The economizer, also known as an economizer in English, is a device installed at the lower part of the boiler's smoke channel to recover the waste heat from the exhaust flue gases. It heats the boiler feedwater into saturated water under the steam drum pressure, absorbing heat from the high-temperature flue gases, thus lowering the exhaust gas temperature, saving energy, and improving efficiency. Hence, it is named the economizer.

Pipe-type economizers are not restricted by pressure and can be used for boiling applications. They are generally made of carbon steel pipes with an outer diameter of 32 to 51 millimeters. Fin and rib shapes are sometimes added to the pipes to enhance heat transfer. The pipe-type economizer consists of parallel bend pipes arranged horizontally (commonly referred to as serpentine pipes).

The economizer is primarily used in industry and is also increasingly popular in agriculture and some related commercial industries.