Abstract: An auxiliary steam superheater designed to be easily added to an existing steam system to boost the steam temperature to approximately 750.degree. F. This superheater comprising a steam coil system enclosed by an insulated casing which defines a central radiant heating chamber with the coil system spaced inwardly from the inner surface of said casing to provide a convection heat passageway. Hot gases from a heat source are introduced through one end of the casing and into the "interior" of said coil system, thus providing radiant heat directly to the inner surface of said coil system and utilizing the "black body" heat transfer principle. An exhaust flue is provided at the top of said casing in close association to the end of the casing where the hot cases are introduced, the gases flowing through the interior of said coil system and out around the coil along said convection heat path before passing out of said chamber through said flue.