Rocket Stove Adventures, Part 1: The Quickie!

The rocket stove in progress, soon to be a true rocket stove. 

My favorite way to cook is with a wood burning rocket stove.  Nothing compares to the taste of food cooked over natural wood, its nearly addicting.  In his research in off the grid living, John had come across the concept for rocket stoves as a solution for efficient wood burning cooking stoves years before he actually set out to build one for me to use.  When we lived in Cleveland and depended on a wood stove to cook our meals, he started looking into building a rocket stove for us.  The weather was getting warmer and it was too hot to run the wood stove inside, even just for cooking meals.  So he watched some youtube videos, made a plan, acquired materials and built it.  I was really pleasantly surprised by the results and we've been using them on and off since.

Rocket stoves get their name from the noise they make when they are built properly, whooshing and roaring so that they sound like a rocket.  They are very easy to build and improvise, just so long as you understand the basic concepts that make them work.  The end goal is to produce a wood burning stove that is both efficient and effective while producing less smoke and ash.

To do this, you need proper proportions of the heat riser to the burn chamber, as outlined in the drawing above.  You want the diameter of your feed chamber to be 1.5-2 times as wide as the diameter of the chimney.  This is so you can stuff half the feed chamber with wood, the section above the grate.  The bottom section is for air flow, this large volume of air is one of the keys to a effective rocket stove.  You will not achieve proper draw without this.  You also need the heat riser, or the chimney to be at least twice the length of the length of the feed chamber.  This allows the heat riser to function properly, acting as a strong vaccum once heated to draw air in through the air passage through the bottom to help fuel the fire, which spits out the top of the thing. How hot it burns depends on how quickly you feed the stove, as well as how much you fill it with to begin with.  

  You need to have a grate, or something to split the feed chamber for the wood to sit on.  The grate crates an air channel below the feed chamber. The air travels under the wood, through the burning wood at the back of the stove and up the heat riser, to heat your pan.  A rocket stove without this feature is not a rocket stove at all, just a more efficient wood burning cooking stove. Without these proper proportions and the use of the grate, your stove will never burn quite perfectly, you'll always have more coal and smoke left than you should.  In the end you'll end up using more wood too.  Once you see how a true, well functioning rocket stove works, all of this makes more sense. 

When we lived in Detroit, we told some friends how to make one themselves, as they expressed a desire to stop cooking using propane, as they were until that point.  They changed the proportions and got rid of the grate, and ended up with a completely different (and honestly crappy) wood stove.  It burnt 3-5 times the amount of wood, made a huge amount of smoke and left a huge pile of unburnt, wasted coals at the end of using it. This was an upgrade to them because they weren't using propane, but it could have been much better than it was.

As I mentioned before, my first experience using one of these was in Cleveland.  As soon as we got it functioning correctly, I was absolutely floored at how well it worked.  I was spending a quarter of the amount of time getting firewood ready, as you only need a large bundle for a large meal if you're stove is built correctly. It produced very little ash, and once we had it dialed in it was really easy to use.  So long as I had something to burn in it, I had a means to cook my food.  You can use what you have on hand for fuel by the way, just so long as it's not full of toxins that you'll be breathing (and eating) when you use the stove.  I've used cardboard and pine cones in a pinch, which work great. 

Within a few weeks of moving to Detroit, we had built another one out of local bricks salvaged from a burnt down house.  The photos above are of that stove, which we actually had with us when we were arrested (we left the giant slab in Detroit, too heavy to lug around haha).  Imagine the surprise of the police officers as they took 24 firebricks with soot on them out of my car and a little square of burnt up fence.  They had no idea what to think. We got the proportions correct after some experimentation and used a piece of fence we found nearby for the grate.  The stove worked like a charm and was really easily transportable, which is another advantage to these stoves. You can build them to be easily transportable, if you'd like.

There are so many different options for materials to build rocket stoves.  Our first one was made out of concrete bricks, which we stacked and arranged (with a metal grate of course) and surrounded with dirt once the stove was build.  Concrete bricks often have air bubbles in them, which can expand and cause the brick to explode when heated.  For this reason, we buried the outside of our first one to be sure there would be no catastrophic accidents.  We never had an issue with explosion. 

Our second stove was built using those recycled firebricks we found in Detroit.  This time, we went to our local building materials shop and ordered 80 of their red bricks, which cost us 240 pesos or around 12 dollars.  We didn't need nearly all of them for the stove, we will have a good number left over even after we rebuild the stove to use on our wood fired oven project. 

There are plans online for how to make your own out of concrete, using plastic buckets and pvc piping as a mold. I saw a plan today for one built out of rocks, cob and chicken wire.  Anything you can get together that you can build a leak proof J tube (fancy term for the combination of the burn chamber and chimney, shown in the drawing above) with will do the job.  Google rocket stove ideas for some interesting ideas ranging from using a miniature version made out of a soup can for making tea, to more permanent brick and mortar options.

