If you've never seen rocket mass heaters, the design might look a little crazy to you at first. This is a big departure from a traditional wood-burning stove. But this is one area where the principles of permaculture have inspired a truly revolutionary new technology.
Rocket mass heaters apply some basic fire science to create a heater like you've never seen before. The process uses less fuel, generates less pollution, and operates more efficiently than any other heating technology ever developed. Used in tandem with other permaculture technologies like passive solar, you could theoretically heat your house all winter long without spending a dime.
Rocket mass heaters use a simple but ingenious design, and all of the components are easy to understand. The core element of a rocket mass heater is a big block of thermal mass. Common materials for the thermal mass are cob and stone pebbles. The thermal mass is often shaped as a sofa or bed so that the homeowner can actually sit on top of the heat source.
Within the block of thermal mass there are five primary components.
First, there is a fuel magazine, or wood feed. Rocket mass heaters operate on small sticks - not big logs - and the sticks are inserted down into the combustion chamber vertically.
Next, there is an insulated combustion chamber and heat riser. This is where the fire burns, and the exhaust from the fire is fed up into the next component, the steel drum.
The exhaust from the combustion chamber is fed up into a steel drum which acts as a reburn chamber or rocket chamber. What this means is that the chamber inside the steel drum gets so hot that the initial exhaust from the fire is literally re-burned, generating even more heat.
From the reburn chamber, the final exhaust passes through a series of ducts. These ducts are typically run through the thermal mass seating or bedding to dispense as much heat as possible to the thermal mass.
The final component is a vent to the outside of the building. The exhaust produced by rocket mass heaters is notoriously clean. In an efficient design there is little exhaust other than a small amount of CO2 and some steam.
Rocket cooking stoves, which originated this technology, have been around since the early 1980s. Ianto Evans first applied the technology to heating buildings in his 2006 book Rocket Mass Heaters.
In the years since Evans' book, the technology has been put into practice around the world, and several designs have been approved for safe use by various government regulatory agencies. Whether or not it is legal to build a rocket mass heater in your home will depend on the laws for your particular jurisdiction.
There are plenty of resources available if you want to learn more. In addition to Evans' book mentioned above, Ernie and Erica Wisner wrote a great book on the topic called The Rocket Mass Heater Builder's Guide that was released in 2016.
And if you want to see the construction process first-hand, you should check out Paul Wheaton's video series called DIY Rocket Mass Heaters. You'll see the building process for several different styles, and a unique perspective on the "Innovator's Event," where Paul hosted several of the leading experts on rocket mass heaters and asked them to push the envelope on design and materials.