ventilation equipment made principally of plastic and/or metal; namely, exhaust air and supply air fans, self-acting thermostatically controlled outdoor-air valves, flop valves, slide valves, screw-down valves, telescopic valves and conduits, back-pressure valves, valve grates, cupboard grates, refrigerator grates, front roll grates, plinth gratings, ventilation ducts, ventilator doors, ventilator louvers, socket ends, multi-plate air filters, condensers, and parts therefor; water storage tanks for heating and ventilation systems; wood frames, structural conduits, outlets, corridors, channels, flues and wall panels, all for the conveyance of air and thermal fluids for central heating and cooling