For a true rocket stove, you'll need a grate of some sort.  A metal grill works great, anything strong that wont break down super quickly from heat, that'll still let enough air into the stove will work.  We've used all sorts of things, pieces of metal fence, the side of a shopping cart, anything you can find around that'll serve the purpose really. This is a crucial component, without it you've just got a wood stove. The use of the grate allows for proper draft, which makes this stove rocket. For the one we built yesterday, we used the side of a shopping cart, and it worked great with the clay slip mortar John made to fill the gaps. 

Choosing where to put a rocket stove is important.  We almost always start ours in a temporary spot with the intention of moving it later (as we're generally in a pinch, hungry and needing a place to cook pronto), and this rocket stove was no exception.  The photo above is the area John chose to put the stove for now, under one of the front corners of our house where there was already a decent amount of dirt dug out.  If you have the ability to have it covered without burning anything down (a roof several feet above the top of the stove is more than enough, realistically, we had one on our covered wood porch in Cleveland), go for it.  It makes cooking in the rain a much more enjoyable experience. I'm lucky because my house is made of concrete and metal, so having my rocket stove under my house is no problem. 

Prepare the spot where you intend to put the stove by flattening the ground at the very least.  The one I had on the porch in cleveland, we built a stone and log table for to raise it off the ground, making it a bit easier to access.  If you do something like this, make sure you use a non-flammable base to it the stove itself, preferably a large stone or something to that effect. A stone sitting on logs like ours was fine, as the logs were a decent distance from the fire.  

In our experience, a stone base is best for the stove, even if it's just an area of bricks.  In Detroit, we managed to find a huge stone slab that we used, which I loved for this purpose. We made one this time with bricks, as shown in the photo.  Next, lay out the first real layer of bricks, leaving a space in the center like shown for the burn chamber.  

With the dimensions of our bricks, we had to use two layers of bricks before the grate layer.  In our other stoves we've made, we've only used one layer of bricks.  How many you need to use depends on the dimensions of your bricks.  So long as your end result has proportions like the one depicted in the drawing above, your rocket stove should function correctly.  Just pay attention when building this part. 

The best way to handle the grate layer is add some homemade mortar using local materials.  Use clay heavy soil and some water to make a clay slip like the stuff shown in the bucket above.  Apply a layer to the bricks and put on the grate and press.  Add a little more slip to level things out and put on the next layer, or two if you need to.  

How you build the rest of the stove us up to you to decide.  This will depend on your materials available, realistically.  If you're using bricks, play around with the layout until you have a pattern that has the dimension ratios you're looking for to make it work.  If you have those ratios right, the stove should work fine from the first fire.

Above is the top of our current two burner system that we have set up.  Our rocket stove isn't exactly right because our ratios are not correct.  For this reason, the stove uses more wood than it should and doesn't burn nearly as efficiently.  Where there should only be a small amount of white ash, there is dark grey ash with some coals.  This stove is way more efficient than most of the wood stoves I've seen Mexican's using here, but it's not a true rocket stove.  

Once it's built, lighting it should be easy if its built correctly.  Stock the top half of the feed chamber with different sized sticks.  Leave a small amount of space between the sticks and the back of the chimney, so you prevent any issues with air draw. I stuff the bottom with cardboard or paper and light.  

You might need to give it a puff of air to get it really going, but realistically, once you light it it should go.  Just give it enough time to get started and you should have a roaring fire like the one above.  The stove is ready once the sticks are lit and flames are coming out the top of the thing.  You should also hear a slight roaring like a rocket here.  

Our plans are to redesign the stove a little and change it's location slightly.  John wants to put it a few inches further back, and possibly a few inches lower. There's a sloping pile of dirt in front of the thing because he threw it together in a hurry.  Last night, we essentially re-opened our hilltop restaurant, with the added draw being we would be using wood burning stoves.  While we had acquired the materials, we ended up putting off the construction until way late in the day.  John was just finishing putting the stove together, in the dark, when it was getting to be time for him to pick up our guests.  He did it in like 20 minutes, and honestly did a good job despite the circumstances.  It's functional as is, we'd just like it to be more efficient, a true rocket stove. 

He helped me light the stove, and went down the hill to acquire our friends for dinner.  I worked on tending the stove, quickly realizing that I asked John to start the stove too early.  I wasn't ready to cook and as a result I ended up running all over the property trying to get sticks and ingredients, all while trying to keep the fire going.  Needless to say, I handled it incorrectly.  By the time John came back up the hill, the fires were essentially out and I had barely begun the cooking process.  I was also running out of wood.  Off John ran to our carpintero neighbor, to ask for some scrap pieces of wood to burn to make the difference.

He returned with an arm full of wood and our hatchet and split it all up for me.  We got the fire going once again, and it kept going from then on out as I no longer had ingredients or wood to acquire.  The potatoes in water started to boil and I got some chicken tenders frying in my cast iron skillet on the other burner.  Things came together and dinner was delicious, despite being a bit late due to my lack of preparedness. 

All in all, despite not being a perfect rocket stove design, it was much better than some of the wood stoves I've used over the years.  It's still pretty adjustable and certainly got the job done.  There's a tiny bit more smoke than we'd like and there's coals in the ashes when there shouldn't be, but it's a work in progress, as are many good things in life.  We'll rebuild the stove to proper rocket form and share it once we do.  After that, we're on to the wood fired pizza oven, something I've been wanting to build for years.