The heat exchanger is a device in which heat transfer takes place between two fluids at different temperatures. Among various classifications of heat exchangers, parallel and counter flow types are used widely in many industrial applications. This paper presents two fuzzy logic expert systems (FLESs), one for parallel-flow and another for counter-flow double-pipe heat exchanger (DPHE). Such FLESs are capable of predicting the exit temperature of heat carrier fluids and its effectiveness in an accurate manner. In total, 96 sets of experiments have been conducted for parallel and counter flow types under different combinations of the mass flow rate. The performance accuracy of the fuzzy logic expert system is measured by comparing fuzzy predicted results with experimental data sets. Such a comparison indicates a good agreement between experimental data sets and fuzzy predicted results. The accuracy of the parallel-flow FLES in predicting the exit temperature and its effectiveness is 92.78% and 95%, respectively. The accuracy of the counter-flow FLES in predicting the exit temperature and its effectiveness is 94.28% and 95.5%, respectively.