A Feedwater heater is a power plant component used to pre-heat water delivered to the boiler. Preheating the feedwater reduces the amount of energy needed to make steam and thus reduces plant operation costs. This improves the thermodynamic efficiency of the system, and also helps to avoid thermal shock to the boiler metal when the feedwater is introduced back into the steam cycle.

Feedwater heaters are typically shell and tube heat exchangers where the boiler feedwater passes throught the tubes and is heated by turbine extraction steam and hot drains supplied to the shell side.

Feedwater heaters are used in both fossil- and nuclear-fueled power plants. Smaller versions have also been installed on steam locomotives.