Maintaining thermal stratification in hot water storage tanks is crucial in the development of thermal energy storage (TES) technology and energy performance. Introducing baffles inside tank helps preserve stratification, since it restricts the mixing in a confined zone. The selection and optimization of baffles are based on their position, number and diameter. Our previous study revealed that the baffle position is a critical parameter, while using multiple baffles has no positive effect on the performance. Therefore, the objective of this study is to conduct a comparative investigation on the effect of the position and diameter of a single baffle on thermal stratification. Three baffle diameters at two different positions are analyzed and compared numerically through a 2D axisymmetric simulation. The results reveal that the baffle position is the key parameter that influences the stratification performance in hot water storage tanks, while baffle diameter has little effect on the tank performance. Moreover, the second case of the second configuration demonstrates better performance, where the hot water volume to tank volume ratio reaches 19.5%.