CFBCAD©, an Expert system developed jointly by the authors, is used to investigate into the effect of steam parameters on the size and configuration of circulating fluidized bed (CFB) boilers. Resulting data would assist designers and users to appreciate the influence of steam cycle parameters on the overall design of CFB boilers. The paper studies the effect of different steam cycles ranging from small capacity, low pressure boilers without reheat, to large capacity, high pressure reheat boilers. The drum pressure exerts an important influence on the area as well as the configuration of heating surfaces. The temperature difference between the flue gas and the feed water inlet temperature has an optimum value for minimum heat transfer surface requirement.