Abstarct: Energy loss recovery in an industrial or building unit provides an attractive opportunity for management of regional energy resources. A large percentage of produced energy in a country is used for domestic and commercial consumption whose significant part is consumed for heating water. This project examines the way to retrieve a part of energy lost in bathhouse and its effectiveness in reducing energy consumption of water heating process by modelling of a vertical Drain Warer Heat Recovery, (DWHR). In DWHR exchanger, warm water from showering passes through a copper pipe after running down the drain and it transfers a part of its thermal energy to cold water flowing through a pipe coiled around the vertical one. In this paper, efficiency of this group of thermal exchangers is estimated exploiting ANSYS FLUENT analytical software. This aim is achieved in two parts, including film thickness measurement in vertical tube using numerical and analytical methods and the thermal modelling of the heat exchanger. Finally, parameters of pressure drop in the coiled pipe, thermal efficiency, heat recovered, as well as NTU are calculated and it is shown that an increase in mass flow rate, decreases the exchanger efficiency. The pressure drop in the coiled pipe in maximum mass flow rate is about 90 kpa which is available according to experimental reports.