The efficiency of the boiler in a thermal power station is greatly depending on the utilization of waste heat in the flue gas by air preheater and economizer. The increasing in the efficiency of the boiler can be achieved by increasing the performance of air preheater and economizer. Enhancing heat transfer rate by changing the profile of air preheater will lead to increasing the performance of the air preheater and economizer. The changing profile and increasing heat transfer area will increase the heat transfer rate. In 210MW Mettur thermal power station notched flat profile is used as heat transfer area in air preheater segment. In order to improve heat transfer rate, the notched flat profile is replaced by double undulated profile and single seal are replaced by the double seal. Hence heat loss in the air preheater is minimized. The performance of economizer is enhanced by increasing the diameter of the coils. Hence the economizer and air preheater absorb additional heat from exhaust flue gas. The changed profile in air preheater and increased diameter in economizer were analyzed by using ANSYS fluent software. Based on the results the percentage of efficiency in air preheater and economizer is significantly increased.