A Deaerator is a device that is widely used for the removal of oxygen and other dissolved gases from the feed water to steam-generating boilers.

In particular, dissolved oxygen in boiler feed waters will cause serious corrosion damage in steam systems by attaching to the walls of metal piping and other metallic equipment and forming oxides (rust).

Dissolved carbon dioxide combines with water to form carbonic acid that causes further corrosion. Most deaerators are designed to remove oxygen down to levels of 7 ppb by weight (0.005 cm³/L) or less as well as essentially eliminating carbon dioxide.

There are two basic types of deaerators, the tray-type and the spray-type: