392, Electric Resistance Heating Devices, 324 for steam or vapor generator which is a fluid-in-circuit type heater, and subclasses 386+ for a heating device for use in converting a substance from a solid or liquid to a gaseous state (especially subclasses 394+ for evaporation device for substance which is a liquid (e.g., water, etc.)).
(steam or vapor generator; is; a fluid-in-circuit type heater) (a solid or liquid to a gaseous state (especially subclasses 394+ for evaporation device for substance; is e.g.; a liquid)
steam or vapor generator a solid or liquid to a gaseous state (especially subclasses 394+ for evaporation device for substance
is is e.g.
a fluid-in-circuit type heater
a liquid