What does ACH stand for?

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 7 means that all of the air in your room is thoroughly filtered seven times per hour. ACH rating of 5 or 6 is recommended for healthy indoor air.
For individuals with allergies and asthma, an ACH rating of 6 or 8 is best.