Heat exchanger networks (HENs) design for optimum minimum approach temperature (DeltaT(min,opt)) is presented using economic and environmental evaluations. The environmental assessment methodology includes seven environmental indices, based on the life-cycle impact assessment (LCIA) of both pre-manufacturing and manufacturing stages for equipment, fuel, and energy. A single normalized and weighted environmental index (I-PC) is developed and then incorporated with the economic index using the analytic hierarchy process (AHP) method to identify DeltaT(min,opt). Three case studies of pinched problems are presented. It is found that DeltaT(min,opt) using I-PC as the objective is similar but not identical to DeltaT(min,opt) using annualized cost as the objective. For some environmental categories, pre-manufacturing impacts are dominant, however, environmental impacts of the HEN are always less than without a HEN. A sensitivity analysis shows the effect of several parameters on DeltaT(min,opt). (C) 2003 Elsevier Science Ltd. All rights reserved.