We Built a Rocket Stove!

I got my birthday present over the weekend: two full days of my husband's help with a project on my (endless) list. It could have been cold frames, rabbit tractors, or the rocket stove; I didn't care which one we picked to get done. But I'm absolutely thrilled with the results of our labor.

Rocket stoves are an example of appropriate technology. They are exceptionally efficient wood-burning stoves that can be made from simple materials by people without any specialized skills or knowledge. Believe me when I say that our rocket stove perfectly demonstrates those last two principles. We have zero prior experience at bricklaying, and almost all of the materials that went into the construction of our rocket stove were either literally lying around our property, or were scavenged elsewhere. Based on the inspiration from Homegrown Evolution, I had in mind a permanent rocket stove made of brick. It's also possible to build portable ones in largish metal cans, as shown in this video. (Warning: gratuitous techno-pop background music.)


Despite giving the project our more or less undivided attention, it took two full days of work. First my husband, an engineer, needed time to digest the concept of the rocket stove. I'm much more likely to just run with a half baked idea and assume I can intuit how things should be done, so there's always friction when we collaborate on projects like this one. The rest of day 1 was taken up by prep work. First I cleared a space for the stove in what is eventually going to be our all-perennial area. Right now it's mostly a weed patch. Then my husband dug a hole deep and large enough to take this concrete block base, which (I swear I'm not making this up) we found while clearing away a debris pile in the back corner of our property. We carefully filled the hole partway with gravel (again, I swear, there was a pile leftover from paving the driveway behind our fence) and sand (we had a couple partial bags from other projects). Next we leveled the block and filled the central hole with more sand.

Shown are most of the materials which went into the construction of our rocket stove. Everything seen here was scavenged, but the stove pipe shown is 6" in diameter, so we needed to buy a 4" length.

Then we gathered bricks from around our property. Some were really old, dug out of the ground when we tilled for the garden, and some newer ones were left over from the previous owner putting in a nice walkway. My husband made a run to the hardware store for the few things we needed to purchase: more sand for the mortar mix and a length of 4" stovepipe. Believe it or not, we had actually scavenged a 4" stovepipe elbow joint during one of our dumpster diving runs last year, so we didn't need to buy that. Meanwhile, I cut up the steel can needed to fit inside the burn chamber, and cleaned off a scuzzy old round grill that we'd salvaged somewhere once upon a time.

Sorry for the blurry picture; it was getting dark. This is the unmortared prototype being fired up. You can see that some of the bricks have moss on them.

Then we built a prototype on the driveway, with no mortar between the bricks, and fired it up just to see how it would work. That went fairly easily and it taught us one valuable thing: we didn't want the fuel opening too close to the ground. Rocket stoves burn very, very hot, but our prototype at least needed a bit of blowing to get the flames going well. Bending down that low to the ground to blow into the burn chamber was no fun. We decided to move the burn chamber higher. We were deeply impressed by the amount of heat generated by a very meager quantity of green twigs, even without the insulation of the wood ash around the stovepipe. We were able to simmer a pan full of water over the flames, without a lid on the pan. That was the end of day 1.


Day 2 began with my unwelcome realization that we really ought to clean off the bricks we'd gathered for the project. Many of them were filthy and pitted. Some had moss growing on them. Obviously, not great material for sticking together with mortar. (Sigh. The costs of recycling materials rather than buying new.) Cleaning the bricks took up a good portion of the morning, and made us absolutely filthy.


After lunch, it was time to mix up the mortar and start laying. Like I said, neither of us had ever laid brick before, so we went to the internet for some fundamentals. But really, we had no clue. We did however have tools. Despite the small number of bricks in this project (just 48), it was hard work laying the courses, which we took turns at. I have a new-found respect for the skill and the sheer physical work of brickmasons. Our backs were killing us when it was done. I was fairly proud that we at least managed to finish with a reasonably level course of bricks, but the appearance of our rocket stove would charitably be called rustic. We covered the rocket stove with a sheet of plastic and retired for the evening.

This past winter I had thought to ask one of my relatives with a woodstove for a bucket full of ashes, in order to have them on hand whenever we got to this project. Thus I had one 5-gallon bucket of wood ash in the garage. Being non-combustible, light, and airy, ash serves as excellent, cheap, and widely available insulation around the stovepipe inside a rocket stove, concentrating the heat even more. We still need to add a few more inches of ash around the stovepipe chimney, and then cut a piece of sheet metal to fit around the chimney and cover the ash. Other than that, the construction is done.


After the mortar set up for two days, I decided to test out the cooking possibilities with an egg for dinner. It wasn't very elaborate, and I had to bring the toast from the kitchen. But our own homegrown egg cooked up beautifully with some greenery snipped right from the garden. Hardly any ash on my inaugural rocket stove meal!


I'm absolutely thrilled with my birthday present, especially because we built it ourselves at almost no expense. As soon as it was constructed, I started looking at the ground around it, and wondering which perennial culinary herbs it would be best to plant nearby. I'll divide my chives next spring and plant them within easy reach, and I think I'll put some lemon thyme in not too far away. I had asked that the rocket stove be situated just near the covered area next to our shed. So we have a convenient place to accumulate a pile of twigs and keep them dry. With some work we could pretty up this area and make it a nice place to hang out and contemplate the garden. More tasks for the list!

All the fuel needed to cook my egg dinner.

The rocket stove is so hot that I don't envision using it for grilling, even though it's topped by a grill, but perhaps we'll eventually get the hang of producing a low flame. It will easily boil a pot of water, and I'm sure we will learn the ins and outs of cooking over heat so intense. I see the rocket stove as a way of efficiently using the huge quantity of deadwood that drops from our six remaining full sized deciduous trees each year. It will be an emergency backup for cooking in any weather. If we lost power for a long while during really cold weather, we could at least heat water to keep ourselves warm with tea, soup, and hot water bottles.

So...I'm in the market for one-skillet recipes!