For those who want to burn cordwood, modern wood-gasification boilers offer mid-80% steady state combustion efficiencies and full-cycle efficiencies in the range of 70% to 75%. This is much higher — almost double — the average burn cycle efficiencies achieved by outdoor wood-fired furnaces using single-stage combustion.
Modern biomass boilers are as different from earlier generation wood-burning boilers as smartphones are from their rotary dial predecessors. For example, modern pellet-fired boilers can operate unattended for several weeks. They automatically convey pellets from bulk storage to their combustion chamber, ignite them and modulate the combustion process based on water temperature and the oxygen content of the exhaust gases. Some models even compress the small amount of ash produced, which lengthens the time between cleanings.
