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Tuesday, November 20, 2012

Building a DIY Rocket Stove

Original Article

8088229297 14e8bb782a o Building a DIY Rocket Stove   Backdoor SurvivalRocket Stoves are pretty neat.  Common among campers and backpacking enthusiasts, rocket stoves are relatively new to urban dwellers or those that do not spend a lot of time outdoors.  But wait – here come the preppers who seek fuel efficient ways to cook outdoors when the grid goes down.  Not to make light of the situation, five years ago I had no idea what a rocket stove was nor did I know how they worked.
How times have changed.
While there are many commercial rocket stoves (and I own two including the Solo Stove and the EcoZoom Versa) an efficient rocket stove can be had for as little as a couple of bucks as you are willing to do a bit of work.
8087990310 a4a7e5c039 n Building a DIY Rocket Stove   Backdoor SurvivalBut first, just what exactly is a rocket stove?
According to Wikipedia, a rocket stove is an efficient cooking stove using small diameter wood fuel which is burned in a simple high-temperature combustion chamber containing an insulated vertical chimney that ensures complete combustion prior to the flames reaching the cooking surface.
Seems simple enough, especially when you consider that rocket stoves are found more commonly in third world countries where wood fuel sources are scarce so an efficient system for converting twigs, branches, pinecones, leaves and other bits of biomass to fuel is essential to cooking.
Now as good as I am around the kitchen, in the garden and with the home and domestic arts, building stuff comes not so easy.  So I asked Backdoor Survival sponsor Ron Brown who is a retired engineer and really good at this stuff to help me out with some detailed instructions for building a DIY Rocket Stove.  He has convinced me that the process is easy and cheap, even for someone like me!
A Bit of Background
Ron told me that many years ago he made some maple syrup. Lacking any guidance, he constructed a boiling-down arrangement consisting of a simple campfire under a kettle. It takes 13 gallons of tree sap to make one gallon of syrup and he made several gallons. It was delicious but he burned a mind-boggling amount of firewood in the process.  Not at all efficient and not something you would want to do in a survival situation.
Improvised rocket stoves that are common around the world come in lots of designs and various configurations.  Their common advantage stems from a principle whereby three sides surround the fire while one side remains open. This facilitates combustion of the fuel and the ultimate creation of heat.  Of course, “real” rocket stoves are double-walled and have insulation between the walls.
What we will be describing here uses just a big, institutional-sized tin can with one wall.  Buy hey, it works.  And besides, 80% of the efficiency improvement over an open campfire (Ron’s estimate) comes from the basic three-sided feature while only 20% comes from the insulation.
The Almost Free DIY Rocket Stove
To get started, you are going to need the following:
1    No. 10 size steel can (institutional size) You can also use a 3-lb. coffee cans or a one-gallon paint can
1    cast iron trivet (check the Dollar Store for this)
1½ cups marbles, small rocks, or gravel
1    hinge
1   “turn button door catch”
2   bolts for door-legs (size 8/32 x 3) with 4 nuts
5   sheet metal screws for door hinge & door catch
Utility knife
Can opener
16-penny nail (sharpened) to serve as a punch
Short length of 2 x 4 (to clamp in vise and use as support when cutting/punching can)
1. Cut off the can’s top and save it. Empty the contents, rinse out the can, then cut a rectangular hole to make a door in the side of the can. The can shown here is 6″ in diameter and 7½” tall. The door is 5″ wide and 4½” high. The bottom edge of the door is 1½” above the bottom lip of the can.
To cut out the door, I support the underside of the metal with a stick of wood clamped in a vise and simply cut the sheet metal with a utility knife (the kind with the replaceable blade). Admittedly, this method takes a fair amount of strength and not everybody will be able to do it this way.
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An alternate method is to use a sharpened nail and punch a row of small holes along the perimeter of where you want the door to be. Punch the holes as closely together as possible. Then use a knife or a hacksaw blade to cut just the webbing between the holes. It’s a bit slow and tedious, but it works.
Tin snips are not practical for this job. Tin snips have jaws the width of your finger. We want a narrow slit plus four square corners.
2. Put one small hinge in the bottom-center of the door. Fasten it to the can with either small nuts-and-bolts or sheet metal screws.
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3. Install 2 bolts near the top of the door to serve as legs when the door is open. In use, the door stays open most of the time and serves as a mini-table to support the fuel-wood that we feed into the flame.
4. Install a small metal “turn button door catch” to hold the door closed when it’s not needed. As shown in the pictures, I fashioned a catch from “plumber’s strap.”
5. Punch a row of holes around the bottom of the can to let in air. Or, cut triangular holes using a church-key style can opener. These holes are down near the bottom lip of the can but are in its sidewalls, not in the can’s bottom.
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6. Put gravel or small stones or glass marbles in the bottom of the can. You’ll need about a cup and a half. (Marbles are best because natural stone contains moisture which can turn to steam and split a stone in half when it expands. POW! It doesn’t always happen but, if it does, it will get your attention, guaranteed.)
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7. Punch lots of holes in the upper can lid that we removed in step #1. Place it inside the can, on top of the marbles or gravel. The lid-punched-with-holes is then the floor upon which we build our fire.
Combustion air enters through the holes we punched in step #5, circulates between the marbles, comes up through the holes in the floor, and feeds the fire with oxygen.
8. Oh! Lest I forget. The Dollar Store trivet will come to you painted. That paint will bubble and scorch off in its first use. Scrape away whatever remains.
9. In use, put a flat stone or a layer of firebrick under this stove. Glowing bits of wood will leak out from time to time.
10. Think safety! This is a live, burning fire, nothing to joke around with. Leather gloves, pliers to use as tongs, a fire extinguisher or bucket of water . . . all excellent ideas.
Some Extra Credit Hints
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When used as a rocket-stove top, turn the trivet upside down if you’re cooking with a large pot or griddle. The legs on the trivet, pointing skywards, support the griddle. You can’t block off the top of the can (what amounts to a chimney) completely. There must be some space around the bottom of the pot or griddle for smoke to escape.
This stove can be used as a small charcoal grill. Despite its crude appearance and obvious limitations, it works well. Once started, it boils water faster than the gas range in the kitchen.
By the way, neither Ron nor I have discovered where the “rocket” part of the name comes from. Maybe it just sounds sexy. Perhaps far more relevant is the question, “What’s for dinner?”.
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The Final Word
Factory made rocket stoves are great but they will set you back about a hundred dollars on Amazon and elsewhere.  These are highly efficient and look “pretty”.  But as Ron says:
For my money, seeing as how we’re burning pine cones, twigs, and scrap lumber . . . and seeing as how this is for emergency use, not day-to-day cooking for life . . . and seeing as how the factory-made model is just as dirty to clean out as this one . . . and will carbon up the bottom of your pots and pans just as quickly . . . I’m gonna opt for the improvised/free version. Free is good.
Just keep in mind the following disclaimer:  Use this rocket stove outside. If you would not start a campfire in the middle of your kitchen countertop then don’t use this stove in the middle of your kitchen countertop. Don’t lay your bare hand on the trivet-top to see if it’s hot and ready to cook. Don’t pour gasoline on the flames to see what happens. Don’t toast firecrackers on the griddle. And do be careful of the raw edges on the sheet-metal door; they’ll cut you. This last bit is for real.
Enjoy your next adventure through common sense and thoughtful preparation!
PS – My sincere gratitude goes out to Ron for his help with this article and especially for the photos. His wit and sense of humor continually amaze me. Be sure to visit Ron’s website at Lanterns, Lamps & Candles.  His e-book on CD is also amazing!

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