On average most air purifier would take 30 minutes to 2 hours to completely cover an entire room. Highly dependent on the fan speed, room size and the air purifier’s purifying coverage, the air purifier first must have the capacity to fullfill the room size. An estimated 300 square feet room size would need an air purifier with at least 300 square feet of purifying coverage. Parallel with the purifying coverage, an air purifier running in 4 speed would take only half of the time covering a room then the same air purifier running in 2 speed. To get the best out of the air purifier, we recommend running the unit at full speed for at least couple of hours and switch back to lower speed to maintain the room quality standard. You should also keep your air purifier running 24 hours a day as dust and other airborne particles circulate throughout the day.