Abstract A methodology has been developed to determine optimal stacking pattern of multi-stream plate-fin heat exchangers using a genetic algorithm. This investigation tries to find out the stacking pattern, which gives the maximum heat load for a given number of fluid streams with some specified properties, mass flow rate and entry temperature. The method of area splitting and successive partitioning has been used for the estimation of heat load. Several direct and indirect checks have been made to test the optimality of the stacking pattern. These include exhaustive search, checking the pattern of cumulative heat load and plate temperature profile along a plane normal to the exchanger. The solutions obtained through the developed algorithm exhibit excellent conformity to all of these criteria.