ELECTRIC FLUID HEATER

An electrical resistor heater unit for the heating of liquids including a heater element of porous resistor material located within a casing serves to obstruct the flow path for constraining fluid therein to diffuse into the element through a first surface thereof. The fluid is heated by the element and leaves through a second surface thereof. A porous heat-conducting electrically insulating member having smaller pores than the heater element is disposed about the body first surface and serves as a flow distributor and a pre-heater for both directing fluid to flow through the element and for gradually raising the temperature of the incoming liquid to the temperature attained by the element, thereby minimizing boiling of the liquid externally of the liquid input surface of the member. The porosity of the insulating member may be varied along its axial length to control the liquid flow rate to obtain substantially uniform diffusion through the heater element. The heater element may be divided into concentrically arranged vaporizing and super heating zones separated by a thermally insulating gas gap.