Research into heat exchanger network (HEN) retrofit has focused on either complete automation or evolutionary, thermodynamic approaches. The former involves the solution of mixed-integer, nonlinear programs, with the advantage of rigor, but suffering from exorbitant computational overheads. On the other hand, existing thermodynamic approaches, though useful in greenfield design, are inadequate for retrofit problems. Using a visualization tool that makes graphically explicit both the loads and the driving forces in a heat exchanger network-providing a succinct, graphical description of the first and second laws of thermodynamics applied to the system - we present design guidelines which facilitate rapid evolution of good retrofit solutions by inspection. The method is elucidated using case studies, the retrofits proposed are comparable or superior to existing solutions and are more rapidly obtained, and the rationale behind the proposed modifications is easily documented. This final feature greatly enhances the industrial acceptability of the approach.