© 2022 International Solar Energy SocietyThis experimental study aims to determine the effect of the amount of encapsulated phase change material (PCM) on the hot water output in a vertical mantled hot water tank. Paraffin which has a 58–60 °C melting point has been used as PCM, and it has been placed inside the tank with 5-liter cylindrical capsules. First, 4, 8, 12, and 16 paraffin capsules have been placed in the test tank, respectively. While the hot water output has increased with the increasing number of capsules up to 12 capsules, it has decreased dramatically when 16 capsules have been placed in the tank. In order to determine the optimum paraffin amount, 13 and 14 capsules have been placed in the tank, respectively. While 13 capsules have increased the hot water output, 14 capsules have decreased it. At the end of the study, the optimum number of capsules has been observed as 13. Placing 13 paraffin capsules has increased hot water output by 20% than the standard tank. Additionally, the MIX number and Richardson number have indicated that placing paraffin capsules has not been affected the thermal stratification significantly. They have varied approximately ±1.5% in all cases studied.