90 percent to 98.5 percent. annual fuel utilization efficiency annual fuel utilization efficiency residential furnace unit according to the US Department of Energy furnace or boiler Annual Fuel Utilization Efficiency annual fuel utilization efficiency Regular maintenance of a furnace "Heat & Cool". In a furnace up to 35 percent Furnace Replacement energy efficient furnace that saves you a lot of money Furnace Replacement informational page from the U.S. Department of Energy Energy.gov page  furnace or boiler excessive costs AFUE space-heating equipment AFUE US Department of Energy residential furnace unit AFUE ratings annual fuel utilization efficiency Learn more about furnace energy-efficiency 56 percent to 83 percent AFUE a furnace or a boiler 80 and 83 AFUE energy efficient furnace that saves you a lot of money AFUE ratings AFUE rating space-heating equipment boiler efficiency ratings https://energy.gov/energysaver/furnaces-and-boilers furnace Regular maintenance of a furnace http://energy.gov/energysaver/furnaces-and-boilers Energy.gov energy efficient A boiler Annual Fuel Utilization Efficiency energy consumption energy.gov Furnace Replacement Energy.gov Department of Energy Energy.Gov Energy Saver Furnaces heating system within your home 56-70 AFUE heated by either a furnace Boiler and Furnace Replacements condensing furnaces and boilers According to the U.S. Department of Energy (DOE) Energy.gov heater/furnace Furnace Replacement Regular maintenance of a furnace could be major annual fuel utilization efficiency annual fuel utilization efficiency energy efficient efficient gas furnace for a heating system tips 90-98.5 percent AFUE Department of Energy Department of Energy page  space-heating equipment Energy.gov U.S. Department of Energy website furnace Energy.gov AFUE According to the U.S. Department of Energy (DOE) federal government Vintage boilers Use this page http://energy.gov Annual Fuel Utilization Efficiency type of furnace Energy.gov estimate the savings Boiler and Furnace Replacements annual fuel utilization efficiency Energy.gov space-heating equipment boiler AFUE ratings Furnaces and boilers vast majority Annual Fuel Utilization Efficiency energy.gov U.S. Department of Energy recommends Regular maintenance of a furnace