Williams & Davis Boiler – 500 HP. Model: 500-777. National Board: 4716. Capacity: 16,738 MBH. Heating surface (Fire side): 2,500 sq. ft. Heating surface (Water side): 2,748 sq. ft. Number of tubes: 234. Tube dimensions: 2-1/2 in. dia. x 16 ft. 8 in. L. Steam output: 17,250 lbs./hr. MAWP: 150 psig. Gas burner BTU input: 21,000,000 btu/hr. Oil burner: 150 gpm (No.2 oil). Control voltage: 120 volt. Motor voltage: 480 volt, 3 phase. Estimated shipping weight: 48,500 lbs. Overall dimensions: 24 ft. 6 in. L x 8 ft. 10 in. W x 9 ft. 4 in. H. (ACN1360)