In this study, a complex unit consisting of air cleaning, total heat recovery ventilation, and humidification units was developed while satisfying the air quality standards for classrooms. To validate the proposed complex unit, an experimental study comparing the existing heat recovery ventilation unit and the complex unit was conducted in two adjacent classrooms of an existing school in Busan. The complex unit was operated in the following modes: (1) total heat exchange ventilation, (2) air cleaning, (3) bypass, and (4) humidification modes. Results confirmed that it was effective in reducing fine dust in total heat exchange ventilation and air cleaning modes. In addition, it was confirmed that the indoor comfortable humidity range was satisfied under the humidification mode during winter, while indoor temperature is maintained under bypass mode. As a result, the proposed complex unit demonstrates satisfactory performance in maintaining a healthy classroom environment.