The performance of a hybrid ventilation system, composed of a natural supply inlet and mechanical exhaust, was predicted numerically for a South Korean apartment. Analysis was performed using Computational Fluid Dynamics (CFD) for three ventilating flow rates: 30, 60, and 120 m(3)/h. The heating period chosen in this study reflects how residents are usually exposed to poorer indoor environments in winter. An effort was made to create acceptable residential comforts regarding air Current, temperature and CO2 concentration distributions. The results show that ventilating flow rates are identified as an important parameter, not only in residential comfort, but also in energy savings. An ACH of 0.7 or greater seems to be a reasonable value for the permissible minimum ventilation now rate in occupied zones. The results also show that for a ventilating flow rate of 60 m(3)/h, Some acceptable criteria are satisfied and residents achieve comfort. In the 30 and 120 m(3)/h cases, however, residents no longer feel as comfortable with regard to thermal conditions and air Currents. Lastly, when a whole apartment has a flow rate of 180 m(3)/h, and the living room-kitchen region has a flow rate of 120 m(3)/h, energy losses Occur. (C) 2009 Elsevier B.V. All rights reserved.