Air Cleaners

Guide to

in the Home
Introduction

Indoor air pollutants are unwanted, sometimes harmful 

materials in the air. Indoor air pollution is among the top 

five environmental health risks. Usually the best way to 

address this risk is to control or eliminate the sources of 

pollutants, and to ventilate a home with clean outdoor air. 

The ventilation method may, however, be limited by weather 

conditions or undesirable levels of contaminants contained in 

outdoor air. If these measures are insufficient, an air cleaning 

device may be useful. Air cleaning devices are intended to 

remove pollutants from indoor air. Some air cleaning devices 

are designed to be installed in the ductwork of a home’s 

central heating, ventilating, and air-conditioning (HVAC) 

system to clean the air in the whole house. Portable room 

air cleaners can be used to clean the air in a single room or 

specific areas, but they are not intended for whole-house 

filtration. The following pages will provide information on 

different types of air cleaning devices and how they work.

Please Note: EPA neither certifies 

nor recommends particular 

brands of home air cleaning 

devices. While some home air 

cleaning devices may be useful in 

some circumstances, EPA makes 

no broad endorsement of their 

use, nor specific endorsement 

of any brand or model. This 

document describes performance 

characteristics associated with 

several types of air cleaners sold to 

consumers for home use. It does 

not discuss the effectiveness of air 

cleaners installed in the HVAC 

systems of large buildings, such 

as apartments, offices, schools, or 

public buildings. 

Under Federal pesticide law, 

manufacturers of ozone generators 

must list an EPA establishment 

number on the packaging. This 

number merely identifies the 

facility that manufactured the 

product. Display of this number 

implies neither EPA endorsement 

nor that EPA has found the 

product to be safe or effective. 

Some portable air cleaners sold in 

the consumer market are ENERGY 

STAR® qualified. Please note 

the following disclaimer on their 

packaging: “This product earned 

the ENERGY STAR by meeting 

strict energy efficiency guidelines 

set by EPA. EPA does not endorse 

any manufacturer claims of 

healthier indoor air from the use of 

this product.”
www.epa.gov/iaq 3

What Types of Pollutants Can an 

Air Cleaner Remove? 

There are several types of air cleaning devices available, each 

designed to remove certain types of pollutants. 

Particle Removal

Two types of air cleaning devices can remove particles from the 

air—mechanical air filters and electronic air cleaners. Mechanical 

air filters remove particles by capturing them on filter materials. 

High efficiency particulate air (HEPA) filters are in this category. 

Electronic air cleaners such as electrostatic precipitators use a process 

called electrostatic attraction to trap charged particles. They draw 

air through an ionization section where particles obtain an electrical 

charge. The charged particles then accumulate on a series of flat 

plates called a collector that is oppositely charged. Ion generators, or 

ionizers, disperse charged ions into the air, similar to the electronic 

air cleaners but without a collector. These ions attach to airborne 

particles, giving them a charge so that they attach to nearby surfaces 

such as walls or furniture, or attach to one another and settle faster.

Indoor Air Pollutants

Pollutants that can affect air quality in a home fall into the following categories:

X Particulate matter includes dust, smoke, pollen, animal dander, tobacco smoke, particles generated from combustion 

appliances such as cooking stoves, and particles associated with tiny organisms such as dust mites, molds, bacteria, 

and viruses.

X Gaseous pollutants come from combustion processes. Sources include gas cooking stoves, vehicle exhaust, and tobacco smoke. They also come from building materials, furnishings, and the use of products such as adhesives, paints, 

varnishes, cleaning products, and pesticides.

Understanding the 

Types of Air Cleaning 

Devices

Before deciding whether to use an air 

cleaning device, several questions should 

be considered:

X What types of pollutants can an air 

cleaner remove? 

X How is the performance of an air 

cleaner measured?

X Will air cleaning reduce adverse health 

effects?

X What other factors should I consider?

These questions will be addressed in the 

next few pages. 

Guide to Air Cleaners in the Home
4 www.epa.gov/iaq

Gaseous Pollutant Removal

Gas-phase air filters remove gases and odors by using a material called a sorbent, such as activated carbon, which 

adsorbs the pollutants. These filters are typically intended to remove one or more gaseous pollutants from the airstream 

that passes through them. Because gas-phase filters are specific to one or a limited number of gaseous pollutants, they 

will not reduce concentrations of pollutants for which they were not designed. Some air cleaning devices with gasphase filters may remove a portion of the gaseous pollutants and some of the related hazards, at least on a temporary 

basis. However, none are expected to remove all of the gaseous pollutants present in the air of a typical home. For 

example, carbon monoxide is a dangerous gaseous pollutant that is produced whenever any fuel such as gas, oil, 

kerosene, wood, or charcoal is burned, and it is not readily captured using currently available residential gas-phase 

filtration products.

