In 1939, a fifth steam generating unit was added to the Virginia Polytechnic Institute Central Heating and Power Plant. This unit was an E. Keeler, 500 horsepower, three drum, bent water tube type boiler, fired by a Westinghouse five retort underfeed stoker with link-grate section. Soon after the installation of this unit, W.F. Diamond and C.F. DeBush made an investigation to determine the effects of various fuel bed depths on the efficiency of the unity. Approximately 6 1/2 years have elapsed since their investigation was completed. No other tests have been conducted on the unit up to now. Consequently, its performance characteristics and maximum thermal efficiency at the present time are not accurately known. Even though Diamond and DeBusk made their investigation to determine the effect of various depths of fuel bed on the performance of the unit, the optimum percentage C0₂, and the range of load for maximum thermal efficiency, there is at the present time, a decided difference of opinion among the power plant personnel regarding these facts. It is contemplated that a sixth unit will shortly be installed in the V.P.I. Power Plant. Therefore, it is necessary to know what maximum continuous load and what peak loads for short periods of time the No. five until can be expected to carry now that it has been in operation for almost seven years. During the past two or three years, the operation of the stoker on the No. five unit has not been satisfactory. Large coke trees (see Discussion of Results, page 67) are formed in the fuel bed at the front end of the stoker where coal enters the furnace. There coke trees ride on the fuel bed as it moves from the front end of the furnace to the ash discharge orifice (see Fig 18), and are only partially consumed during combustion. When they reach the ash discharge orifice clogging results. This necessitates cleaning the orifice and ash discharge plates with a firing iron. Actual cases have been known to occur when a complete loss of load and a 50 per cent reduction in steam pressure have resulted from the clogging of the orifice. / Master of Science