Global climate change as an implication of global warming causes many physical changes that occur on the surface of the sea, one of which is the temperature of the rising sea water. The condenser is a major part of a Combine Cycle Power Plant (CCPP) system that serves to condense vapor or change the vapor phase after the expansion of the steam turbine into a liquid phase by transferring heat from the vapor into the cooling water medium, ie seawater. Theoretically, the temperature of seawater flowing in the cooling water circulation system has a significant effect on the heat transfer process in the condenser. Increased sea water temperatures will have an impact on decreasing the effectiveness of heat transfer occurring in the condenser so that a suitable coolant flow rate is required to restore the value of heat transfer effectiveness in the condenser. Therefore, it is necessary to analyze the effectiveness calculations that occur between the heat transfer based on the desired design targets of the manufacturer with the actual maximum heat transfer that the condenser may reach. The method used is to perform various calculations, ie calculation of coolant fluid convection coefficient by using Dittus-Boelter heat transfer correlation (forced convection), calculation of heat fluid convection coefficient by Log Mean Temperature Difference (LMTD) method, and calculation on effectiveness heat exchanger with effectiveness method - Number of Thermal Unit. The result of calculation and comparison of actual heat transfer effectivity value with the target of baseline condenser design in PLTGU Grati block 1 showed a decrease of heat transfer effectivity value from 78,15 [%] to 70,76 [%] which happened due to rising sea water temperature. Therefore, to maintain the value of heat transfer effectiveness so as not to decrease, a large open valve outlet condenser opening arrangement was performed to accelerate the flow rate of cooling water in each LMTD with the percentage of outlet valve openings between 46 [%] to 55 [%] so that the heat release in the refrigerant pipe occurs faster.