Economiser is a device used to heat feed water by utilising the heat in the exhaust flue gases before leaving through the chimney. It improves the economy of the steam boiler.

Following are the advantages of using an economiser.

There is about 15 to 20 % of coal saving.
It increases the steam raising capacity of a boiler because it shortens the time required to convert water into steam.
It prevents formation of scale in boiler water tubes, because the scale formed is the economiser tubes can be cleaned easily.
since the feed water entering the boiler is hot, therefore strains due to unequal expansions are minimised.