Methodologies for the rapid sizing and costing of heat exchangers have been developed under the aegis of ESDU International plc, London. This paper is a summary of a group of design guides ( referred to as "data items") that cover a wide range of heat exchanger configurations. These data items are aimed at providing rapid selection, sizing, and costing at the process design stage. For two-stream exchangers, the C value method has been adopted in which the costs are expressed per unit (Q/ Delta T-m), where. Q is the heat load and Delta T-m the mean temperature difference. The development and applications of this method are reviewed, with an emphasis on comparisons between various types of exchanger. The nature of variations from the standard cases considered are also discussed. Though the C value method can be applied to two-stream plate-fin exchangers, such exchangers often operate with multiple streams. Approximate calculations for the design of such multistream exchangers can be made using the concept of the volumetric heat transfer coefficient. This methodology can be combined with standard curves of the cost per unit volume as a function of volume to obtain an approximate costing of such exchangers.