Wednesday, June 3, 2009

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!

34 comments:

hickchick said...

My husband is not an engineer but we do the same things. I want to wing it he wants to measure and plan, arrrgh! This is a really cool idea. I think about what would happen if the power went out for an extended period of time and this would be a wonderful 'ace up your sleeve' ! Thanks Kris

PS i have more questions about your chicken tractor--how many sq feet per bird, commercial feed-how much? Please stop by my blog if you can...

Wendy said...

It seems like we have more in common than we knew. My engineer husband and I occasionally differ on how a project should progress. I like to jump in with a hammer and a half-hashed plan, and he likes to have a complete schematic :). Of course, most of his projects are still standing, and mine ... well, I've learned to mention something I'd like done and then let him figure out how it should happen ;).

I love the stove. We've been trying to figure out something for boiling down our maple sap, and this might be just the ticket. Thanks for sharing your project ... and happy birthday! ;)

Melinda said...

So cool! Wow. I'm sure it doesn't seem so to you, but I am surprised at how easy it is to make one. Awesome.

Wretha said...

Very cool! I love your design, it's very much how I picture mine to be when I build it. :)

Thanks for documenting this for all of us.

Wretha

Julie said...

Kate that's awesome! I'm getting a cheese press for my birthday but now I'm longing for a rocket stove LOL.

pelenaka said...

Congradulations on a job well done & thank you for the great pics especially the pic showing the foundation.
DH & I were discussing building a version of the rocket stove for outdoor canning to replace my cast iron laundry which is starting to show it's age after a 100 years.
Oh, perhaps the answer to being able to grill or sautee on a rocket stove would be trivets of various heights. That is what I use on my laundry stove.

Country Girl said...

Ha, my husband and I get along like that too. He is methodical I am helter skelter. I like to work with him because we get things done but it can be painful to work with him. Love the stove, would love to bulid one. I have one fireplace I can cook on now so that will have to do.

Homegrown Evolution said...

Wow, way cool! Looks like you've made some nice improvements on the design--and thanks for the link!

Michelle @ Find Your Balance said...

That's so cool! You could make pancakes. Or a cassoulet! So neat.

Kate said...

Hickchick, I definitely see it as an ace up my sleeve. But I'm also going to try pretty hard to make it something that we use regularly. About our chicken tractor/pen, it's 5'x6'. I wrote about the dimensions for it and our stocking rate in my earlier post:

http://livingthefrugallife.blogspot.com/2009/04/going-mobile-with-backyard-flock.html

You can leave me your email here (I'll delete your comment soon after) so we can communicate more easily if you have any further questions.

Wendy, I always feel a certain camaraderie with women married to engineers. My theory is that we're really not all that scattered, but that anyone looks that way compared to an engineer. If I could simply mention something I'd like done and leave him to it, I certainly would. But either my list is too long, or his time is too limited most often. I *have* to jump in and make a go of it, if my projects are to get done.

Melinda, yeah, on the balance, it was surprisingly easy. That's the virtue of appropriate technology. Would've gone a lot faster had we not needed to clean the bricks and if we'd had all the materials on hand before we began.

Thanks, Wretha. And good luck on your rocket stove when you get to it. I hope you'll document yours as well.

Julie, Happy birthday to you too. I could see longing for a cheese press someday too. It's just pretty far down my list of priorities right now. Homesteaders envy, perhaps?

Pelenaka, thanks. If you want to use a rocket stove for some sort of sustained heating, beyond say 10 minutes or so, you might want to experiment with stove pipes of different diameters in an unmortared prototype. The thing about the rocket stove is how hot it burns, but also how quickly it consumes tiny bits of wood. So you need to feed it fuel pretty steadily, at least in a 4" stovepipe. A 6" diameter pipe might need less feeding since you could use larger pieces of wood. Just keep the need to steadily feed in the wood in mind. You might not be able to wash and keep the fire fed all that well at the same time, at least not without help.

