Not too long ago, I wrote a review of a book, and I slammed it. I slammed this particular book because they screwed up rocket stoves.

Yeah, petty… slamming a piece of literature for messing up a technical detail. Usually, I’m not that guy (okay, I’m always a little bit that guy, but often not too severely). Here’s the thing, it was prepper fiction, and the main thing that it had going for it was technical accuracy. It was terribly written, terribly plotted, nothing much happened story-wise. Then they went and screwed up how rocket stoves work to the point where someone following their advice would not have created a functional stove.

This article isn’t going to be a tutorial on how to create a rocket stove (you can find that here); instead, it’s going to go into the principles involved and what makes them work — why they are such a fantastic piece of survival technology, especially if you are trying to prep on the cheap!

What is a Rocket Stove?

A rocket stove is a wood burning stove that uses a “rocket” effect to burn incredibly hot. Rocket stoves burn so hot that they burn the carbon in their own smoke, resulting in a nearly smokeless fire once they are at full heat. I have heard of people firing ceramics with a rocket stove. There is a popular method for using a rocket stove to heat a small house. They can use just the deadfall from the average suburban lot to heat a little, well-insulated home. This is called a Rocket Stove Mass Heater, and I will be going into more detail a bit further down in this article. There was a post online where a couple had constructed a hot-tub out of an old barrel and used only a rocket stove to heat it. I can’t find it at the moment, and the ones I can find are terrifying — I can’t recommend any of them without trying them myself.

The Core Principles

A rocket stove is a stove with a burn chamber that is extremely well insulated, and a feed slot that is open for you to push new fuel inside that is low on the stove, typically horizontal to the burn chamber floor or maybe slanting slightly down. There is also a wide chimney for heat to leave by.

The well-insulated burn chamber lets the fire become incredibly hot very quickly. The feed slot (where you push the wood in) being near the bottom means that you also have air drawn in from near the bottom at the side. The wide chimney means that air will be drawn in fast and will shoot up the chimney rapidly. The area right above the chimney is incredibly hot. One side effect of this is that small fuel (twigs and the like) work just fine. You are burning everything with much higher efficiency than a regular fire.

When a rocket stove gets going, you will hear a roaring whooshing sound. That sound means your fire is up to heat.

In addition to smaller items, some wetter twigs are not going to make a massive difference to your end product.

Materials

I have personally made rocket stoves out of tin cans I got out of the garbage as well as out of a large oil barrel and some piping. The tin can method is the best-known one, although oil barrels are typical. Everyone I have ever known who has made a rocket stove has used ash for their insulation. It’s a perfect material since it won’t burn no matter how hot things get, won’t explode, and is an excellent insulator. You do need quite a bit of it, but it’s ash. Just collect it when you make a regular fire or have a barbecue is you use charcoal.

It’s very, very important that you not allow any charcoal to get mixed in with the ash. That could be bad…

I have seen pictures of rocket stoves in sub-Saharan Africa made out of cinder blocks. They do the trick quite nicely.

What are They Good For?

Rocket stoves are pretty good for cooking. You can boil water very rapidly, cook meat, whatever. You need to put some sort of grill a bit above the chimney, but that’s not a problem.

As I said in the intro, you can use them for firing ceramics. That’s a tricky prospect, but it will work.

Rocket Stove Mass Heaters

Mass Heaters are a primary reason why rocket stoves are so popular with off-grid types. The rocket stove mass heater involves making a large rocket stove, say oil barrel size, and requires a number of other steps.

A Rocket Stove Mass Heater involves both the rocket stove itself and a large cob bench as well as a long pipe for the chimney. The long pipe is going to be laid along the floor and lead outside of your house. Now, this works best with something like a cob home with a small central area that is your primary area for heating. You build the chimney into a cob bench. As you run the stove (it’s common to have some sort of valve that switches between running the exhaust from the top of the stove to the longer pipe so that you can still use the stove for cooking) with the exhaust going through the longer chimney the bench heats up. It will then radiate heat for many, many hours afterwards. Typically for a small cob home, you will need to run the stove for half an hour every twelve hours.

Rocket Stove Hot-Tubs

There are a bunch of designs for hot tubs. The sane ones use the same principle as the mass heater, running the exhaust through water to heat it. Some of the crazier ones have the rocket stove right under the hot tub. I would worry about accidentally cooking myself!

Anything Else That Requires Heat

The rocket stove is very efficient at creating heat. Tapping into that heat isn’t hard. You can put an oven above the flame. You can pipe the exhaust through stuff. It’s getting the most heat out of the fuel.

What This All Means

Rocket stoves are one of the best sustainable technologies out there. They use minimal fuel and create incredibly hot fires easily. They can be built with almost no cost (the tin can ones I’ve made have all been cans that someone else was throwing away).

This is the basic design I used for my first few rocket stoves. I did use ash for the insulation, and they appear to be using just an air gap. Ash is a better option, in my opinion, although an air gap will work.