What causes wood smoke?
Wood releases its volatile compounds when heated. Most of these compounds require at least 1,300°F to combust. They also store between 50%-60% of the total energy contained in the wood. If the fire is not hot enough, the energy from the volatile compounds will be lost as smoke with it's accompaning air pollution and creosote danger.
A wood-fired combustion zone can be cooled to below the required temperatures for combusting smoke in a variety of ways. For example, too much cold air being introduced in an open fireplace. Or, using heat-conducting materials such as cast iron in the combustion chamber. Many barrel stoves and cast iron stove designs include this flaw. While it seems like a good idea to harvest the heat from the combustion proces, this is actually counter-productive, because it cools the combustion zone. A cooler combustion zone results in smoke and reduced efficiency.
It follows, then, that the hotter the fire, the more complete the combustion, the higher the efficiency of the burn, and the less wood you have to chop.
To insure a hot burn, the Dragon Burner primary combustion chamber (shown in the illustration as the horizontal tan component) is cast from an insulating refractory material. Since this chamber gets very hot, the expanding gases are forced out of the burn tunnel prior to combustion being complete. Therefore a second insulated combustion chamber (the heat riser, shown in blue) completes the combustion process.
The importance of turbulence in burning wood
The fire in the burn tunnel consumes the solids and releases the wood's volatile compounds. In addition to an insulated combustion zone, the Dragon Burner increases efficiency by insuring that all the exhaust gases are adequately mixed with oxygen from the supply air by creating turbulence. Peter van den Berg, an experienced designer of masonry heaters and rocket heaters, developed the Dragon Burner design. Read more about the turbulence design elements here .....
There is no smoke or pollution emitting from your stove pipe because all of the components of the wood are consumed. There is also practically no ash because the solids are consumed as well.
Burning Softwoods and Conifers
Because the combustion process is so complete, you can use “pitchy” woods, such as pine, in your Dragon Heater. All the compounds which would normally accumulate in your “chimney” never get there because they are consumed by the very high temperatures.
Using the heat
Once the combustion process is complete and the exhaust gases leave the heat riser, heat extraction can begin. Heat extraction can be approached in two ways depending on the heating requirements of the space.
The first approach is to put the heat out into the space immediately. The "Tiled Rocket Heater" build is an example. If you want to learn more about its advantages and disadvantages, refer to
The castle build is an example of the second approach, which attempts to capture the heat using appropriate materials for slow release over time.