coated and wetted. Protect the stove from rain it’s drying and the result will be a lightweight, very hard walled stove that costs nothing to make. Hydrated lime used for mortaring can also be used in a 1:3, lime:clay ratio. In fact when you mix lime and clay it forms a mild strength natural cement, also known as Roman cement. Sand or other fillers can be used with the lime and clay, as long as the material is not easily combustible. *Note: Use caution when handling hydrated lime or quicklime, always wear gloves and eye/face protection. Heating Water Test your ability by heating a cup of water in a small metal pot with a lid. Pots will blacken easily on the bottom, and washing off the soot isn’t necessary, so use old pots. (I purchased several small used pots and lids at a thrift store just for rocket stove use, but containers made for camp cooking and open fires are good too. Avoid pots with flimsy plastic handles.) Get the fire ready to start, place a small temperature gauge in the pot if you have one, and light the fire. Water will heat to over 150º F in a minute or two, and will continue to rise if kept covered. Give the fire a full five minutes, feeding twigs and paper as needed, then check the temperature. These stoves can also pasteurize water in small quantities for safe drinking. A Water Pasteurization Indicator ( WAPI) device made by Solar Cookers International sits in the pot and indicates when safe temperature has been reached, 158º F. These devices cost $5. each, and come with instructions to make your own. You do not

have to boil water at 212º to pasteurize it. You can save on fuel and time by using a WAPI to help make safe drinking water at a lower temperature. Cooking off the Grid You can make pancakes, fry small pieces of meat, simmer one pot dishes and even bake bread with a larger, covered lid version of a rocket stove. Boneless cuts of meat will cook faster, of course, and be careful handling all raw meats, raw eggs and other foods to ensure they reach proper temperature to kill organisms. Debone and cut up chicken in very small pieces, and chop vegetables finely. Ramen noodles, rice noodles, and soups cook quickly, as does oatmeal, and other instant foods. Dry rice and water can go into a pot and be brought to a near boil, then removed from the fire, with the lid still tightly on, and placed in a haybox to continue cooking. Seasonings can be placed in at the start for more flavor. Vegetables can be added to the rice, soup, or casserole at the start, and left to continue cooking using retained heat.

Hayboxes A haybox is simply a cardboard box stuffed with insulating materials such as newspapers, straw, or old clothes. The cook pot is wrapped in an old blanket, wool clothing, or other non-plastic wrapping, and placed in the haybox. More insulation material is packed all around and the pot is left continue cooking from the retained heat. You can check the food after an hour, or half hour, and test doneness. Essentially this method is similar to a slow cooking crock-pot. Tests have shown use of a haybox combined with rocket stoves saves time, fuel and increases overall efficiency. Foods also taste better when slow cooked, and no time is spent tending pots. For food safety, do not let cooked foods drop below 140º F, or sit more than four hours in the haybox. Getting Started You may want to made several stoves if you have a larger family, and each stove can be assigned for different meal needs. Eggs can be cooking on one, bacon on another, while water boils for coffee, tea and cereal on another. And once food is cooked, a pot of water can be placed, a bit more fuel added, and you’ll have hot washing up water when the meal is over. Since the fuel burns so completely there are no hot coals left, and only a bit of black paper ash. Let the stove cool, tap out the debris in the chimney, and you are ready to cook again. For some reason men initially like this stove idea better than women. Each time I

have demonstrated the stove women are not convinced until they actually see something cooked successfully. It is hard to believe this small stove can be so efficient with so little fuel. But it is true. We are so used to electric or gas ranges, large camp fires, or propane fired stoves for cooking needs that the simplicity of this method is hard to believe. But, it is important to maintain a variety of methods to prepare food. Solar cook boxes and hayboxes are two more ways to expand your ability to prepare meals. Hayboxes were used extensively to cook foods during WW2 when kitchen stoves only had fuel rationed intermittently during the day. Solar cardboard box cookers are also easy to make, but they do require several hours of direct sunlight to cook with. There isn’t room to describe solar box cooking here, but excellent information and designs can be found online at: www.accessone.com/~sbcn Start saving cardboard rolls and have the children prestuff them with twigs, sticks and paper so you have a ready, and easy to use fuel supply. Barbara and I both have a spark striker (about $1.20) and cotton, plus matches, and old metal utensils for poking the fire, and protecting fingers. Place a wire handle on your rocket stove. Punch two small holes on with side of the can and add a wire handle for easy transport Practice making hot water, cooking instant soup or rice and get comfortable with the rocket stove. Knowing you can prepare hot meals and ensure safe drinking water gives you confidence that you can care for your family under any emergency or adverse condition.

“Build a Rocket Stove Cooker “is available by mail for $5.00 +$1.00 postage. * A Solar Wall Oven is patented design for a permanent solar oven built into the south side of a home or wall structure. It can also be used as a freestanding unit for mobile cooking.

Simmering rice in covered pot. Large stick used for feeding fire. Clay stove stands nearby. Frying an egg on the rocket stove. Top down view of 90º elbow, with partial foil insulation.

Additional information: Barbara is also a founding member of Solar Cookers International, a non-profit organization in Sacramento California. The goal of SCI is to help people, especially in poor, Third World areas, to cook without burning precious fuels. SCI and Aprovecho research and experiment with low-cost, low-fuel designs to develop both solar and fuel efficient stoves. However, tools like rocket stove, earth ovens, and solar cookers are practical for anyone wanting to conserve on fuel, and for possible Y2K, or off the grid cooking needs. To purchase the WAPI device send $6.00 , to Solar Cookers International,1919 21st St. #101, Sacramento CA 95814 USA, Tel: 916-455-4499, email [email protected]