This paper provides the thermal analysis of fire-tube boilers used in thermal power plants. For simulation purpose, a small-scale prototype of the original fire-tube boiler is designed using Solid Works. The numerical simulation of the designed model is carried out in ANSYS Fluent. The initial section of the paper represents the pressure and temperature variations along the length of the boiler for different water velocities (25 m/s, 30 m/s, 35 m/s and 40 m/s). The later section deals by changing the boiler casing material between steel, brass and stainless steel to study the pressure and temperature variations at constant water velocity of 30 m/s. Based on the results, the best boiler shell material among these three has been identified. The results have been provided in the form of pressure and temperature contours as obtained from the CFD analysis. © IAEME Publication