Installations for lighting, heating, refrigerating, drying, ventilating, including apparatus for conditioning air or other gases by heating, cooling, humidyfying, dehumidifying, heat or moisture exchange and cleaning channels and ducts incorporated in such apparatus, airborne refuse conveying installations. heat exchangers not being parts of machines, warm air furnaces, fans, blowers, ventilators, air grilles, air valves, air dampers, air diffusers, dry or wet filters or separators; electrostatic precipitators. Dryers for lumber, veneer, board sheets, cellulose, and other firbrous materials inlcuding paper, cardboard, grain, flash-dryers