Learning about the Rocket Stove

Burn chamber view

I have been experimenting with Rocket Stoves in an effort to build a rocket stove BBQ grill.  Well actually, I want to use it for a bunch of different types of outdoor cooking.  This post will be the first in a series of posts that walk you through my experimenting with the rocket stove.

A rocket stove is an efficient cooking stove using small diameter wood fuel which is burned in a simple high-temperature combustion chamber containing a vertical chimney, which ensures almost complete combustion prior to the flames reaching the cooking surface. Wikipedia

My ultimate goal is to build a permanent installation with a rocket stove as the heat source, but with a number of different options for cooking.  These options could include a BBQ grill, indirect heat grill, rotisserie, burner, and maybe even a pizza or bread oven.  To do this, I am going to have to start small and build my personal knowledge.  I have done a lot of research along the way, and looked at a lot of other people’s designs.  If you are interested, the Design Principles at rocketstove.org is a good place to begin.   I begin with a 4 brick stove that I will discuss in this article, and end up with a relatively flexible system that allows me to adjust bricks to customize the way I use the heat.  Along the way, I will have a handful of articles where I will share what I have done and learned.  I hope you enjoy.

Four Brick Basic Rocket Stove

Let’s start this out by saying that I did not have a budget for experimenting with rocket stoves.  That doesn’t mean I had an unlimited budget, it means I had no budget.  Most of what I do is done with bricks and cinder blocks (concrete blocks) I had around the house.

The most basic design can be built using 4 concrete blocks.  It is a basic design that requires either an “H” block or, as I did, knock one end off of one of the blocks.

4 brick rocket stove design
This shows the basic 4 brick stove design.

The first brick is simply there as a base.  I placed it so the air chambers went from side to side.  On top of this, I placed another brick that I customized by knocking the end off so that I could create a right angle for the burn chamber.  In front of the first two bricks, another brick is placed standing on end so that the openings go from the front, forming the burn chamber with the section of the second brick with the end knocked off.  The fourth brick is used to create the chimney above the burn chamber.  In the picture I have it overlapping the second and third bricks.  I did this so that it stabilized all the bricks together.

Basic chamber view
The top opening of the brick standing on end creates the opening for the wood and entrance for the burn chamber.

In the image above, you can see the burn chamber.  The  wood is placed through the top hole in the brick placed on end and into the second brick through the space where the end was knocked off that brick.  From there, the heat and smoke go straight up the chimney and out the top of the stove.  In some of the things I have read and seen, they use a shelf that the wood sits on, and allows the air to go underneath the wood into the burn chamber.

Top front view
This image shows the stove with the additional air chamber installed.

In some of the things I have read and seen, they use a shelf that the wood sits on, and allows the air to go underneath the wood into the burn chamber.  This image and the next show this kind of design.  From what I have seen, there is some debate about whether this is the best way to do it.  I haven’t taken a scientific enough approach to this to be able to answer that question.  The important thing is that the air needs to have plenty of room to come into the burn chamber, past the ends of the wood that are burning in the burn chamber, then out through the chimney.

The key is to have enough air going through the burn chamber and chimney to burn very hot, and in the process burn the smoke so that almost no smoke ever comes out of the top of the chimney.  Again, there are a lot of opinions about the best way to do this, but the things that appear to be agreed on are that the burn chamber needs to get hot, and the fire needs to go up into a chimney and burn through the chimney.  In the best designs, most or all of the smoke will be burned, and that is where the efficiency comes from.  Smoke coming out the chimney represents wasted energy since it did not burn.

Burn chamber view
This shows how the shelf allows the air to come in under the wood.

From what I have learned, this L shaped burn chamber with the air coming in under the shelf gives the person running the stove the greatest control of the burn, and subsequently also is the most efficient.  The draw back is that the wood has to be constantly shifted to keep fresh wood in the burn zone.  I think overall, that is one of the greatest issues with the rocket stove.  Not a problem, just something that needs to be considered when you are designing your stove.

Fire coming from chimney
This one shows the fire coming out of the chimney.

One of the things that I found with the four brick stove is that it is hard to get the burn chamber hot enough to get to a point of efficiency.  In the next article, I will start working with the use of a tube inside the chimney to minimize the amount of block being heated up, and hopefully increasing the efficiency of the unit.

So, what I learned here, is that the most basic form of rocket stove will work.  I did not try using it for anything, but this model would be relatively limited, perhaps the best use would be for a burner.  It wouldn’t be big enough for grilling. In a later article I will build a prototype which will be  built around a J shaped intake, combustion chamber, and chimney.  In the next posting, we take a look at the role of the chimney.