Country Girl, if I had a cook stove or any sort of indoor woodburning stove, I probably would never have wanted a rocket stove. Though the rocket stove is probably more efficient than almost any woodstove, I'd probably prefer something inside.

Homegrown Evolution, you're quite welcome. Thanks for stopping by, and thanks for the inspiration.

Michelle, good suggestions. Thanks!

Wendy said...

"But either my list is too long, or his time is too limited most often."

Same here. Mostly, I've become very patient - eventually, it will get done ;).

Anonymous said...

Cooking in a wok would be a natural fit with this stove - you need a short, hot fire for stir frying.

interesting blog btw, I just ran across it.
Jen

Kate said...

Wow! Jen, that's a great suggestion. I don't know why I didn't think of it. Now I'll have to keep an eye out for one of those dinky little woks that work not at all over a stovetop burner, while I'm out patrolling yard sales this year. Thanks!

eatclosetohome said...

This is *perfect*! I can cook a little bit on my fireplace insert, but there's no way I'm using that much fuel in the summer. This is a great solution, especially since we can't rely on the sun for solar cooking. Ok...I totally want to build one of these next summer!

Emily

Kate said...

Hey Emily, glad you like the idea. My plan is to actually use this to cook on more often next year. Not having dried kindling was a handicap this past year. But we have a large supply of small branches drying out now. So no more excuses. Be sure to post about your rocket stove, please, whenever you get it built.

Roger the Shrubber said...

Hi there, I found this account of the rocket stove so clear that I might just try it sometime. I'm working on the wife to convince her we need a "Kiko Denzer" earth oven and maybe this'd sit nicely next to it.

I'm learning also about permaculture through Toby Hemmenway's book and am building an apple tree guild this year. stop by my blog about Ecolife in Germany.

Kate said...

Hi Roger, thanks for letting me know you found the post useful. Gaia's Garden is an excellent introduction to the concepts within permaculture. I'm glad you're enjoying the book. Now I'll have to go look up the oven you mentioned. Eventually I'd like to have an outdoor bake oven for summer use. The ideal of course would be to integrate it with a detached sauna, so we could get clean and bake bread with the same fire.

Bobby said...

Great job. Looking to try and build one myself, but portable for scout camps.

To control the flame you'll need to control the 'draft', some kind of door at the front may help.

I wonder would my wife let me build one in the garden... hmmm

Kate said...

Bobby, thanks. And why ever wouldn't she let you put a rocket stove in the garden? Good luck with the build!

Anonymous said...

Oh, this is so cool! Maybe one could make the hole on top round and cook with a wook? There are tons upon tons of yummy wook recipes - heaps upon heaps more than for a skillet!

Mira

Kate said...

Mira, I've been on the lookout for a wok at a garage sale since Jen suggested it. Garage sale season is ramping up where we are, so I'm hopeful that I can find one soon. It would be great to include wok-cooked dishes in my outdoor cooking project this year.

Anonymous said...

A wok is a great idea. You may want to design a simple collar to tighten the fit between the curved surface of the wok and the top of the square masonry chiminey. Air isn't a real good heat transfer media so a snug fit is pretty key if you are looking for maximum efficiency.

I'm interested in whether you see any degredation in your masonry or brickwork from the heat.

Kate said...

Anon, I've been keeping my eye out for a wok at yard sales, but so far, no luck. We have seen some degradation in the masonry, but I suspect it's more to do with our harsh winters than with the heat of cooking. The ash is a very good insulator, so I doubt the bricks are heated very much when we use it. Also, we just haven't used it all that much, something I intend to remedy this year.

Anonymous said...

Have you tried baking on it yet? I've seen bread baked on a grill in a cast iron dutch oven and I'm curious if that might work here. I'm also really curious to hear how hot the bricks get on the outside and how fast they cool down. I'd love to try something like this but I'm nervous about how safe it would be to use wit an inquisitive toddler helper.
Thanks for the post!
Claire

Strange Angel said...

