Rocket Stoves

A couple of years ago, when we started investigating the Maker Movement or DIY Movement, I came across sites that explained how to build an extremely efficient stove out of cans – called a Rocket Stove.  My son and I made one out of galvanized steel duct pipe (made for clothes drier exhaust), which was a big mistake for health reasons.  The zinc in the galvanized layer doesn’t get hot enough to cook off as a gas if those are used as drier ducts, but if exposed to a hot fire, it could create zinc oxide gas, which causes Welder’s Fever (which can be fatal).  Either we didn’t get it hot enough, or because we had it mounted in our fireplace, the bad gas went up and out – and not into us.  Anyway, don’t make our mistake – don’t use zinc-treated metal for this.  The risk isn’t worth it.  Also, please be very careful and use basic fire safety:  if you’re a child, please get a responsible adult’s permission and help before trying anything like this.  I also recommend reading many other sites on rocket stoves and safety, and take a class from a maker club in your area if you have no experience with this – a class that includes safety training.

So, what is a rocket stove, and what’s the big deal about it?

Well, the sites I read explained that in the developing world it’s common for people to cook in their homes using the three rock method, i.e. they build a campfire on a hearth in their house (often with no chimney!) and use three rocks to hold up their cooking pot over the flames.  This kind of open fire is very inefficient and requires actual firewood (like split wood from a tree trunk – or decent sized branch wood) – which means that people all over the world are destroying their forests just to cook dinner.  It also means their houses are filled with dangerous smoke, giving them all sorts of health issues.

A solution is to change how they cook, and a great option is the rocket stove.  It’s also a great thing to make (please be safe!) and have ready in case of an emergency (like the power is off for a long time and you need to cook).  Rocket stoves only require dry trash wood, sticks, stems, cardboard or even heavy grass to work.  You don’t need to kill a tree to cook on a rocket stove:  the sticks that fall off trees are enough.  Also, because rocket stoves actually concentrate and burn the smoke in the riser, there’s very little smoke – so they pollute little and cause fewer health problems.  I wouldn’t use one indoors, but in the developing world, if a family is already using three-rock fires indoors, a rocket stove would make a heck of a lot less indoor pollution.

Here’s a diagram:

rocket stove for blog

This is a basic L-shaped Rocket Stove.  The sticks are fed in on top of the shelf, and while some air flows in with the sticks, the important air for the fire rushes in under the shelf.  The hot gasses going up in the riser (chimney effect) causes the air to rush in, and because the space is restricted, the air speeds up (ventury effect) – making a rockety sound (which is why it’s called a rocket stove).  You can add a slightly larger metal cylinder around the riser and fill the gap with a non flammable, low density insulating material, like Perlite or ash.  This makes the stove burn more efficiently, because less heat escapes out the sides of the risers – and goes up to your cooking pot (which has to be positioned at least a few inches above the top of the riser).

Our first rocket stove worked.  In about five minutes and using only a handful of sticks from the yard, my son and I got a corn can with 9 or 10 ounces of water in it to reach a hard boil.  I was amazed.  And it made the sound of a rocket engine, which was very gaaf (cool)!

Since then, we’ve experimented with gravity-fed rocket stoves, also called J style.  It’s hard to keep the fire from burning up the fuel, even when you use a sealed (or is it sealed?) feed tube, to try to keep oxygen out of the feed tube.  We’ve also experimented with TLUD stoves or Top-Lit Up-Draft – where you basically gassify trash-wood or wood pellets for a quality, relatively clean burning flame.  It’s been challenging for us to get those to burn long enough to boil large amounts of water (a gallon or more), but we can bring 2 cups or a quart to a boil in 5 to 10 minutes.  Another problem these stoves have is that they generally have one temperature:  blazing hot.  So it’s hard to simmer or do other low heat cooking, except there’s got to be a way to shunt off part of the heat for this purpose.  We’re still working on this.

There are commercially made rocket stoves, if you want to buy one and try it out.  There are also commercially made TLUD and TLUD like stoves, if making one seems like a bad idea for you.  I’d encourage you to look into making one, but again, please be sure that you have the necessary skills and understanding of safety before trying this.  You’re responsible for the safety of you and the people around you when you work with metal (which can have sharp edges or give off toxic gasses), and any time you work with fire, there’s a danger.

In the novel, Steemjammer, we meet people who live in a world of steam that has developed into a world kind of like ours – but it’s also one without a central government or much sense of safety.  The advantage of this is that people are free to do what they want, and society benefits from increased innovation and entrepreneurship.  The downside is that they have a lot more accidents, including accidental deaths, that could have been avoided.  Like generations past in our world, the members of this steam society are tough and just consider risk (and accidents) a part of life.  If you never met a person born before 1900, you might have trouble believing that our older generations didn’t care much about safety (compared to our hyper-safety levels – they did care some), but it’s true (if you talk to enough construction workers, for instance, you’ll come across this attitude, even today).  Personally, I’d learn as much as I could about safety before undertaking any project involving metal work or fire.  If you do it right, it’s possible to keep accidents down to the level of minor cuts and bruises – while learning how to do amazing things, like boiling water with a handful of sticks (something you could never do arranging these sticks in the style of a campfire, for instance).  Good luck and please be safe!

(Also, if you’re interested in steam engines or boilers, please don’t make one unless you really, REALLY know what you’re doing.  They say a gallon of water in a steam boiler can have as much energy as one stick of dynamite.  In the steam era, many people died from steam boiler explosions.  They’re incredibly dangerous, even if you are trained to use or make them.  I’m sorry to sound paranoid, but when it comes to steam power, you can’t be careful enough.)


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