The aim of this work is to optimize gamma Stirling engine performances with a special care given to the heater. This latter consists of 20 tubes in order to increase the exchange area between the working gas and the hot source. Different parameters were chosen to evaluate numerically and experimentally the heater. The selected four independent parameters are: heating temperature (300-500 degrees C), initial filling pressure (3-8 bar), cooling water flow rate (0.2-3 l/min) and frequency (2-7 Hz). The amount of energy exchanged in the heater is significantly influenced by the frequency and heating temperature but it is slightly enhanced with the increase in the cooling water flow rate. The thermal and the exergy efficiencies of the heater are very sensible to the temperature and pressure variations. (C) 2015 Elsevier Ltd. All rights reserved.