Due to recent EPA regulations on the wood burning stove industry, utilizing the process of wood gasification in indoor and outdoor wood stoves has become increasingly common. This is because this process creates far less smoke and soot, namely carbon emissions. I'll explain how it works.
Every element has a gaseous state, meaning that if any item is heated to a high enough temperature, it will be turned to a gas, which burns much cleaner than a traditional burn. That is the basic concept behind wood gasification outdoor boilers. Wood is placed in the fire box and lit while the draft is flowing out through an exhaust hole in the top of the fire box. Once the wood has lit sufficiently, the exhaust hole is closed and the draft is forced down through slot in the fire brick, which is super heated by the fire. The heat from the fire brick heats the wood above causing it to turn to a gas, which is then burnt at a temperature in excess of 3000 degrees Fahrenheit. The remaining exhaust is sucked out the chimney by a draft inducer fan. This process causes much greater energy efficiency and far less carbon emissions than a traditional burn.