Abstract: An electric heater, particularly adapted for supplying heat to hazardous areas where the atmosphere in the area contains particles or fumes that are readily ignited. The heater includes one or more heat radiating members, each cast about a sheathed electric heating element. The terminal ends of the heating element extend into a sealed explosion-proof terminal box. The heat radiating members are serially disposed in a tubular casing, and a motor-operated fan blows air through the casing and over the members, the air being heated as it flows over the heat radiating members.Each member is in the form of an annular hub having integral, heat-dissipating fins extending radially thereof. The outer surface of the hub is formed with a contour that is angled or curved in the direction of the air flow, and such contour is constructed and arranged to provide a Venturi effect to draw air from the inner portion of the hub to the outer periphery and thus prevent build-up of excessive heat at the inner portion.

Abstract: Our invention relates to electric heating elements for heating liquid within a tank, and particularly to heating elements for use in domestic commercial water tanks, wherein the element comprises a metal mounting member secured to the wall of the tank and a sheath portion carried by the mounting member and extending through a hole in the tank wall for immersion in the water in the tank. The sheath portion contains a resistance conductor and insulation which electrically insulates the conductor from the sheath, so that water in the tank is heated when the resistance conductor is electrically connected to a source of electrical energy.Our invention provides means for protecting the electric heating element from damage which may otherwise be caused by a sudden surge of high voltage, such as that which may be caused by lightning disturbances in the immediate vicinity.