Fouling dominates the design of heat exchangers used in crude oil preheat trains. It also dominates the lifetime cost of the trains, where the most important cost factor is lost profit through reduced production. Thus, the design objective should be the identification of geometries that provide acceptable performance throughout a desired operating period. This paper suggests a new design approach for shell-and-tube heat exchangers in refinery preheat trains that uses dynamic crude oil fouling models rather than conventional fouling factors to yield designs that are capable of achieving a specified operating period between cleaning operations.