Abstract: Disclosed is a system and method for control of in-door ventilation in a building having a series of rooms separated by walls. The system includes: at least one air treatment device arranged to treat the air; a plurality of fan units, including a fan and at least one sensor; and a central computing device adapted to collect data from the sensors and control the fans. Each wall is provided with an opening, the fan units are disposed in the openings to provide an air flow transporting air from the first room through the series of rooms to the last room and then back to the first room, and the air treatment device is disposed to treat the air.