How are air changes per hour (ACH) determined? Last Updated: 16th August 2019 The required air changes per hour (ACH) is determined by the ISO class to be met. In comparison, a conventional HVAC system usually makes two to four air changes per hour, whereas in a cleanroom it can range anywhere from 10 to 250 or even more. Previous FAQ What is cleanroom classification? Back to FAQ Next FAQ How many air changes per hour are required for the different cleanroom classifications?
