This paper is part of the fifth of a series of reports on investigations of heat absorption and distribution of heat transfer in large steam-boiler furnaces, sponsored by the ASME Special Research Committee on Furnace Performance Factors. The furnace heat absorption was determined from the temperature and composition of the furnace exit gases in fifteen tests on a steam generator rated at 165,000 lb per hr of steam at 915 psig and 740 F at the superheater outlet, and which is fired by a spreader stoker on a front-discharge traveling grate. The effect on furnace heat-absorption efficiency is shown for variation of (a) the heat available in the furnace, (b) the excess air, (c) the percentage of combustion air admitted over the fuel bed, and (d) the condition of the furnace walls with respect to ash deposits. Detailed data on the distribution of gas temperature and of excess air in the furnace are presented. The experimental values for the furnace heat-absorption efficiency did not compare favorably with values calculated by either the Stefan-Boltzmann or the Wohlenberg equations. There is evidence, however, that the performance of a spreader-stoker-fired furnace might be predicted by the Wohlenberg equation if it were modified to allow for heat transfer resulting from a combination of suspension and fixed-bed burning.