Filter Facts: How Air Cleaners Help



Woman and young girl in kitchen with cookies and coffee smilingBy Laurie Ross 

Wondering what air cleaners are all about – and if one will help your family breathe easier at home?

Healthcare professionals often recommend them and manufacturers cite scientific data that proves their systems remove pollutants from the air – but the U.S. Environmental Protection Agency (EPA) cautions there’s no real proof they actually improve health. At the same time, some Allergy & Asthma Network members suggest anything that gives them even the slightest help in reducing symptoms is worth having.

Air cleaners should play just one part of an overall strategy to reduce allergens and irritants in your home.

For airborne allergens, such as pollen, mold, pet dander and dust:

HEPA (high efficiency particulate air) filters remove the majority of airborne allergens and are the standard recommended by allergists.

ULPA (ultra low penetration air) filters remove smaller, ultrafine particles, but EPA cautions they may also reduce air flow.

Electronic air cleaners don’t use filters. Instead, they put out charged ions that attach to airborne allergens or dust, creating statically charged particles that then stick to collecting plates in the air cleaner (electrostatic precipitators) or to walls, floors and furniture (ion generators). Some electronic cleaners emit ozone, a powerful lung irritant.

For smoke, gases and odors:

Gas-phase filters such as activated carbon remove odors and gases, including some elements of tobacco and wood smoke, chemicals and fumes. Look for units with high concentrations of carbon or other materials. EPA cautions that tobacco smoke is made up of more than 400 different particles and toxins, only a few of which can be removed with air cleaners.

For bacteria, viruses and mold:

UVGI (ultraviolet germicidal irradiation) lamps use UV radiation to kill viruses, bacteria and mold spores. EPA cautions that dead mold spores can still trigger allergies and typical home units may not have strong enough UV exposures to effectively kill germs.

Comparing Claims

  • Look for units with sealed compartments that do not allow captured pollutants to escape back into the air.
  • Match the air cleaner to your room size. Figure square footage (multiply length times width); add extra if your room has very high ceilings. A unit built for a large room may clean your smaller one more efficiently, replacing the air more quickly. For maximum efficiency, keep doors and windows closed when running the unit and place unit away from walls and furniture that would restrict airflow.
  • Multiple filters do not mean greater efficiency if they restrict airflow and decrease the amount of air processed.
  • Air cleaners become less effective as filters fill up; when considering a unit, check how frequently filters need to be replaced and how much they will cost.
  • CADR, or clean air delivery rate, is a standard developed by the Association of Home Appliance Manufacturers that measures performance of room air cleaners against tobacco smoke, pollen and dust. CADR is determined by lab tests in ideal conditions; real-life results will be affected by how tightly sealed the room is, how dirty the air is, how much activity there is in the room, how full the filter is, and the amount of time it takes an air purifier to cycle all the air in a room.

Learn more about air cleaners – visit EPA’s Indoor Air Quality page.

Defining Terms

Activated Carbon/Charcoal/Zeolite Filters – adsorb odors and gases and neutralize smoke, chemicals and fumes. Quality varies considerably.

Antibacterial and germicidal filter – treated with agents to kill airborne microorganisms.

Electrostatic precipitators – work like ion generators, but capture impurities within the unit on a collector plate that can be cleaned. The efficiency of the unit reduces as the plate becomes full of particles – especially with tobacco smoke. Some produce ozone, a known airway irritant. 

HEPA filters – High Efficiency Particulate Air filters remove at least 99.97% of particles as small as 0.3 microns, which includes pollen, animal dander, mold spores and dust; they do not capture ultrafine particles like viruses or odors/VOCs/chemical fumes.

Ion generators – emit charged particles (ions) into the air, where they combine with impurities (like dust), then either fall to the floor or stick to walls or furniture. They stick to a surface the way static electricity can make a sock cling to a shirt. Some emit ozone.

Ozone generators – EPA says ozone is a potent lung irritant. Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation.

PCO – photocatalytic oxidation destroys gaseous pollutants and odors, a new technology only recently included in portable units. EPA says the usefulness of PCO cleaners in homes is limited because available photocatalysts are ineffective in completely destroying gaseous pollutants in indoor air.

Pre-filters – remove large particles like pet hair before finer filtration and are important to protect other filters from premature clogging. Change frequently.

ULPA filters – Ultra Low Penetration Air filters remove 99.999% of particles as small as 0.12 microns. This filter density can restrict air flow, resulting in fewer air changes per hour in a given room.

UVGI – Ultraviolet Germicidal Irradiation lamp kills germs. Often used in sterile environments like hospitals, kitchens and labs. EPA says these don’t work efficiently in home units, as the amount of UV required to kill bacteria is quite high. Some units say their UV elements kill mold; but for people with mold allergy, live or dead mold spores can irritate airways and set off allergy symptoms.