How to Make a Rocket Stove
As a frugal and self, sufficient individual, you may be interested in an alternative to the earthen block, tin can or commercially made, version of a rocket stove. Here is another effective alternative to those found in articles that are circulating on the internet, YouTube or in “Prepper Blogs” these days.
I have not seen anyone touting or describing how to turn common black stove-pipe fittings into a rocket stove so I will try to explain the process I use to make a rocket stove out of common stove-pipe fittings. This version is possibly one of the best compromise devices for cooking over wood in a grid down or where firewood is of limited supply.
When firing up this little stove, I typically use cut up and split SYP scraps from my home repair business, which I set aside for just this use. I find that utilizing this design for a rocket stove it only takes about 3 or less, one foot sections of 2×4 split down into ¼ or ½ inch thick kindling to boil water in as little as 5 mins, if you have the wood pre-split and readily available, along with your utensils, pans, and foodstuffs close at hand.
With this very fuel-efficient, design, there is very little smoke exiting from the stove, and little or no ash to contend with. Other than the usual soot associated with using SYP (southern yellow pine) wood due to the high resin content of the wood there are few drawbacks to this stove.
f using tree limbs gathered from the forest floor, this soot may not be as much a problem in a conifer filled area. I carry my stove in an old canvas, firewood tote, so as not to get much of the associated soot on my person but this may or may not be suitable for you.
Some of the advantages of the rocket stove designs out there are the speed and efficiency they offer and this design is not different. If you are familiar with hand tools, and your local hardware stores you should have little or no problem making one of these little stoves in as little as 4 hours or less not including time to gather your materials.
The tools I recommend for making this small stove are as follows: Philips head screwdriver/cordless drill, 1/8 dia. And ¼ inch Drill bits, two dozen or so 1-1/2 to 1-1/4 inch long drywall screws, or deck screws, a set of good tin snips (I like the 2 inch long-bladed, RH version).
The drill you use should have at least 2 speeds, high and low. I believe using the higher speed to drill metal works best. I also recommend leather, work gloves, safety goggles, pencil or sharpie a tape measure and a free afternoon to purchase the materials and assemble the stove.
Below I have listed the materials I recommend as well as some price points of the materials found at my local “ big box” store, for the major items you will need, these prices are only for comparison purposes and may vary as this article ages, your place of purchase will probably be different. The prices I found are included next to the Item description as of December 2015.
One black pipe cleanout, T fitting, 6-inch dia. (may also use 8-inch dia. T as a substitute just make sure you buy corresponding fittings) $15.00. This fitting will become the main body of the stove.
Two each cleanout caps/end caps, 6-inch dia. $6.00 each. One will become the base/clean out at the bottom and the upper cap will become the burner plate/diffuser at the top of the stove. When orienting the stove one end will be smooth, and one end will be crimped to accept the pressure fit, end caps. Please note the two different orientations of couplings so when you buy them, you wind need to line them up with the correct configuration.
One 4 inch vent pipe, elbow, 26 gage or heavier, $3.50 ea. (I could not find 4-inch single wall black pipe, elbow fitting so I was forced to use a galvanized pipe).
The next Item you will need to purchase is a 4-inch window thimble made of 24 gage aluminum or if you cannot find a window thimble use surplus sheet metal left over from the 2 ft. section of vent pipe listed below. I chose to go the route of using a window thimble as I had one on hand from another project.
A blank piece of galvanizing can be used if a thimble is not available. I do not have the price of the thimble since I had it on hand.
The next item you will need to assemble your stove is a 2 ft. section of 4-inch dia. stove-pipe or 26 gage, galvanized vent pipe $4.00 each.
Next up for those who want to use a stainless steel “hose clamp” please find a clamp that will accommodate the dia. of the pipe you have assembled using the appropriate size of your legs coming off of the clean-out T, (mine was made of a 6-inch dia. coupling). I Opted out of using a stainless clamp and used some aluminum strapping I had lying around but the clamp would work just as well or better than my arrangement.
It might also be handy to have on hand ½ dozen or so, ¼ x ½ inch sheet metal screws with the slotted hex heads for easy driving.
The last item you will need is hardware mesh or wire. The wire I used was 18 gage with ½ inch grid but you may find wire with larger or smaller mesh. The fire-grate will be constructed from this material and the heavier gage, the better, as long as the mesh size remains smaller than 1 inch or so in order to retain the coals better in the small firebox.
