HEN (heat exchanger network) retrofitting is useful to reduce energy consumption in the existing process industries. In this study, several ERS (exchanger reassignment strategies) for HEN retrofitting are proposed and tested by performing single objective optimization on retrofit problems using IDE (integrated differential evolution). A reassignment strategy which includes practical considerations is also developed and used in MOO (multi-objective optimization) on retrofit problems. Results of application problems show that ERS play an important role in obtaining better solutions, and that MOO provides many optimal solutions for HEN retrofitting to decision makers for choosing one of them for implementation. (C) 2014 Elsevier Ltd. All rights reserved.