this invention relates to an apparatus for effecting the uniform pre - heating of thermoplastic parisons of the type that are introduced into a blow molding machine for fabrication into a blow molded article . the invention provides a hopper which is intermittently supplied with batches of parisons and through which the parisons move by gravity . a convection heating zone is provided in the hopper to uniformly heat each parison passing therethrough , and a temperature equalization zone is provided adjacent to the heating zone . the parisons are removed from the temperature equalization zone by a continuously moving parison conveyor which forms part of the temperature equalization zone .