The total cost of the materials of the stove should be around $40.00 to $50.00 not counting your labor, which I believe makes this a very affordable and portable addition to your arsenal of grid down appliances.
This completes the list of Items you will need unless you chose to insulate the 4-inch interior, lining of the stove to keep the outside body of the stove from getting too hot. I chose to forgo the use of vermiculite or insulation since I wanted my stove to cool off quickly and give off radiant heat while it operates. I could not tell if the stove would use less fuel by being insulated but some swear by it so let your stove be built as you please and publish and findings you have supporting insulation if you like.
A word of caution here, do not operate any open flame stoves such as the one described in this article, inside the home unless this item is vented through an approved fireplace or wood burning stove-pipe properly constructed and designed to prevent smoke/C02 buildup in your home.
In addition, when using galvanized pipes/materials as a substitute for black stove-pipe realize that burning galvanized pipe will give off harmful fumes until the galvanizing has turned white and started to rust.
This curing of the galvanized parts must be done prior to cooking or using of the stove to make meals over and should be done in a well-ventilated location such as an open fire pit or wood burning stove. Once the galvanizing is burned or cured, normal use can be observed). If you have a source of 4-inch black stove pipe you can eliminate this step, but again I was not able to find 4 inch, black, stove-pipe in my area.
Now onto the fun part, the assembly of the rocket stove. This assembly is pretty straight forward and if I leave out any details you should be able to figure out the assembly from the pictures provided.
First I took a pair of tin snips like the one listed above and cut a section of the 26 gage vent pipe/stove pipe about 10 to 12 inches long. This was then assembled to the normal configuration so the sheet with snap fold becomes a pipe again (easier to cut the sheet when it is uncoupled). The section of short pipe can be set aside for now.
Next take the 4-inch vent pipe, 26 gage elbow, and configure the fitting so it represents a 90-degree elbow. This may take some manipulation but the design of the modern vent elbows makes life so much easier for those of us who do home improvement projects, and in fact, it is very hard to find a true 90-degree elbow should you try to find one in the galvanized and aluminum duct or vent pipe. A word of caution, do not substitute aluminum pipe for steel or galvanized pipe here as the aluminum pipe is very thin gage and will melt through after a few uses, (I found out the hard way).
Now place the 4 inch elbow inside of the larger (body of the stove), cleanout T fitting, with the top of the elbow fitting in the top of the stove body (will fit down inside 1.5 inches from the top of the stove body) and the elbow portion sticking into the horizontal section of the stove T. This smaller coupling will sort-of “slop around” in the bigger fitting for now but do not be concerned as we will address that issue shortly.
Now slide the 10 inch or so section of 4-inch pipe in the lower leg of the 4-inch elbow, at the horizontal leg of the stove body. This will become the combustion chamber, once you get the stove assembled. This will fit but your 4-inch elbow pipe should be able to be centered in the top leg and side leg with the 4-inch elbow touching the interior of the stove body at the inside corner of the curve. Things will be secured later but for now just test fit and set aside.
The next step is to cut notches in one of your 6-inch caps (this will be your top burner plate/flame diffuser). The cap, notches should be equally spaced around run of the pipe, mine are about 1.5 inches long by about 1.5 inches deep, and I made about 4 of them.
These notches do not extend all the way up to the flat part of the cap and are deliberately designed this way but if you choose to or did so by accident do not be alarmed things will work just fine this way also.
These notches will act as air vents and smoke exhaust ports. You will notice that the 4-inch coupling does not come all the way to the top of the stove body, but this is to allow for the flames to form and breathe
Now get your drill and drill bit and drill 1/8 inch holes in the top of the stove body. These holes need to be about 1.5 inches down from the top edge of the T-pipe. I chose to make the top of my stove the smooth edge as my end cap compatibility was so oriented, as opposed to the crimped edge but this is not critical just so long as the lid/cap will fit inside or outside of your main stove body/Cleanout. Now you can choose to drill a mirror image of these holes for the bottom edge of the T-Pipe but I chose to just push my bottom cap in place with the good pressure fit the smooth/crimped edge of the pipes come supplied with from the factory. I chose to use a galvanized, 6 inch cap for the bottom as there is little or no heat buildup at the base other than a few coals finding their way to this location, and If I recall, I was not able to find the male crimp end made of black stove pipe when I assembled my stove a few years ago.
Now comes part where you center the smaller pipe and the larger pipe so the stove functions as a rocket stove and the walls will allow for convective air flow if you want to have radiant heat.
