The presented studies are devoted for usefulness of Waste Heat Recovery System (WHRS). The main core is developed original optimization method for exhaust boiler (EB) evaluation in dependence on different thermo-technical factors at the condition of fixed boiler dimensions. In a result system of non-linear equations is built up. To achieve the highest output per one equipment volume unit thorough optimization of WHRS is carried at different technical and operational conditions. WHRS for advanced slow speed diesel power plants is separately highlighted due to significantly lowered flue gas potential. Therefore to utilize gas heat as deep as possible another system of non-linear equations is built up based on fixed gas cooling rate in EB. In a result the pressure and other characteristic choice is carried out at various operational and ambient conditions. Here the main task is to get as high output as possible. Due to significance the impact and measurement method for pollution coefficient from gas side is explored.