CADR is used for portable air cleaners and indicates the amount of relatively clean air that a portable air cleaner can deliver per minute. MERV rating is used for air filters and indicates how efficient the filter is—in other words, the percentage of contaminants it can remove as air passes through it. Unlike CADR, MERV rating does not indicate how much clean air the system can actually deliver, because this will depend on the HVAC system's airflow.