(under subclass 497) Subject matter wherein the heater includes parts or elements to form an outer, protective covering applied over the heating element.
SEE OR SEARCH CLASS
165, Heat Exchange,
177+, for tubular structure.
219, Electric Heating,
437, for immersible heating unit attaching or support means; subclasses 520+ for heat-unit housing, casing or support means; subclass 534 for rigid tubular housing, casing or support; subclass 544 for element embedded within or completely surrounded by core, sheath or support means; and subclass 548 for particular construction or material of core, sheath or support.
