A rocket mass heater is a space heating system developed from the rocket stove, a hybrid with elements of an efficient wood-burning stove and a masonry heater. Wood is gravity fed into a “J-shaped” combustion chamber, from where the hot gases enter a heavily insulated metal vertical secondary combustion chamber, the exhaust then passes along horizontal metal ducting embedded within a massive thermal storage.
The thermal storage is large enough to retain heat for many hours and typically forms part of the structure of a building. Rocket mass heaters have proven to be popular with natural builders and within a permaculture designs. They are normally self-built and are not yet recognized by all building codes which regulate the design and construction of heating systems within buildings.
The rocket mass heater works on similar properties as a masonry heater. A fast, high heat and oxygen-fed fire burn up the volatile gases and particulates, leaving very little pollution, and turn almost all the fuel into energy. A bit of smoke is released during the first minutes of a fire, until the temperature in the chamber is hot enough to burn all gases.
The major difference between a masonry heater and a rocket, is that the rocket stove has an insulated J- or L- shaped combustion chamber that forces the fire to burn horizontally. The fire then hits a 90 degree angle at the end of the chamber which causes a strong turbulence to rise up the insulated heat riser, creating a strong draft that feeds the intensity of the fire.