don't go up in smoke! Gasification boilers vs outdoor boilers

When it comes to cheap, easy heat in rural areas, there seemed to be a continuing trend towards outdoor boilers. These "garbage disposal" type wood burners are touted as being able to burn "anything" from freshly cut wood to scap lumber. Unfortunately, these "wood doctor" type boilers are anything but cheap and easy. They are notorious smokers that never seem to offer an efficient burn; efficiency rarely above 50%. Combine that with household garbage that is sometimes disposed of in these units and you have a particularly toxic and polluting heat source.

Then comes the gasification boiler or furnace. These newer boilers use the latest in combustion technology; beyond the "secondary burn" technology offered in woodstoves which has been a huge benefit in home heating.

Where the difference lies between "secondary burn" woodstoves and "gasification boilers" is the temperature at which the fuel is burned. In standard wood burning appliances, it is well known that higher temperatures = cleaner burn. Hence the catalytic converter inserted in some woodstoves. The problem with woodstoves and most outdoor boilers is that they cannot effectively raise the temperature of the combustion chamber without damaging the firebox itself; not above 800°F in a woodstove and 500°F in an outdoor woodboiler.

Gasification boilers operate with a slight difference. First they combust the fuel source (wood) in a low temperature primary burn chamber. This releases all the fuel from the wood in the form of smoke and other gases. Then fresh "super heated" air is injected into this "smoke" as it enters the secondary burn chamber which is lined with refractory brick. This allows the burn temperature to rise above 1800°F offering a clean and efficient flame. All fuel that has been released from the wood is being burned without the use of a catalytic converter. These boilers/furnaces can reach efficiencies above 95% vs 70% for top quality wood stoves and 45-50% for the average outdoor wood boiler. This can equate to a fuel wood savings of hundreds of dollars or many, many cords of wood. If you burn 5 cords of wood in an outdoor wood boiler, you would use 3 1/2 cords with an efficient wood stove or just over 2 cords with a super efficient gasification boiler. Now you see why "cheap and easy" isn't so "cheap and easy"?