<p>In this paper, the theory for cost optimization of heat exchanger inventory in power cycles is developed for any number of closed and open feedwater heaters (CFH and OFH). For this purpose, endoreversible power cycles are initially analyzed for the following four cases: (i) one CFH with a trap, (ii) one CFH with a mixing chamber, (iii) one CFH before the OFH, and (iv) one CFH after the OFH. Only the most practical scenario of specified power output is studied. The non-dimensional cost function was then generalized, which resulted in the determination of generalized cost optimal equations with respect to the high-side absolute temperature ratio and the fluid temperature ratio along with unit to total cost ratios for all heat exchangers in the system. Based upon these cases, general instructions are provided that can be used to write all relevant cost equations for any number and combination of feedwater heaters in order to remove the need for detailed derivations. A fifth, more complicated, case is studied after this to show the applicability of these guidelines.</p>