ACH stands for Air Changes per Hour. This indicates how frequently the air purifier filters or changes all of the air in a given space per hour. For example, an ACH rating of 6 means that all of the air in your room is thoroughly filtered six times per hour.

We recommend an ACH of 5 or 6 for healthy indoor air. For individuals with allergies and asthma, an ACH rating of 6 or 8 is best.