Ventilating, Heating, Cooling and Air Conditioning Systems Comprising Radiators, Solar Collectors, Central Gas and Electric Heaters, Piping, Regulators and Controls Sold as a Unit; Heat Recovery Units Comprising Thyristors, Cooker Hoods, Roof Fittings, Ventilation Ducts, Supply and Exhaust Air Terminals, Piping, Sleeve Couplings, Fasteners and Insulation Mats Sold as a Unit; Air Conditioning Units; Ventilation Fans