Rocket Mass Heaters: Efficient domestic hot water and air. A look at stove designs across the world.

Title image Rocket mass heaters


Rocket mass heaters or rocket stoves have all the benefits of a fireplace or wood stove while only using one fifth the wood . The rocket stove framework can be adapted to burn pellets and other fuels as they are on a basic level an incinerator. They also are easily designed into beautiful furniture or partition walls. Further they can be integrated into water heating systems and are very efficient to the point where a person can put their face over the chimney with little discomfort during regular operation.  Optimal fuel for these stoves is to burn small twigs and branches making it quite reasonable to collect enough wood for the winter from basic clean up.  Planning to grow specific trees and bushes designed for annuall pruning provides for the required amount of wood to get through the seasons. by design. This expression of responsible subsistence coupled with intelligent design is a perfect example of core principals of awaytogether.


Rocket denotes the sound made  air whooshing through the firebox.

Consider most wood fireplaces in comparison are passive with the wood cracking, flames flickering smoke wafting  up the chimney.
Compare this to the rocket stove which is like hitting the gas in a vehicle while your going downhill, once the fire is going the drawing force of the chimney causes an acceleration of incoming air into the firebox causing more chimney gas thus ramping up the system like a jet engine, or even dare we say… a rocket.


Mass denotes the bulk material used as heat storage. Like a mass of people at church gets the place feeling warm so does the mass in a rocket mass heater. The rocket part provides the heat; the mass in this application is known as thermal mass. Thermal mass is the hot pot of soup, the warm sunny side of a brick wall, a hot water bottle or simply a hot black rock.  The rocket stove incorporates this principal into a bench made of concrete, adobe or even simply a plywood box of gravel. It’s just has to function as a way to hold and release heat. Heat moves from hot to cold so as we say, make hay while the sun shines cause when the fires out the thermal mass continues to pay out with stored heat from it’s thermal mass.


Heater denotes the design and construct of something that makes and delivers heat in a safe and efficient fashion.  There is a big difference between starting a wood gobbling fire in a box and a elegantly designed system that scrubs most of the heat from the fire and smoke before delivering the exaust to atmosphere.


If you think rocket stoves are revolutionary you might want to look into…

Russian stoves title image

Russian stoves have all the features of rocket stove and more all packed into a beautiful marriage of form and function. However these stoves are skill level 5 so you might need to brush up on your masonry skills to build one of these.

We finish with an article quoting Mark Twain contrasting Western “fireplace” wood stoves and  European masonry stoves


“Take the German stove, for instance – where can you find it outside of German countries? I am sure I have never seen it where German was not the language of the region. Yet it is by long odds the best stove and the most convenient and economical that has yet been invented.

To the uninstructed stranger it promises nothing; but he will soon find that it is a masterly performer, for all that. It has a little bit of a door which you couldn’t get your head in – a door which seems foolishly out of proportion to the rest of the edifice; yet the door is right, for it is not necessary that bulky fuel shall enter it. Small-sized fuel is used, and marvelously little of that. The door opens into a tiny cavern which would not hold more fuel than a baby could fetch in its arms. The process of firing is quick and simple. At half past seven on a cold morning the servant brings a small basketful of slender pine sticks – say a modified armful – and puts half of these in, lights them with a match, and closes the door. They burn out in ten or twelve minutes. He then puts in the rest and locks the door, and carries off the key. The work is done. He will not come again until next morning.

All day long and until past midnight all parts of the room will be delightfully warm and comfortable, and there will be no headaches and no sense of closeness or oppression. In an American room, whether heated by steam, hot water, or open fires, the neighborhood of the register or the fireplace is warmest – the heat is not equally diffused throughout the room; but in a German room one is comfortable in one part of it as in another. Nothing is gained or lost by being near the stove. Its surface is not hot; you can put your hand on it anywhere and not get burnt.

Consider these things. One firing is enough for the day; the cost is next to nothing; the heat produced is the same all day, instead of too hot and too cold by turns; one may absorb himself in his business in peace; he does not need to feel any anxieties of solicitudes about the fire; his whole day is a realized dream of bodily comfort.

America could adopt this stove, but does America do it? The American wood stove, of whatsoever breed, it is a terror. There can be no tranquility of mind where it is. It requires more attention than a baby. It has to be fed every little while, it has to be watched all the time; and for all reward you are roasted half your time and frozen the other half. It warms no part of the room but its own part; it breeds headaches and suffocation, and makes one’s skin feel dry and feverish; and when your wood bill comes in you think you have been supporting a volcano.

We have in America many and many a breed of coal stoves, also – fiendish things, everyone of them. The base burners are heady and require but little attention; but none of them, of whatsoever kind, distributes its heat uniformly through the room, or keeps it at an unvarying temperature, or fails to take the life out of the atmosphere and leave it stuffy and smothery and stupefying….”

a note on safety with Lumpy the Rocket Log…

Cartoon of Log riding a rocket


Designing and building anything that burns gas,wood or anything else has many potentials of disaster. Using an improper material such as galvanized tin pipe such as used for forced air heating will lead to creation of poisonous zinc gasses. This galvanized tin pipe when heated to temperatures encountered with wood burning stoves causes the zinc coating to oxidize causing an illness called Metal Fume Fever.  Be sure to follow a well proven design or if you are going to venture to make do with what you got it is best to build the core of the stove in an area where is can safely be tested for effective venting of combustion gasses and endurance of materials under high temperatures.


Still hungry for more rocket mass heater subject matter?

Check out Geoff Lawtons presentation on a very functional farm built rocket mass water heater at Zaytuna Farm.