Abstract: A friction heater is provided which includes a rotor which rotates relative to a stator to generate heat which is transferred to a wall of a tank which contains a quantity of liquid to be heated. The outer surface of the stator and a surface of the tank are smooth surfaces which are in contact with each other substantially throughout their extent so that virtually no heat is lost at the interface between such surfaces. Baffles are provided in the tank to increase the dwell time of the liquid flowing through the tank.