Abstract: The invention relates to a method and apparatus for controlling the fresh-air, input-air, exhaust-air, waste-air and return-air flows, as well as the air pressure in the input-air duct and the air pressure in the exhaust-air duct, in an air-conditioning system which comprises at least input-air and waste-air flow meters (6, 20), input-air and exhaust-air pressure meters (12, 19), an input-air fan (5) with its air-flow control (13), a waste-air or exhaust-air fan (18) with its air-flow control (14), a fresh-air flow meter (15), a heat recovery exchanger (4), closing and control mechanisms for exhaust air and return air, coupled together as an outlet-air mechanism (10), and closing and control mechanisms for fresh air and fresh-air bypass, coupled together as an intake-air mechanism (3).