Installations for lighting, heating, refrigerating, drying, ventilating, to wit: apparatus for conditioning air or other gases by heating, cooling, humidifying, dehumidifying, heat - or moistures exchange, cleaning as well as channels and ducts enclosed to such apparatus; airborne refuse conveying installations. Heat exchangers, warm air furnaces, fans, blowers, ventilators, air grilles, air valves, air dampers, air diffusers, dry or wet filters or separators; electrostatic precitators. Dryers for lumber, veneer, board sheets, cellulose, and other fibrous materials, paper, card board, grain, flash-dryers