ACH is a way to tell how often the air in their room is circulated. A higher number of air changes presents more opportunities for pollutants to be removed.
For the air cleaner to be able to keep up with unfiltered air entering a room with the suggested room size, the air cleaner must deliver an amount of clean air (CADR) sufficient to deliver clean air in the room 4.84 times per hour.
The ACH calculation is based on an air cleaner’s ability to reduce the concentration of pollutants in a room appropriate for the air cleaner’s size by 80%. The calculation is based on one air change per hour, with a recirculation fan providing complete mixing of air in the room.
If the air cleaner will be used in a room larger than the suggested room size, the number of air changes per hour will be less than 4.8, and the pollutant concentration in the indoor air will be higher. The opposite applies if an air cleaner is used in a room smaller than the suggested room size where the actual air cleanings and circulation per hour will be greater than 4.8. An air cleaner with a higher CADR will be able to remove pollutants from the air at a higher rate than an air cleaner with a lower CADR.
An example of the correlations between ACH and room size
The suggested room size on the packaging gives guidance on how large a room the product is best suited for. The air cleaner works best in a room with closed windows and doors.
The suggested room size for an air cleaner is based upon the CADR obtained for reducing engineered cigarette smoke concentrations. The room size is based upon the ability of the air cleaner to reduce the concentration of smoke particles by 80% in a room to a new steady-state when the air cleaner is operating.
The suggested room size is determined through the following formula: Room Size = (Certified Smoke CADR x 60)/(ACH x 8 Feet Ceiling).
|Personal||Up to 50 ft² (4.7 m²)|
|Small||51 - 99 ft² (4.7 - 9.2 m²)|
|Medium||100 - 155 ft² (9.3 - 14.4 m²)|
|Medium - Large||156 - 210 ft² (14.5 - 19.5 m²)|
|Large||200 - 349 ft² (18.6 - 32.4 m²)|
|Large - Extra Large||350 - 399 ft² (32.5 - 37.1 m²)|
|Extra Large||Over 400 ft² (37.2 m²)|