The air leakages through the air ducts of air conditioning and ventilation systems applied to residential, commercial, and industrial buildings cause higher energy consumption costs, less thermal comfort, and worsening of internal air quality. Also, the leakages affect the design parameters of air conditioning and ventilation systems negatively. The purpose of this study is to experimentally determine the suitable torque strength on the bolt coupling in low and middle pressure self-flanged rectangular cross-sectional air ducts to eliminate air leakages through the bolt couplings. The orifice used during the tests to measure the air leakages was established in accordance with ISO 5167-1:2003 and ISO 5167-2:2003. The inner surface of the tested air ducts is 16.25 m(2). In order to figure out the rate of the air leakages in low and middle self-flanged rectangular cross-sectional air ducts, the tests were carried out at the air pressure levels of 100, 300, 500, 700, 900, 1100, 1300, and 1500 Pa with the torque strengths of 6, 8, 10, 12, 14, and 16 N m at each pressure levels with and without G clamps. As a result, the most appropriate torque strength values on the bolt coupling, depending upon air pressures, were determined experimentally in the low and middle pressure air ducts. The minimum air leakages rates are obtained at torque strengths of 8 N m with G clamps.