Pollutant Destruction

Some air cleaners use ultraviolet (UV) light technology intended to destroy pollutants in indoor air. These air cleaners 

are called ultraviolet germicidal irradiation (UVGI) cleaners and photocatalytic oxidation (PCO) cleaners. Ozone 

generators that are sold as air cleaners intentionally produce ozone gas, a lung irritant, to destroy pollutants.

X UVGI cleaners use ultraviolet radiation from UV lamps that may destroy biological pollutants such as viruses, 

bacteria, allergens, and molds that are airborne or growing on HVAC surfaces (e.g., found on cooling coils, drain 

pans, or ductwork). If used, they should be applied with, but not as a replacement for, filtration systems.

X PCO cleaners use a UV lamp along with a substance, called a catalyst, that 

reacts with the light. They are intended to destroy gaseous pollutants by 

converting them into harmless products, but are not designed to remove 

particulate pollutants.

X Ozone generators use UV light or an electrical discharge to intentionally 

produce ozone. Ozone is a lung irritant that can cause adverse health effects. At 

concentrations that do not exceed public health standards, ozone has little effect 

in removing most indoor air contaminants. Thus, ozone generators are not 

always safe and effective in controlling indoor air pollutants. Consumers should 

instead use methods proven to be both safe and effective to reduce pollutant 

Ozone is a 

lung irritant 

that can cause 

adverse health 

effects.

Guide to Air Cleaners in the Home
www.epa.gov/iaq

HVAC

Heating, 

ventilating, and 

air-conditioning

PCO

Photocatalytic 

oxidation

UV

Ultraviolet

UVGI

Ultraviolet 

germicidal 

irradiation

R e m i n d e r s concentrations, which include eliminating or controlling pollutant sources and increasing outdoor air 

ventilation. Visit www.epa.gov/iaq/pubs/ozonegen.html for more information on ozone generators 

sold as air cleaners.

The chart below provides a brief summary of air cleaning technologies and the pollutants they are 

designed to control. 

In addition to understanding the different types of air cleaning devices, consumers should consider 

their performance, as explained in the next section.

AIR CLEANING 

TECHNOLOGIES

POLLUTANTS 

ADDRESSED

LIMITATIONS

Filtration

Air filters Particles Ineffective in removing larger particles because most settle from 

the air quickly and never reach filters.

Gas-phase 

filters

Gases Used much less frequently in homes than particle air filters. The 

lifetime for removing pollutants may be short.

Other Air 

Cleaners

UVGI Biologicals

Bacterial and mold spores tend to be resistant to UV radiation 

and require more light or longer time of exposure, or both, to be 

killed.

PCO Gases

Application for homes is limited because currently available 

catalysts are ineffective in destroying gaseous pollutants from 

indoor air.

Ozone 

generators

Particles, gases, 

biologicals

Sold as air cleaners, they are not always safe and effective in 

removing pollutants. By design they produce ozone, a lung irritant.

5

Guide to Air Cleaners in the Home
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How is the Performance of an Air Cleaner Measured?

There are different ways to measure how well air cleaning devices work, which depend on the type of device and the 

basic configuration. Air cleaning devices are configured either in the ductwork of HVAC systems (i.e., in-duct) or as 

portable air cleaners.

In-duct Particle Removal

Most mechanical air filters are good at capturing larger airborne particles, such as dust, pollen, dust mite and 

cockroach allergens, some molds, and animal dander. However, because these particles settle rather quickly, air filters 

are not very good at removing them completely from indoor areas. Although human activities such as walking and 

vacuuming can stir up particles, most of the larger particles will resettle before an air filter can remove them.

Consumers can select a particle removal air filter by looking at its efficiency in removing airborne particles from the 

air stream that passes through it. This efficiency is measured by the minimum efficiency reporting value (MERV) 

for air filters installed in the ductwork of HVAC systems. The American Society of Heating, Refrigerating and AirConditioning Engineers (ASHRAE) developed this measurement method. MERV ratings (ranging from a low of 1 to 

a high of 20) also allow comparison of air filters made by different companies.

X Flat or panel air filters with a MERV of 1 to 4 are commonly used in residential furnaces and air conditioners. 

For the most part, such filters are used to protect the HVAC equipment from the buildup of unwanted materials 

on the surfaces such as fan motors and heating or cooling coils, and not for direct indoor air quality reasons. They 

have low efficiency on smaller airborne particles and medium efficiency on larger particles, as long as they remain 

airborne and pass through the filter. Some smaller particles found within a house include viruses, bacteria, some 

mold spores, a significant fraction of cat and dog allergens, and a small portion of dust mite allergens. 

