In this paper, we analysed the relation between heat transfer rate and entropy generation for single pressure and dual pressure waste heat recovery boiler. The entropy generation per heat transfer is less in dual pressure boilers than in single pressure boilers because the temperature difference of heat transfer is less in dual pressure boilers than single pressure boilers. The analyses show that bigger boilers (dual pressure) are both more efficient for heat transfer and have less entropy generation per heat transfer. We will show which part of the boiler is the entropy generation occurs and the allocation to each of part of the boiler according to entropy generation. Each type of boiler consists of a preheater, an evaporator and superheater. The source of the hot gas’ is a marine diesel engine and it is exhausted through the ambient. Besides, we propose a new algorithm to calculate the pinch points.