High-efficiency wood furnaces use a process called wood gasification to achieve efficiency ratings up to 90 percent. Wood gasification also reduces the amount of particulate from the fuel and, as a result, decreases combustion emissions by up to 90 percent over a standard wood furnace.
High-efficiency wood furnaces operate by providing an exact amount of airflow to the firebox. Many furnaces are calibrated to use seasoned wood as fuel. To achieve wood gasification, the furnace must regulate the amount of airflow above and below the firebox where the wood is burning. When wood burns, volatile gases and particulate matter are released. By regulating airflow, the gas is forced into a combustion chamber specifically designed to burn the volatile gas and particulate matter.
The combustion chamber burns the volatile gas at temperatures up to 2,000 degrees Fahrenheit. The lining of the firebox and combustion chamber absorb this heat and use it to keep the keep the burn chambers at the proper temperatures for combustion. The high-temperature gas combustion sharply reduces emissions and minimizes pollution from creosote buildup. The exhaust is forced through multiple flues to heat water, and then escapes through an exhaust vent outside of the house. With most of the volatile gas burned up, there is less ash production and fewer pollutants released into the air from the exhaust.