Adequate ventilation is important because it protects both our health and home. However, the ventilation and energy requirements necessary to achieve good indoor air quality (IAQ) may interfere with one another. This paper presents the energy-saving potential of a ventilation system with an air-cleaning unit and demand control in a multi-residential building. This strategy is based on the demand to save energy in ventilation by reducing the supply of outdoor air using air cleaning while maintaining the desired air quality. Hence, the operation mode of the ventilation system in this study senses the indoor CO2 and HCHO concentrations according to the IAQ code for homes in Korea. The ventilation and air-cleaning modes are then operated independently or simultaneously to optimize the energy usage for ventilation. The simulation results indicate that, in maintaining the required IAQ level, the proposed ventilation system reduces the operation rate of the induction of outdoor air for slightly less than 50% of the operating time and decreases the energy use by approximately 20% with its air-cleaning and demand control mode compared to the conventional systems that employ a continuous ventilation mode. (C) 2015 Elsevier B.V. All rights reserved.