A rocket mass heater is a system that typically burns wood more efficiently than other types of stoves. It usually emits exhaust that is made of steam and carbon dioxide, instead of smoke made of particles and gases that some stoves release without being burned. The rocket stove is often built as part of Do-It-Yourself (DIY) projects. Wood branches or sticks are typically placed into a chamber, and flames usually burn sideways at the bottom. Often built with bricks, the stove also has a combustion chamber that can have a J-shape, and which is often covered by a container such as an oil drum.
Gases in the rocket mass heater burn in the combustion chamber. Once reaching the top, they can be forced between the outer container and a layer of insulation. The hot gases then usually flow into a horizontal pipe. Heat can be stored in this area and released into a room over time. Wood used for the system is often claimed to be consumed at a fraction the amount of other types of stoves.
In a rocket mass heater, flames can burn for days at a time. Conventional stoves often cost a significant amount of money, sometimes thousands of dollars. The rocket stove is usually a fraction of the cost and many people claim to have built one within a couple of days. It can be built with common materials, such as brick, drums, and pipe. The thermal energy storage component, which surrounds the metal duct pipe, is sometimes integrated into the buildings supporting structure.
A smaller version, called a pocket rocket, typically does not have thermal storage, but can still provide enough heat for a small space. Local and regional building codes generally do not cover rocket mass heater designs, making it difficult to efficiently integrate one with a chimney, for example. While some smoke can be produced when the rocket stove is started, the heating system most often burns clean. Many people have used them in cities as well, often avoiding discovery by regulatory agencies because the emissions are minimal and typically undetectable.
The temperature of the gas in a rocket mass heater is usually lower in comparison to other heating systems. Steam can condense into liquid, releasing latent heat as well. Some builders and experts have written books that instruct on how to build a rocket stove, which is often used in North America and Europe for heating as well as cooking.