A regenerative heat exchanger, or more commonly a regenerator, is a type of heat exchanger where heat from the hot fluid is intermittently stored in a thermal storage medium before it is transferred to the cold fluid. To accomplish this the hot fluid is brought into contact with the heat storage medium, then the fluid is displaced with the cold fluid, which absorbs the heat.

In regenerative heat exchangers, the fluid on either side of the heat exchanger can be the same fluid. The fluid may go through an external processing step, and then it is flowed back through the heat exchanger in the opposite direction for further processing. Usually the application will use this process cyclically or repetitively.

Regenerative heating was one of the most important technologies developed during the Industrial Revolution when it was used in the hot blast process on blast furnaces. It was later used in glass melting furnaces and steel making, to increase the efficiency of open hearth furnaces, and in high pressure boilers and chemical and other applications, where it continues to be important today.