Space Heating and Ventilating Units-Namely, Unit Heaters and Filter Sections, Mixing Box Sections, Combination Filter Sections and Mixing Box Sections, Internal Face and Bypass Sections, External Face and Bypass Sections, Base Sections, Base Sections with Dampers, Return Air Grills, Wall Intake Boxes, Air Discharge Plenums, Humidifiers, Volume Control Dampers, Vibration Isolators and Discharge Air Nozzles