A new heat exchanger design procedure is presented. It can be used with any existing state-of-the-art exchanger rating program. Rather than systematically exploring the whole of the available range of exchanger sizes (diameters and tube lengths), it determines the relationships between duty and tube length, pressure drop and tube length, etc. for a range of diameters. This information is then used to clearly indicate the full range of geometries that are suitable for a given duty and given constraints. As the example presented in the paper shows, this can be achieved by undertaking very few rating calculations (typically four to six). Conventional design procedures can involve hundreds of such calculations. The graphical representation provides the designer with clear guidance regarding the influence of allowable pressure drop on required geometry. It can also be used to appraise rapidly the amount of thermal over design introduced through the selection of a specific geometry.