A microwave heater is provided and comprises a tank having a plurality of fluid conduits disposed therein and communicating with a fluid inlet and a fluid outlet. Each fluid conduit comprises a plastic tube with an elongated metal core disposed therein to form an annular flow chamber within the tube. The inlet of a fluid transfer system is coupled to the outlet from the tank while a source of relatively cool fluid is connected to the tank inlet. A microwave generator is operatively coupled to the tank to generate microwave energy throughout the tank in order to heat the water and metal cores within the fluid conduits.
