The present study aimed to determine the impact of a gradual and lineal increase of the air duct leakage factor on various indoor air stability parameters in ventilation systems across the following scenarios: 1) air leakage effect on the air pressure and volume; 2) air leakage effect on the indoor air parameters when the ductwork passes through an uninsulated and unheated premise. A galvanized steel air duct was used for the air leakage measurement sessions, and orifices were cut in the duct before each subsequent measurement session, thus, consecutively decreasing the air tightness factor of the duct over the measurement sessions. The results indicated that the ductwork air tightness affects the stability of the air parameters such as air temperature, relative humidity and CO2 concentration, however, up until certain point, the impact was either non-detectable or negligible. The transition in the behavior of the air stability parameters occurred in line with the introduction of orifices 4→5, resulting in perceptible effects on air pressure, volume etc. Although, this factor may be attributed to the errors caused by low instrument sensitivity or by relatively small number and size of the orifices, authors suggest that minor air duct leakage such as presented in this study may result in the disruption of air stability parameters, which in certain instances is critical.