Guide to Air Cleaners in the Home
www.epa.gov/iaq

X Pleated or extended surface filters

• Medium efficiency filters with a MERV of 5 to 13 are 

reasonably efficient at removing small to large airborne 

particles. Filters with a MERV between 7 and 13 are likely 

to be nearly as effective as true HEPA filters at controlling 

most airborne indoor particles. Medium efficiency air filters 

are generally less expensive than HEPA filters, and allow 

quieter HVAC fan operation and higher airflow rates than 

HEPA filters since they have less airflow resistance.

• Higher efficiency filters with a MERV of 14 to 16, 

sometimes misidentified as HEPA filters, are similar in 

appearance to true HEPA filters, which have MERV values 

of 17 to 20. True HEPA filters are normally not installed 

in residential HVAC systems; installation of a HEPA filter in an existing HVAC system would 

probably require professional modification of the system. A typical residential air handling unit and 

the associated ductwork would not be able to accommodate such filters because of their physical 

dimensions and increase in airflow resistance. 

Some residential HVAC systems may not have enough fan or motor capacity to accommodate 

higher efficiency filters. Therefore, the HVAC manufacturer’s information should be checked 

prior to upgrading filters to determine whether it is feasible to use more efficient filters. Specially 

built high performance homes may occasionally be equipped with true HEPA filters installed in a 

properly designed HVAC system.

There is no standard measurement for the effectiveness of electronic air cleaners. While they may 

remove small particles, they may be ineffective in removing large particles. Electronic air cleaners can 

produce ozone—a lung irritant. The amount of ozone produced varies among models. Electronic air 

cleaners may also produce ultrafine particles resulting from reaction of ozone with indoor chemicals 

such as those coming from household cleaning products, air fresheners, certain paints, wood flooring, or 

carpets. Ultrafine particles may be linked with adverse health effects in some sensitive populations.

ASHRAE

American Society 

of Heating, 

Refrigerating and 

Air-Conditioning 

Engineers

HEPA

High efficiency 

particulate air

HVAC

Heating, 

ventilating, and 

air-conditioning

MERV

Minimum 

efficiency 

reporting value

R e m i n d e r s

7

Filters with a 

MERV between 7 

and 13 are likely 

to be nearly as 

effective as true 

HEPA filters.

Guide to Air Cleaners in the Home
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In-duct Gaseous Pollutant Removal

Although there is no standard measurement for the effectiveness of gas-phase air filters, ASHRAE is developing a 

standard method to be used in choosing gas-phase filters installed in home HVAC systems. Gas-phase filters are much 

less commonly used in homes than particle air filters. The useful lifetime of gas-phase filters can be short because the 

filter material can quickly become overloaded and may need to be replaced often. There is also concern that, when full, 

these filters may release trapped pollutants back into the air. Finally, a properly designed and built gas-phase filtration 

system would be unlikely to fit in a typical home HVAC system or portable air cleaner.

In-duct Pollutant Destruction

There is no standard measurement for the effectiveness of UVGI cleaners. Typical 

UVGI cleaners used in homes have limited effectiveness in killing bacteria and 

molds. Effective destruction of some viruses and most mold and bacterial spores 

usually requires much higher UV exposure than is provided in a typical home 

unit. Furthermore, dead mold spores can still produce allergic reactions, so UVGI 

cleaners may not be effective in reducing allergy and asthma symptoms.

There is no standard measurement for the effectiveness of PCO cleaners. The 

use of PCO cleaners in homes is limited because currently available catalysts are 

ineffective in destroying gaseous pollutants from indoor air. Some PCO cleaners 

fail to destroy pollutants completely and instead produce new indoor pollutants 

that may cause irritation of the eyes, throat, and nose.

UVGI cleaners 

may not 

reduce allergy 

or asthma 

symptoms.

Guide to Air Cleaners in the Home
www.epa.gov/iaq

R e m i n d e r s

9

Portable Air Cleaners

Portable air cleaners generally contain a fan to circulate the air and use one or more of the air cleaning 

devices discussed above. Portable air cleaners may be moved from room to room and used when 

continuous and localized air cleaning is needed. They may be an option if a home is not equipped with a 

central HVAC system or forced air heating system. 

Portable air cleaners can be evaluated by their effectiveness in reducing airborne pollutants. This 

effectiveness is measured by the clean air delivery rate (CADR) developed by the Association of Home 

Appliance Manufacturers (AHAM). The CADR is a measure of a portable air cleaner’s delivery of 

contaminant-free air, expressed in cubic feet per minute. For example, if an air cleaner has a CADR of 

250 for dust particles, it may reduce dust particle levels to the same concentration as would be achieved 

by adding 250 cubic feet of clean air each minute. While a portable air cleaner may not achieve its rated 

CADR under all circumstances, the CADR value does allow comparison across different portable air 

cleaners.

