Three different additive manufactured heat exchangers are experimentally investigated in terms of effectiveness, overall heat transfer coefficient and entropy generation. The heat exchangers are investigated at mass flow rates from 0.0018 − 0.0082 kg/s and at two hot inlet temperatures of 200°C and 400°C. The structure adapted to the flow shows the highest effectiveness and a 80% higher heat transfer coefficient than the less complex additive fin structure, while the pressure drop increases by about 60%. The entropy generation of the optimized structure is the smallest compared to the other ones. The entropy generation of temperature differences is the main contributor, while the losses by friction are only of minor importance. The investigations show that with the possibilities of additive manufacturing, there is still considerable performance potential even in conventional fin structures, which leads to smaller installation space and thus less weight. Furthermore, great attention must be paid to the influence of the manufacturing tolerance as well as the roughness in order to achieve a correct heat exchanger design.