Enclosure constructions comprise a housing configured to enclose an upper chamber of reactors, associated showerheads, and material source or gas lines of a semiconductor fabrication assembly. A heating element and fan impeller are inside the housing. A motor is disposed outside of the housing and is operatively coupled to the fan impeller. A controller is used to operate one or both of the heating element and the motor to produce heated air that is distributed within the housing. The heated air distributed in the housing has a uniform temperature, minimizes or eliminates the number of heat zones in the assembly, and heats the material source lines to eliminate the need for heating jackets, associated controllers, and associated insulation. The enclosure construction reduces the complexity and spatial packing density of the assembly to facilitate assembly, installation, and maintenance of the assembly, and improves the operating thermal efficiency of the assembly.