Thermal stratification is a significant performance parameter for thermal energy storage tanks. In present study, the thermal stratification of vertical mantled hot water tank was investigated by placing different obstacle inside the tank. Four different obstacles were placed inside the tank in four different distances from the tank bottom. Thus effects of the obstacle types and positions were investigated. At the end of study, it was found that obstacle placed inside the tank enhanced the thermal stratification. Results were presented in the terms of temperature distribution, energy storing capacity, Richardson Number, consumption outlet and mantle outlet temperature. All these values were improved by placing the obstacle inside the tank, according to ordinary tank. The best thermal stratification was obtained between Y= 200 and Y=300 mm the distance from the tank bottom. A type obstacle supplied the best thermal stratification. (C) 2016 Elsevier Ltd. All rights reserved.