Many of the portable air cleaners tested by AHAM have moderate to large CADR ratings for small 

particles. However, for typical room sizes, most portable air cleaners currently on the market do not have 

high enough CADR values to effectively remove large particles such as pollen, dust mite, and cockroach 

allergens. Some portable air cleaners using electronic air cleaners might produce ozone, which is a lung 

irritant. AHAM has a portable air cleaner certification program, and provides a complete listing of all 

certified cleaners with their CADR values on its Web site at www.cadr.org.

AHAM

Association of 

Home Appliance 

Manufacturers 

CADR

Clean air delivery 

rate

ASHRAE

American Society 

of Heating, 

Refrigerating and 

Air-Conditioning 

Engineers

HVAC

Heating, 

ventilating, and 

air-conditioning

PCO

Photocatalytic 

oxidation

UV

Ultraviolet

UVGI

Ultraviolet 

germicidal 

irradiation

Guide to Air Cleaners in the Home
www.epa.gov/iaq

PCO

Photocatalytic 

oxidation

UVGI

Ultraviolet 

germicidal 

irradiation

R e m i n d e r s

Additional Factors to Consider

When making decisions about using air cleaning devices, consumers should also consider:

X Installation: In-duct air cleaning devices have certain installation requirements that must be met, such 

as sufficient access for inspection during use, repairs, or maintenance.

X Major Costs: These include the initial purchase, maintenance (such as cleaning or replacing filters and 

parts), and operation (such as electricity).

X Odors: Air cleaning devices designed for particle removal are incapable of controlling gases and some 

odors. The odor and many of the carcinogenic gas-phase pollutants from tobacco smoke will still 

remain.

X Soiling of Walls and Other Surfaces: Ion generators generally are not designed to remove the charged 

particles that they generate from the air. These particles may deposit on room surfaces, soiling walls 

and other surfaces.

X Noise: Noise may be a problem with portable air cleaners containing a fan. Portable air cleaners 

without a fan are typically much less effective than units with a fan.

Will Air Cleaning Reduce Adverse Health Effects?

The ability to remove particles, including microorganisms, is not, in itself, an indication of the ability 

of an air cleaning device to reduce adverse health effects from indoor pollutants. The use of air cleaning 

devices may help to reduce levels of smaller airborne allergens or particles. However, air cleaners may not 

reduce adverse health effects in sensitive population such as children, the elderly, and people with asthma 

and allergies. For example, the evidence is weak that air cleaning devices are effective in reducing asthma 

symptoms associated with small particles that remain in the air, such as those from some airborne cat 

dander and dust mite allergens. Larger particles, which may contain allergens, settle rapidly before they 

can be removed by filtration, so effective allergen control measures require washing sheets weekly, frequent 

vacuuming of carpets and furniture, and dusting and cleaning of hard surfaces. (For more on allergen 

control, visit www.epa.gov/asthma.) There are no studies to date linking gas-phase filtration, UVGI, and 

PCO systems in homes to reduced health symptoms in sensitive populations.

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Guide to Air Cleaners in the Home
www.epa.gov/iaq

Additional Information

More in-depth analysis of air cleaners is available in the EPA technical document Residential Air Cleaners: 

A Summary of Available Information (Second Edition), EPA 402-F-08-005, May 2008. 

Web site: www.epa.gov/iaq/pubs/residair.html

An electronic copy of this brochure, EPA 402-F-08-004, is available at www.epa.gov/iaq/pdfs/aircleaners.pdf

For additional hard copies of this brochure and other EPA indoor air publications, contact: 

National Service Center for Environmental Publications (NSCEP)

P.O. Box 42419

Cincinnati, OH 42419

phone: (800) 490-9198

fax: (301) 604-3408

Web site: www.epa.gov/nscep

Conclusion

Indoor air pollution is among the top five environmental health risks. The best way to address this risk is to control 

or eliminate the sources of pollutants, and to ventilate a home with clean outdoor air. The ventilation method may, 

however, be limited by weather conditions or undesirable levels of contaminants in outdoor air. If these measures are 

insufficient, an air cleaning device may be useful. While air cleaning devices may help to control the levels of airborne 

allergens, particles, or, in some cases, gaseous pollutants in a home, they may not decrease adverse health effects from 

indoor air pollutants.

Guide to Air Cleaners in the Home
Office of Air and Radiation

Indoor Environments Division

(6609J)

EPA - 402-F-08-004

May 2008