Rocket Mass Stoves are used for interior heating, and are now starting to appear around North America and Northern Europe. They have real promise, in that they significantly reduce the amount of fuel burned, thereby lessening the load of CO2 on greenhouse gases. They capture almost all of the heat from the wood that is burned, as opposed to a classic wood burning stove, which often reaches temperatures of 600 degrees F and above in it's chimney, signifying that much of the heat is going up and out.   When a thermal mass system is built around the rocket stove's exhaust, the mass can store almost all of the heat generated for a long, slow release.  A Rocket Mass Heater may only need to be fired for an hour or two, just once or twice a day, depending on the outdoor temperatures and how well the space has been insulated.   Additionally, built with a special cob mix, it can be sculpted to create custom seating for the space it occupies.