I drilled holes on the upper T-leg about 4 inches of the way down from the top at 4 locations symmetrically around the diameter. Then using 1- ¼ inch drywall screws as set screws to hold the inner elbow in place. I then repeated the process for the Horizontal firebox section of the 4” pipe and tried to run the screws just as a press fit and tried not to penetrate the exterior of the inter-pipe.
This did leave a small portion of the drywall screws proud of the 6 inch, T’s, outer wall but did a great job of holding the inner pipe and elbow in place using the 8 screws as jamb screws. The pictures of the interior of the stove should make this pretty clear.
Next, I fabricated the thimble wall of the horizontal leg cover of the stove where the fire-box leg comes out of the larger leg of the 6” clean out pipe/main body of the stove. In order to do this I held the 4-inch window thimble at the bottom of the stove and made a trace of the diameter onto the window panel.
The 4-inch diameter Thimble hole will be situated at the lower portion of the firebox so it should be positioned as such. What this will look like properly positioned, will allow for dove tail fingers to be cut in the panel that sticks out past the traced line.
This will become a 6-inch circle, inside the center of an 8-inch circle, with the 4-inch thimble hole located at the lower center of the fabrication. The 4-inch thimble, hole will be positioned so it rests near the bottom of the 6 inch horizontal opening of the body of the pipe, with the flat surface covering the remainder of the horizontal, 6-inch hole. This sounds a bit complicated, but please look at the photos accompanying this article for clarification.
Now it is time to cut the 2-inch dovetail fingers into the sheet of aluminum or steel of the remaining metal outside of the 6-inch hole. Dovetail fingers can be cut at straight or tapered cuts but should be spaced about ¾ to 1-inch intervals.
I found that tapered cuts work better for me but your results may vary. There is a bit of art to cutting fingers but I came up with about 24 fingers (48 tapered cuts), using tin snips to make them. I did not remove the alternative fingers but bent every other finger in, in order to fit inside of the 6 inch vertical leg of the stove body. The remaining 12, alternative fingers fit outside of the body of the stove.
I then used my aluminum straps (or stainless hose clamp) and sheet metal screws to fit and hold the window thimble in place so the hole of the thimble helps hold the firebox of the stove in place.
Alternative methods can be used to make this cover up the horizontal hole, up to and including using a hole in a flattened piece of tin made out of any type of sheet metal as long as it will be large enough to make the cover accommodate the dovetails and hold the firebox in position.
Four to six sheet metal screws can also be used to hold this cover in place or in conjunction with the straps or pipe clamp.
The only thing that remains to be fabricated in order to fire up the stove is a fire grate. I chose to use the hardware mesh mention in the materials list above. I cut a section of mesh long enough to fit from the outside edge of the 4 inch, horizontal, firebox to the back of the body of the stove so my mesh was about 14 inches long.
The mesh was cut wide enough to make a role of wire mesh just big enough to just fit snugly inside the 4-inch diameter of the firebox. The mesh can be a little short but should not fit outside of the 4 x 6-inch firebox section, fitting outside of the main body of the stove.
The pictures I took do not have the hardware mesh fitting in the firebox but what I found works best is to collapse one half of the diameter of the mesh so that it just comes within about ¼ inch of the opposite side of the mesh roll, with the large divert of the mesh on top of the basket or coals catcher (looks like a crescent moon laying on its back when it fits inside the 4 inch firebox).
This arrangement provides maximum, retention of the coals and draft of the air in the combustion chamber.
The next step is the decision to make this an insulated or radiant stove. I opted to make the stove with the ability to radiate heat so I drilled about a dozen ¼ inch dia. holes 2 inches from the base of the stove body. These are for convection and do not enhance the stoves oxygen intake as far as I can tell. These may not even be necessary and if you are a mechanical engineer, you can tell if they are even needed.
On the second version of the stove I made for a friend of mine who fell in love with mine, I made some legs out of the remainder of the 4 inch galvanized pipe that was triangular in shape, made of three folds of metal bent into a one inch wide strap with the bottom of the triangle resting at the base and the back tabs screwed into the wall of the 6 inch body of the stove.
These were made of 12-inch strips cut 3 inches wide with a 6-inch base but if you use small, light, weight pans to cook with these should not be necessary.
I hope you found this article to be informative and give you and your alternatives if the grid should ever go down and your source of wood to burn is scarce.