Among the outstanding features which characterize this boiler installation is a capacity of each of the two units in excess of 1,000,000 lb per hr. The direct-fired, slag-tapped furnace with a twin arrangement of sectional header boilers above a single furnace is an innovation. The building that houses the two boilers, bunkers, and all auxiliaries is 78.7 ft by 106.5 ft and is 162 ft high, or a building volume of 680 cu ft per 1000 lb steaming capacity per hour. The steam conditions of 275 lb per sq in. pressure and 725 F temperature are the same as those prevailing in the remainder of the plant. The circulation of each half of the boiler unit, with its accompanying proportion of water walls, is independent. The superheater, economizer, and air heater of each half of the unit are also independent. The air-inlet end of the air heaters and similarly the gas-discharge end of the air heaters are connected to a common plenum chamber to eliminate the fan auxiliaries as a source of boiler outage. By this arrangement the unit may develop about 75 per cent of maximum capacity with half of the fan equipment idle. Aside from innovations regarding the twin arrangement, the boiler and furnace are of conservative design. Heat-release rates, absorption rate per unit of surface, and gas velocities entering the tube bank are moderate. Large boiler drums were provided in order to confine water-level fluctuations within safe limits regardless of the rapidity or range of load changes. The visible range within the water glass accommodates a 13 per cent change in the volume of water contained in the boiler and water walls up to the normal water level. This is equivalent to 4.5 per cent of the hourly output at maximum capacity on the basis of solid water.