Garden Crap

old wood bench

I’ve come to realize that this is a vanity blog.  That means that I can write about anything I want, when I want.  So tonight I am going to write about a garden crap bench I made for my wife.

Tina is a funny sort.  She doesn’t care for gardening.  But she likes all that crap that people put in their gardens.  You know like the little statues and creatures and stuff like that.  Garden Crap.

Garden with lawn ornaments
This is the spring ’15 layout of Brayden Garden

So, yesterday I decided to make her some garden crap.  Mostly she likes stuff with rust and decaying wood and such.  So I took some really old wood and put it together into a little bench.

old wood bench
The garden crap bench I made for Tina.

I did it as a way of saying I love you!



Day 38

Compost piles are food for your garden, the evolution of my compost pile

Compost pile

For most people, the compost pile is not something worthy of a blog post.  But for the true gardeners, there is an understanding that the compost pile is the heart of the garden.

At the most fundamental level, composting is easy.  You throw a bunch of organic matter in a pile and leave it there to rot.  But as you spend more time gardening, and seasons composting, you start to learn that there is composting and then there is composting.  I am not going to go into the chemistry and process of composting.  I have nothing to add that hasn’t been spoken about before.

But what I can do is share with you the evolution of my composting pile.  When I first started out I decided to use a wire frame cylindrical frame.  This was easy to set up and did a good job of containing the compost, but it was hard to mix, and the good stuff was down at the bottom out of reach.  That combined with placing it in a shaded area meant I didn’t get the results I wanted as fast as I wanted.  I needed more compost than I could produce, so I moved on.

Wire Bin Compost Pile
This wire circle was my first compost pile. I made the mistake of putting it in the shaded corner of the yard where it didn’t get enough light to really heat up.

The next evolution of the compost pile found me out in a sunny area.  I had learned about the three bin method, where you migrate the compost from one bin to the next as it aged.  This process allows you to turn over the pile and aerate it as you move it from one bin to the next.  And that is the way to keep your compost hot, make sure it gets plenty of air down in the composting materials.  You also need to have the right combination of green and brown materials, but the real key is air and moisture.

Pallets used to make 3 bin compost pile
The pallets were used to create a three bin compost pile.

This worked pretty well, but I still found myself needing more compost than I could produce in this way.  So, I went to the next version, they straw bale enclosure.

The idea behind the straw bale compost is pretty easy.  You use straw bales to build the container that the compost goes into.  This provides a barrier that helps keep the heat in during the colder months so you can compost when other methods would have shut down.  Along the way, the straw bales start to compost themselves and provide additional carbon materials (brown) to the compost pile.  I would cover it with a black tarp to trap in the heat and keep out excess water, and I would hold the  plastic down with, you guessed it, old pallets.

straw bale compost
This shows how the pile covered in plastic.

I got a couple of years out of the straw bales, but they eventually broke down into compost. The image below shows it the second and last year that I used straw bales.  That year I decided that I still needed more compost than I was producing.  That fall, after watching truck after truck drive by bringing leaves to the dump, I decided that it was silly for them to drive by my house on the way when I could use them for my compost.  So, I invited a few of the neighbors to bring me their leaves and I ended up with a much bigger compost pile, and a tradition that continues today.

Straw bale compost pile
The straw bales break down and the pile becomes less contained.

I now had a reasonable amount of compost, and it allowed me to leave some there during the year.  And what I found out, is that during the summer, the location that normally holds the compost pile, really want things to grow.  So I have experimented with things like potatoes, and squash, pumpkins and tomatoes, and really anything that wants to grow there.  At the very least, it will become next year’s compost.

Plants growing in compost pile
For some reason, things want to grow in my compost pile.
Plants growing in compost pile
Another view of the compost pile in relation to the rest of the garden

This last fall I went all the way and put up a sign that said “taking leaves” beside the road inviting the entire neighborhood to bring in their leaves.  And several did.  I ended up with a very large compost pile.  It is big enough now that it takes up the whole area behind the white fence, and is about 5 feet deep in the fall, and about 3 1/2 feet deep in the spring.  Then a couple of weeks ago I had a friend call and ask if they could bring in their leaves, grass clippings and pine needles to throw on my pile.  “Well yeah!”

So now I have this really massive compost pile.  It is a bit of work to turn it over, but I do that to keep it composting hot.  Last Sunday I reached my hand into the middle of the pile and it was HOT!  That is exactly what you want.

Big Compost pile
The pile at the beginning of spring, and before a friend brought in another truck load of stuff.

I think this year I may have enough compost.  It still has some rotting to do, but another 4 weeks and it should be mostly ready to spread.  And my garden is going to love it.



Day 24