Air Filters

Exposure to pollutants in indoor air has been linked to serious health effects like asthma, respiratory irritation and cancer.

Healthiest Air Filters

  • For a central air system, use a filter rated MERV 10 or higher

  • Clean and replace air filters regularly

  • For portable air filters, choose one with a high-efficiency or HEPA filter

  • Check the California Air Resources Board’s list of certified air cleaners

Do’s & Don’ts

Dirty Details

Inhalation of airborne particles is linked to coughs and respiratory irritation, as well as more serious long-term consequences including lung disease and cancer. Babies, young children, older adults and people with asthma—the very people most likely to spend more time indoors—are most susceptible these health risks.

Though no air filter alone will fully clean the air, you can improve the quality of the air in your home with filters installed in your central heating and cooling system, or with a portable air purifier.

Since large volumes of air circulate through central air systems, a well-maintained central filtration system with a high-efficiency filter may have the greatest impact on indoor air quality.

Central Air Filters

Filters are rated by standards that measure particle removal efficiency—known as the Minimum Efficiency Reporting Value, or MERV. The MERV ratings range from 1 to 20, with higher number ratings removing finer particles at greater efficiencies. Particles smaller than 10 microns—or one-seventh smaller than the width of a human hair – can pass into the lungs when inhaled. Finer particles, 2.5 microns and smaller, can penetrate deep into the lungs.

Central forced air systems are typically fitted with a one-inch-thick panel filter. These basic, flat filters are quite inexpensive, but remove less than 20 percent of particles. These filters are rated MERV 1 to 4, and are not designed to improve indoor air quality. Upgrading to a higher efficiency filter is recommended, since these filters are ineffective at removing contaminants.

Some filters sold online or in stores may have their own rating systems, so you may have to contact the manufacturer.

Medium-Efficiency Filters

Medium-efficiency filters are usually composed of a pleated, woven material and are rated MERV 5 to 8. The pleats create more surface area to trap particles. Some of these filters are washable and reusable, but can become ineffective over time as they can’t be thoroughly cleaned.

Some medium-rated filters also use static electricity generated by the airflow to trap particles. It is important to change this type of filter frequently as the charge may decrease with use.

High-Efficiency Filters

High-efficiency filters remove finer particles in the 1 to 3 micron range. Filters with MERV ratings of 9 to 12 cost more, but are still relatively inexpensive. You should have an HVAC technician inspect your central air system before you upgrade to a filter rated MERV 9 or higher.

Filters rated MERV 13 to 16 are highly efficient and remove very fine particles. They are becoming more common for residential use, but usually can only be installed in central air systems designed or upgraded to accommodate them. Some newer homes are now designed with central air system ductwork to accommodate true HEPA filters, rated MERV 17 and up, which remove 99.97 percent of particles down to 0.3 microns.

If your home does not have a central heating and cooling system with filtration, and you have already taken steps to minimize contaminants, portable air filters are a good option.

Portable Air Filters

These devices remove particles from the air by capturing them in filters or with electrostatic attraction. Some air cleaning devices use ultraviolet lamps to inactivate some airborne pollutants—like viruses, bacteria and mold—but they may not be effective and can be difficult to maintain. As portable filters are designed for single room use, they have a limited capacity to filter air. And according to the EPA, these devices may not be effective at reducing health risks for the most sensitive populations.

Below are our tips for choosing the best portable air cleaner:

  • Check the California Air Resources Board’s list of certified air cleaners.
  • Choose your filter based on the room’s square footage—aim for an air cleaner that can replace a room’s volume of air two to three times per hour.
  • Be wary of ionizing electronic air cleaners. They may intentionally produce ozone, a potent respiratory irritant and the main component of ground-level smog.
  • To avoid ozone, we recommend air cleaners equipped with a high-efficiency or HEPA filter.


  1. American Lung Association, Furnace Filters: Tips About Your Furnace Filter. 2008. Available at
  2. California EPA Air Resources Board, Facts About Reducing Your Exposure to Particle Pollution. 2014. Available at
  3. California EPA Air Resources Board, Reducing Indoor Air Pollution: A Serious Public Health Problem. 2006. Available at
  4. California EPA Air Resources Board, Air Cleaning Devices for the Home: Frequently Asked Questions. 2014. Available at
  5. EPA, Guide to Air Cleaners in the Home. 2008. Available at