© 2022 Elsevier LtdThis paper presents the results of a 3D numerical model based on computational fluid dynamics (CFD) simulations to investigate the effect of placing cylindrical encapsulated PCM in a vertical hot water storage tank used in a household solar water heater with a mantle heat exchanger on thermal stratification. To validate the developed CFD model, an experiment was designed, and the numerical model was validated with the results from the experimental study. The influence of adding PCM in the tank on thermal stratification during discharging was analyzed for various parameters such as PCM type, its position, its amount, and its melting temperature. The results showed that the addition of the PCM into a mantled hot water tank increases the thermal stratification and the outlet water temperature in the tank during discharging mode according to without PCM case. In addition, placing the PCM tubes on the top part of the tank results in improvement of 4.98 °C (19.6 %) in the outlet water temperature compared to the case without PCM. It was found that the best thermal stratification was obtained in Case-7, where 56 pieces of PCM tubes filled with salt hydrate were placed at the top of the tank. In this case, the MIX number is 0.130, the Richardson number is 0.0930, and the exergy efficiency is 0.611.