The efficiency of heat engines is significantly influenced by heat recovery in recuperators. In the case of the Bush-type isobaric expansion engine (IEE), a heat engine which can be operated with heat sources starting from 50°C, the thermal efficiency can be significantly increased by using recuperators. On the other hand, internal fluid volumes of the heat exchanger and the pressure loss arising during operation have a negative effect on the thermal efficiency. Until now, mutual interaction of heat recovery, dead volume and pressure loss has not been studied. In this work a new procedure in which a dynamic heat exchanger model and a thermodynamic approach are combined is proposed and used to identify the limitations of heat recovery in IEEs. As a promising application and an illustrative case study, the utilization of waste heat from a data center as a heat source is considered. For this case, six different working fluids and two different heat exchanger designs are investigated. The IEE can achieve 30% of the Carnot efficiency with working fluid CO₂. Besides, with CO₂, a better engine performance was found for heat exchangers with a smaller cross-section. When operating with working fluid R134a, a high sensitivity to frictional pressure drop was registered.