The use of TiO2–water nanofluid as a working fluid for enhancing the performance of a flat plate solar collector has been studied. The volume fraction of the nanoparticles was 0.1% and 0.3% respectively, while the mass flow rates of the nanofluid varied from 0.5 to 1.5 kg/min, respectively. Thermo-physical properties and reduced sedimentation for TiO2-nanofluid was obtained using PEG 400 dispersant. The results reveal the impact and importance of each of these parameters. Energy efficiency increased by 76.6% for 0.1% volume fraction and 0.5 kg/min flow rate, whereas the highest exergy efficiency achieved was 16.9% for 0.1% volume fraction and 0.5 kg/min flow rate. Results showed that the pressure drop and pumping power of TiO2 nanofluid was very close to the base fluid for the studied volume fractions.