The most important problem of heating and cooling systems is the removal of heat from the system. Heat exchangers are the most critical equipment of such systems. However, the use of nanofluids has increased significantly in recent years due to the design limitation of heat exchangers. In this study, the effect of using different nanofluids on the heat transfer performance of a heat exchanger was numerically investigated. A 3D heat exchanger model was created and the thermal performance of the system was analyzed by using different types of fluids at different fluid velocities. Analyzes were performed using the ANSYS Fluent program. According to the results obtained, the highest heat transfer increase was obtained in MgO-TiO2 nanofluid with 33.4% at 0.05 m/s compared to water. The highest and lowest heat transfer rates were calculated with 202.73 W for MgO-TiO2 nanofluid and 121.59 W for PGW (propylene glycol-water mixture) fluid, respectively.