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Guide to Air Cleaners in the Home


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.”

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

•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.

•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.
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Understanding the Types of Air Cleaning Devices
Before deciding whether to use an air cleaning device, several questions should be considered:

•What types of pollutants can an air cleaner remove?

•How is the performance of an air cleaner measured?

•Will air cleaning reduce adverse health effects?

•What other factors should I consider?

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

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.

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 gas-phase 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.

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

•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.

•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.

•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 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.

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.

In addition to understanding the different types of air cleaning devices, consumers should consider their
performance, as explained in the next section.

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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 Air-Conditioning Engineers, or 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.

•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.

Filters with a MERV between 7 and 13 are likely to be nearly as effective as true HEPA filters.

•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

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.

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

UVGI cleaners may not reduce allergy or asthma symptoms.

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.

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, or CADR, developed by the Association of
Home Appliance Manufacturers, or 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

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 Website at www.cadr.org .

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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 completely 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

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Additional Factors to Consider
When making decisions about using air cleaning devices, consumers should also consider:

•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.

•Major Costs: These include the initial purchase, maintenance (such as cleaning or replacing filters and
parts), and operation (such as electricity).

•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.

•Soiling of Walls and Other Surfaces: Ion generators generally are not designed to remove the charged
particles that they generate from the air. These charged particles may deposit on room surfaces, soiling
walls and other surfaces.

•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.
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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.
Indoor Air Quality
Indoor air quality is a big concern for a lot of homeowners.  However, most folks out there have
absolutely no idea how to address these concerns and rely on their HVAC contractor to enlighten them.

Problem is, most contractors want to fatten their bank accounts as much as possible, at your expense,
and will try to sell you on all kinds of things you don't really need.  I, on the other hand,  do not make a
commission on what I sell to you so I can give it to you straight.

You do not need an electronic air cleaner or super expensive HEPA filtration system.  These are
expensive and have to be maintained by your contractor at an ongoing expense to you. Can anyone say

I believe, and so does the EPA, that all you really need is a good pleated filter with a MERV value of
around 10 - 14 and possibly the addition of a UV light to kill viruses the filters miss.

Below is a publication put out by the EPA on this subject and a link to their site.  Its a rare thing when the
government and I see eye-to-eye on something but this is one of those times.