Abstract: An improved friction heater with driveshaft that rotates one frictional part relative to another interfitted with it provides, on the driveshaft, screw-and-inertia member to release frictional force between the frictional parts when the frictional parts are being stopped, permitting use of a less powerful drive for start-up and lighter structural support. The interfitted frictional parts are conical in shape and also have automatic-driveshaft release to prevent overheating from wear at the frictional interface after long use. The release provision includes a slot in the lower part of the rotor and a transverse pin in the driveshaft, that engages the slot for normal driving operation. When as result of wear, the relative axial position of rotor and housing changes sufficiently to pass out of the range of normal operation, the slot and pin automatically and correspondingly pass from engagement with each other.