An air cleaner's effectiveness is measured by how thoroughly it captures particles and the amount of air it can process in a given period of time. It's only as good as its ability to catch particles of all sizes and process enough air to make a difference.
The effectiveness of a filter is tested and given ASHRAE (American Society of Heating, Refrigeration and Air-conditioning Engineers) ratings. The first rating, Initial Staining Dirt Efficiency, is a critical measurement of how well the filter removes microscopic staining particles such as tobacco tar, allergens and grease. The second rating, Average Arrestance Test, refers to the percentage of ordinary dust, hair, lint and other large-particulate matter removed. When comparing ratings, it's important to know which of these two is being listed.
The Association of Home Appliance Manufacturers (AHAM) certifies some portable air cleaners with a Clean Air Delivery Rate (CADR). This measures how many cubic feet per minute (CFM) of air is cleared of a certain size particle. Three particle sizes are rated: smoke (minute), dust (medium) and pollen (large). The higher the CADR rating, the less time the unit needs to remove a given quantity of certain particles from a specified room size. AHAM-certified models are marked with CADR data.
