the tank 13 flows through the opened valve 69 the inlet end 25 and the liquid supply channel 23 into the boiler cavity 22 as long as a supply of water exists in the sealed tank 13 a water level l determined by the height of the slots 82 in the skirt 80 will be retained by the open valve 69 within the reservoir 20 formed by the boiler cavity 22 and the liquid supply channel 23 upon energization of the heater coil 36 water within the restricted chamber 40 that has flowed through the orifice 38 into the enclosure 37 is heated to cause evaporation and dispersal thereof because of the restricted and isolated water volume provided by the enclosure 37 in the boiler cavity 22 an extremely efficient evaporation process is obtained the vapor produced in the enclosure 37 rises through the tube 42 the slotted cover 43 and the duct portion 45 of the housing 32 for discharge through the discharge end 46 into the surrounding environment enhancement of the vapor discharge is obtained by energizing the blower 52 which draws air through the entrance passages 54 in the housing 32 for discharge through the exit passage 53 this air draws vapor formed in the boiler cavity 22 through the duct portion for discharge from the discharge end 46 if the supply tank 13 is in place on the base 14 to establish the active closed state of the magnetic switch 61 energization of the heater coil.