This paper shows the application of a graphical design tool originally developed for shell and tube heat exchangers and extended to the case of compact units. Such a graphical tool provides the design space where the available options that meet the heat duty and allowable pressure drops are displayed for the various geometrical parameters. This representation gives the designer the overall view that allows him to reconcile design specifications with the selection of the unit for the given application. The methodology is demonstrated using a design algorithm developed for the case of spiral heat exchangers. Although the design methodology is derived from the concept of full utilization of allowable pressure drop, the design space is determined considering standard exchanger by a set of set of three curves: a curve that represents the heat duty (thermal length) and two curves that represent the pressure drop on the hot and cold streams (exchanger length). The intersection of the two former lines with the heat duty curve that results in a shorter flow length represents the required exchanger dimensions.