Wood furnaces using technology designed and refined during the 20th century offer high efficiency ratings. Fireplaces and older wood furnaces are some of the least efficient sources of heating.
Most of the heat generated in fireplaces leaves through the chimney, while wood-burning furnaces capture more of this heat. Advanced furnaces offer cleaner combustion that can improve overall system efficiency by 50 percent, letting them capture most of the energy stored in wood.
In environmental terms, wood-burning furnaces release far more particulate matter than oil and gas technology, which can lead to localized health problems. Advanced systems are still more damaging than systems using other fuels.