Abstract: The fluid heater of this invention employs electromagnetic energy (microwaves) to heat the fluid. The magnetron supplies this energy into a base structure which is juxtaposed but separate from the fluid bearing container. The energy is directed towards the fluid container by a stirrer mounted in the base structure, which rotates at a relatively slow rate. The design of the container is such that the fluid flows in a serpentine fashion. Baffles are arranged and positioned to provide this serpentine path. A fan is provided to cool the magnetron. Standard plumbing means and a circulator pump are provided for entry and exit of fluid as well as an aquastat for critical temperature sensing. Drain and pressure controls are also provided.