Air Cleaning

Air cleaning and filtration reduces airborne pollutants.

The best way to improve your indoor air is to first remove or reduce the sources of pollutants – referred to as source control - and secondly, to ventilate with outdoor air. In addition, air cleaning or filtration can help to reduce pollutants already present in the air, but they cannot eliminate them. Air cleaning is not an effective substitute for source control or ventilation.

Types of Air Cleaners

There are two types of air cleaners: portable air cleaners and HVAC (heating, ventilation, and air conditioning) systems.

HVAC Systems

Properly maintaining your HVAC or central air system and upgrading your HVAC filters can improve your home’s air quality. HVAC filters clean pollutants from the air as it passes through them before circulating the air throughout the home or building. Duct-mounted air cleaners can be installed into a central HVAC system to provide filtered air to the home. HVAC systems and duct-mounted air cleaners only filter the air when the system’s fan is running.

HVAC systems usually accommodate a rectangular, one-inch-thick filter that is located in the return ducts – either at the base of the air handling unit or upstream in return grilles. The default filter for these systems is typically of low-efficiency and are rated around a MERV 8. Upgrading your furnace filter with a higher MERV rating, preferably 13 or above, will capture more, smaller particles from the air. These disposable filters cost about $12 each. Filters should be changed about every two months or when the filters are dirty. You can tell if they are dirty by comparing the filter to a white sheet of paper.

Larger buildings can have complex HVAC systems and may need to follow technical guidelines which are best interpreted by certified HVAC professionals.

Portable Air Cleaners

Portable air cleaners, sometimes called air purifiers, remove particulate matter and other airborne pollutants from the air we breathe indoors. Studies show modest health improvements in individuals who consistently use mechanical, portable air cleaners in their home. Units with HEPA-rated filters are the most effective types of air cleaners.

Portable units are best for single room use, rather than multiple room or whole house uses. Large areas and homes may need more than one air cleaner.

Air cleaners should be placed in the room(s) where the most vulnerable occupants spend most of their time - this could be in the living room or an office during the day and in the bedroom at night. Close doors and windows in the room where the air cleaning is running to increase its effectiveness.

If you have very sensitive individuals in your home or odors that are difficult to remove, you may want to consider adding a charcoal filter. Activated charcoal filters (carbon) trap or destroy gaseous pollutants. The charcoal filter may need to be replaced often.

When selecting an air cleaner for your home, select a model that:

  1. Is appropriate for the size of your room.
  2. Has low-cost replacement filters.
  3. Has a HEPA filter.
  4. Has a high CADR (Clean Air Delivery Rate). The CADR should be at least two-thirds of the cubic feet per minute metric (CFM). in other words, if an air purifier's CFM is 200 make sure the CADR is at least 133. 
  5. Is certified by the California Air Resources Board. 
  6. Does not include ultraviolet radiation, disinfection features, ionizers and does not produce ozone. These features can harm health.

Both central and portable air cleaners continue to incorporate newer types of technologies to remove particles, gases and chemical vapors from the air. Newer technologies should be used only after careful consideration, as some may have potentially adverse health consequences, including ozone production or the generation of unintentional pollutants. Many of these newer technologies are still being studied and their effectiveness is unknown. There are no standards for testing these new technologies in the U.S. Testing is also very difficult and expensive, and testing in the laboratory often yields different results than found in the “real world.”

DIY Air Cleaners

If you are unable to purchase a commercial portable air cleaner, do-it-yourself air cleaners are effective and can be made with supplies and material you may already have.

What do I need?
  • 1 box fan (manufactured in 2012 or more recent)
  • 1 20"x 20" furnace filter with a MERV rating of 13 or higher
  • Tape, clamps or bungie cords


Your DIY air cleaner can be used for localized air filtration so you can move it from room to room. The filter on your DIY air cleaner should be changed when dirty, approximately every 6 months or more frequently during a wildfire smoke event.

Are DIY air cleaners safe?

The Environmental Protection Agency (EPA) has tested several DIY air cleaners to confirm that fans are safe to use and will not overheat during use. The following precautions are recommended:

  • Use a newer model fan, 2012 or more recent.
  • Use fans that are labeled with UL (Universal Laboratories) or ELT (Intertek's Electrical Testing Labs).
  • Follow the manufacturer’s instructions.
  • Do not leave children unattended while the fan is in use.
  • Do not use when you are not home.
  • Do not use an extension cord, or a damaged or malfunctioning fan.
  • Keep extra filters on hand, especially during heavy air pollution events such as a wildfire.

More Information:

Page last updated: November 20, 2023

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