Abstract: A heater unit 1 has a plurality of flat heaters 11 adjacently arranged side by side and having common upper and lower surfaces. The thickness T of the heaters 11 is substantially uniform. Each heater 11 has an adjacent end surface 111 which faces toward an adjacent end surface 111 of the adjacent heater 11. The heater unit 1 also has upper and lower electrodes 21 holding the heaters 11 and respectively attached to the upper and lower surfaces of the heaters 11. The adjacent end surfaces 111 of the heaters 11 adjoining each other, and the upper and lower electrodes 21 form an air gap 12 therebetween. The creepage distance L along each adjacent end surface 111 is larger than the thickness T of the heaters 11. The dielectric strength of the heater unit 1 depends on the creepage distance L. The thickness T of the heaters 11 can be decreased without decreasing the dielectric strength of the heater unit 1. The output of the heater unit 1 increases when the thickness T is decreased.

Abstract: A positive-temperature-coefficient thermistor heating device including of a PTC element, a first electrode formed on its surface, a heat radiating means having heat radiating fins and a second electrode, and conductive particles contained in the first electrode and electrically conductive with the second electrode, and, also, a process for production of a positive-temperature-coefficient thermistor heating device including the steps of printing an electrode material paste containing conductive particles on the surface of a PTC element, heating this to bake it on and form a first electrode having a rough surface, and bringing the first electrode and the second electrode of the heat radiating means into contact by the conductive particles.

Abstract: A heating device for heating air-fuel mixture to be fed to an internal combustion engine has a PTC heat generator having a flat ring-like form with a portion of the inner peripheral surface thereof directly exposed to the passage for the mixture. The heating device also has a heat radiating member having an inner peripheral heat radiating surface confronting the mixture passage and jointed to the PTC heat generator in heat conducting relation therewith.