Deaeration is the process of removing the dissolved oxygen from the boiler feedwater. Additionally, in the deaeration process, the CO2 is also removed. Removal of these two gases is important in boiler feed water as both of the gases promote corrosion in the boiler or steam system.

An additional benefit of a deaerator is the high water feeding temperature to the boiler, so the risk of low-temperature corrosion on the smoke side is decreased and thermal shocks are eliminated in the boiler.