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bennelson 07-21-10 11:52 PM

Building the ROCKET STOVE
Hi everyone.

In case you've never heard of a rocket stove, it's a simple style of a stove, with a feeder pipe and a vertical chimney, which makes efficient use of fuel by giving it plenty of air.

The rocket stove "self-drafts": the feeder tube is split in half, with the air coming in BELOW the fuel (typically wooden sticks).

This rocket stove is made from metal - in this case reusing an old household water pressure tank (you may recognize it from my solar water experiments...) and some thin-wall steel pipe of about 6" in diameter.

The whole stove should be about 30-33" tall when done, so that it's a good height to use while standing.

Besides using the rocket stove as a replacement for an LP grill, I also want to be able to bake in it. I brought out my cast iron dutch oven to make sure it would fit inside the tank used for the top part of the stove.

I used an angle grinder with cut-off blade to cut off the bottom of the water tank tall enough for the cast iron to fit inside. I had already cut off the TOP of the tank for a previous project.

The tank is a 16" diameter - plenty big for a grill, boiling a stock pot, or baking in the dutch oven.

The first step was to cut two pieces of pipe for the project. I only had to cut one, as I found a scrap piece close enough to the right size in the first place.

The two pieces are:
1) The vertical "chimney" piece
2) The fuel/air feeder tube

Since the feeder tube goes into the chimney tube at an irregular angle, it's a bit of a trick to lay out the cuts. A friend of mine (Greg) already made a steel rocket stove, and designed a tin template to mark the pipes.
When done, the feeder tube looks pointy. Don't trip and land on it. The tin template is in the background.

For a base for the stove, Greg had some old farm implement discs around.

The chimney pipe needs an odd-shaped hole to accept the feeder tube. Here's the template in front of the pipe. The template gets wrapped around, and I mark the hole with a Sharpie.
The two cut tubes, designed to fit into each other. I used a flapper disc on the angle grinder to clean up the sharp edges of the cuts, as wells as to prep the metal joints for welding.

After test-fitting the two parts together, I looked for the high spots to trim down a little, and used a file on the inside corner as well.

Here, Greg gives me pointers on making everything line up and be nice and clean.

The feeder tube was too long, but I figured I could always chop it down later. Here, I wrapped sheet metal around the tube to make a nice right angle I could mark and then cut the tube short.

Then, I set the chimney tube on top of the upside down tank section, and marked where the tube goes. Not sure what's the best way to cut a perfect circle like that in steel. (The tube is an odd-diameter, so that rules out hole-saws!)

I might also be able to reuse the plug from the tank as an ash clean-out.
I also zinged off the base ring of the tank, as it's not needed - the tank no longer sits directly on the ground. I though it looked nicer without that ring, and it won't be in the way for welding.

I've got one afternoon's worth of work into the project so far. Out of pocket costs are nil. I now have a base, chimney and feeder tubes, tank section, and the tank top, which will become a lid.

Still to do is welding all components together. That should be interesting, as my welding experience is rather limited. Also, I will need to fill in the square hole in the middle of the base, and add an ash cleanout to the bottom of the chimney pipe, directly opposite the feeder tube. I still need to design the grate that separates the fuel from the air intake in the feeder tube.

Once those things are done, the simple Rocket Stove is completed. However, the sky is the limit to add to the stove. Here are a few photos of what Greg has done with his.
While I was working on my basic rocket stove, Greg and friends were polishing the steel top of his grill. The custom grill allows the combustion gases to flow THROUGH the grill and out the vent on the left. He was also working on designing a warming tray that would then mount to that. On the right, a simple oak board had its corners rounded off, sanded, and then hand-rubbed down with mineral oil to make a GORGEOUS sideboard.

Hope mine comes anywhere CLOSE to looking that good when it's done!

Daox 07-22-10 07:10 AM

Cool stuff Ben. I remember you posting a pic of a lot of smaller scraps of wood and sticks. That is perfect fuel for a rocket stove.

bennelson 07-25-10 09:03 PM

Yep, I have lots of LITTLE pieces of wood around for fuel....

Yesterday, I got to do the assembly and welding of the stove.

I have very little experience welding, but a friend has a wire-feed welder and those sure seem easy to use!

I welded the main pipe to the base and then the feeder tube into the main tube.

The angle of the feeder tube made that weld a little trickier, but it was still pretty straight-forward.

Then I set the whole thing upside down and marked the cut-out for the section of the old water pressure tank. I traced the main pipe with a marker, and then cut just inside that line with a plasma cutter. (The other reason why I stopped at Tom's was for THAT special tool!)

Here, you can see that basic finished unit.

I still needed the divider that separates the air from the fuel down the middle of the feeder tube. I found some scrap metal that already had some slots in it (for air) so I cut that to the 6" width to fit in the feeder tube.

You can see how that plate goes right down the middle of the feeder tube, cutting it in half the long way.

Here's a top view of the divider plate. As you can see, the end will need to be rounded to make it fit all the way into the upright pipe.

And FINALLY, actually using it!

I don't have a cooking grate yet for it, but I already had a grill for camping around, so I just laid that over the top! Later, I plan to have a custom grate for it. If I get really lucky, I might be able to find something in stainless steel from a scrap yard.

I also need to weld in brackets to hold the grate and some lower brackets to hold either a stock pot or dutch oven.

The other thing I would really like is a sideboard/cutting board. Since the water tank had threaded ports on the side, I might just be able to reuse one of those to connect in some gas pipe which would hold up the table.

Daox 07-26-10 07:52 AM

How did it work?

bennelson 07-26-10 09:35 AM

Works great, I have the singed arm hairs to prove it.

I still need to modify the divider grate so that it lets in plenty of air, but doesn't let little burned pieces of coal fall down through it. I think I'm losing some heat that way.

Having a working lid should help it cook more efficiently as well.

bennelson 11-07-10 10:26 PM

End of summer.

I just plain didn't end up doing much grilling out this summer.
When I did, it worked great.

The stove does make a pretty distinct hot spot in the middle though. I think some sort of a heat-spreader would work well.

Also, I want to take this grill with me camping! :thumbup:

Corn was especially fun on the grill.

bennelson 05-29-11 04:03 PM

Must be spring!

Time to fire up the grill. Corn was on sale at the grocery store for the Memorial Day weekend.

It has been raining all day. I set the grill on the ground, just off my covered back porch.

Part of the design of the rocket grill is that a stock pot sits right inside. I recently found a stainless steel stock pot at the thrift store for $4. This is the one that it won't matter if it gets left in the rain or covered with soot!

I usually use fry twigs or scrap wood in the rocket grill, but since it was raining, any of that would have been wet. Instead, I still had some cedar scraps from the winter firewood pile on the back porch, so cedar it was!

After lighting the stove, it took about 15 minutes to get a stock pot of cold water up to a rolling boil.

Then I threw the corn in. I kept the lid on the stock pot as well as the stove lid on top. At first, I was worried about rain running into the stove and killing the flame, but once the grill was hot enough, rain water just vaporized off the lid!

The stove also now has a lovely rust patina on it since last time you may have seen it.

In this photo, you can see how much of the stove is still under the eave of the roof.

Corn Boiling...

If you look to the left of the corn, that's all steam coming off it. This is several minutes after pulling the corn out of the water.

Corn seems to be the best/easiest thing to make on the stove. I still plan to eventually make a wok for it. The stove makes a high heat very fast - perfect for wok-style cooking.

I would also like to figure out what I would need to do to bake pizzas in it!

It's fun to be able to cook like this. Not that it displaces a TON of electricity or natural gas, but it is net carbon neutral! It's also good to know that if there was a long-term power outage, I would still have the ability to cook.

d3vi1d06 02-20-12 12:50 PM

Awesome. I came here to this site right after I discovered this rocket stove through youtube browsing. I was hoping I could share something new with the community, but the OP beat me to it, by 2 years lol.

Im not gonna steal your flame (Pun) but I would like to share a good site in reference to the Rocket Stove being used for other purposes.

Rocket Stove Design Base - Home

bennelson 02-20-12 01:02 PM

Yep, lots of good info at that site.

The cool thing about rocket stoves is that they can be as simple as 3 rocks with a pot on top of them, or as fancy as a big cob-covered set of steel drums that warms your whole house!

Xringer 02-20-12 07:01 PM

Three rocks?? Don't get corny on us Ben.. ;)

One of my fav pics on this site!!

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