Economizers improves the boiler efficiency. It has been found that about 1% efficiency of boiler is increased by increasing temperature of feed water by 6 °C with help of economiser.
It reduces the losses of heat with the flue gases, The temperature of flue gases is about 370°C to 540°C at exit of last super heater or reheater, having large amount of heat energy which otherwise otherwise would have been wasted.
It reduces the consumption of fuel. It has been estimated that about 1% of fuel costs can be saved for every 6 °C rise in temperature of the boiler feed water.
It reduces thermal stresses in the boiler due to reduced temperature differential in the boiler.