How Air Purifiers Work

Cleaning the Air

If ozone generators and ionizing purifiers have questionable efficacy at cleaning air, what can be done to remove contaminants from our homes? There are three basic steps, in order of usefulness:

  1. Get rid of the source of the contaminants. If the problem is cigarette smoke, smoke outside. If mold is causing problems, identify the moldy areas and clean them up. Severe cases may require extensive work to get at mold within walls, but if the mold is left in place, the problem will only get worse. When pet dander is a problem, the pet could be limited to certain areas of the house and kept off furniture. Good hygiene along with regular cleaning and vacuuming will remove a great deal of dust and limit opportunities for mold growth. Using special plastic bags on mattresses and box springs can also keep down allergy-causing contaminants. Image courtesy Andrea Booher/FEMA Mold growing on household walls should be cleaned thoroughly and as soon as possible to avoid illness.
  2. Dilute the air in your house. In other words, open the windows. The air outside probably contains fewer contaminants than what is inside (unless you live downwind from a coal plant). Allowing fresh air inside will sweep away some contaminants.
  3. Clean the air with an effective filter system.

The next logical question, of course, is "how do you know which air cleaners are effective?" Fortunately, there is an industry standard that makes it easy to compare air cleaners. The Association of Home Appliance Manufacturers (AHAM) assigns a Clean Air Delivery Rate (CADR) to air cleaners. AHAM runs a standard test to see how well an air cleaner removes certain contaminants from a volume of air. An air cleaner bearing the AHAM seal will have three CADR numbers listed: one for tobacco smoke, one for pollen and one for dust. A higher number indicates a greater ability to clean air, with maximums of 450 for pollen and smoke and 400 for dust [ref]. AHAM recommends using an air cleaner with a CADR number at least two-thirds the area of the room


From the CADR Web site: "For example, a 10-foot by 12-foot room -- 120 square feet -- would require an air cleaner with a tobacco smoke CADR of at least 80. If your room size is smaller, the unit will simply clean the air more often or faster. If you have ceilings higher than 8 feet, you'll want an air cleaner rated for a larger room."

For lots more information on air cleaners and related topics, check out the links below.


Related Articles

More Great Links


  • "ANSI/AHAM AC-1: Method for Measuting the Performance of Portable Household Electric Room Air Cleaners." Association of Home Appliance Manufacturers.
  • Barrett, Stephen, MD. "Court Dismisses Sharper Image Lawsuit against Consumers Union."
  • "Ozone Generators that are Sold as Air Cleaners: An Assessment of Effectiveness and Health Consequences."Environmental Protection Agency.
  • "Slow adoption takes wind out of air purification sales." DSN Retailing Today, Nov 5, 2001.
  • "Specification for HEPA Filters Used by DOE Contracts." Department of Energy.
  • Weise, Elizabeth. "Ionizing air cleaners get zapped." USAToday, April 4, 2005.
  • "What is AHAM's Clean Air Delivery Rate (CADR)?" Association of Home Appliance Manufacturers.
  • "What is a Cleanroom?" Intel.