Weil-McLain® Gas/Oil Fired Boiler, 80 Series, Model: 580, 80.6% Thermal, 82.6% Combustion (Gas), 83.1% Thermal, 85.1% Combustion (Oil) AFUE, 623000 Btu/hr Input Light Oil, 639000 Btu/hr Input Gas, 515000 Btu/hr Output BTU, 60.5 gal Capacity, 2 to 4 in Supply, 2 to 3 in Return Connection, Gas, Oil Fuel, 8 in Diameter Flue, Net BTU Rating: 386 mbh Steam, 448 mbh Water, 1608 sq-ft Area, Cast-Iron, Dimensions: 57-5/16 in H x 29-7/8 in W x 35-3/8 in D