I am dancing at the precipice of moving back to the country and I would LOVE to build one of these! I do have a question, however.. How/do you clean out the ash, charcoaly bits, etc, from the pipe when you've finished cooking and the fire has died off?

Kate said...

Claire, sorry for the late reply. The bricks don't get hot at all. The wood ash is an excellent insulator.

Strange Angel, there's little ash left after a burn, but what there is can be swept out with my fingers. I just pull out the metal shelf and reach into the stove pipe.

amoeba said...

My understanding, is that to control the temperature, one does NOT control the draught. The secret to a clean-burning rocket stove is UNRESTRICTED draught. For less heat, pull back the fuel, or don't feed it in so fast. For more heat, feed-in the fuel.

If one restricts the draught, incomplete combustion occurs, the stove isn't a rocket stove.
The whole point of the Rocket Stove principle is that it is very clean, fuel-efficient and virtually smoke free. A well-designed RS uses much less wood / biomass than most other stoves, about the same as a wood-gas stove, but easier to use and make.

There is a set ratio to the height of the chimney to the diameter of the combustion chamber.
For maximum efficiency use a well-designed pot-skirt.

Details here:
http://www.stovetec.net/us/images/stories/pdfs/DesignPrinciplesForWoodBurningCookstoves.pdf

There is a rocket stove design tool here: http://www.rocketstove.org/

Anonymous said...

Very cool stove. I see that there is a lot of space between the pipe, and the surrounding brick. Do you intend to fill it with ashes?
http://www.youtube.com/watch?v=J_7sft8_Ik4

cmread said...

That is so cool, I wanted to do something like that but didn't know what exactly what to do. Now I know what I need to do. Love your blog!

Yvonne said...

Indoor rocket stoves for heating are made with a vertical fuel feed. They have a larger diameter than for outdoor cooking.

This allows putting larger pieces of wood that will self feed as they burn. That gives you time to do other things than keep feeding the fire.

I have a blog and will post about rocket stoves in a couple of days. It is http://yvonnessilverlinings.blogspot.com/

I am blogging about different types of rocket stoves, so perhaps you will be able to understand the basic design of them, and can modify them to suit your preferences.

Anonymous said...

We just built our stove in the back yard. Started out with 16 bricks but decided to put fire bricks as the base. Too low. Went back to the hardware store and bought 4 hollow core blocks. Stacked two layers with opening facing forward. This allows for plenty of space to stash twigs and kindling. I know, I know, we didn't scrounge much material, but I had already used found brick for a section of the garden. I have a "blow stick" made out of a hollow reed that I use for my Rendezvous campfires to get things going. This eliminates bending over to blow on the kindling. You can also make a pretty one out of copper tubing for the same purpose. Just remember not to inhale! I found some more pavers this afternoon and I plan on stacking them on the side to add cooking space. This project can really get you going! I love having a cup of tea in the garden and now I don't have to take my muddy self inside to brew.

Linda said...

You mentioned finding a large concrete base buried in your yard - we found a huge sucker last year too! Apparently back in the day they used to bury all their left over materials. I found tons of nails when digging up my 2 gardens, no bricks though..lol.

Wish I could make something like this - it's just me and my son and he would think I really lost it if I showed him this...lol

Love the idea and an absolute necessity for power outages!!

Vera said...

I just found this post via pinterest. We have been discussing building 2 or 3 brick rocket stoves for cooking on and it nice to see how you have done it.
I have been thinking of using and old BBQ surround that was on the property when we bought it to add a way to raise the pan for less heat intensive cooking. Would you change anything looking back on it?

Kate said...

Vera, only that I'd think twice and then maybe once more about where we situated the rocket stove. It's not too conveniently located to the house. I had plans to set myself up with a little satellite kitchen out there, but, well...the best laid plans an' all. Know what I mean?