 
Air Cleaners
Furnaces and central air conditioners are
equipped with a panel air filter whose main purpose is to prevent dust and dirt from entering the heating and cooling
equipment and causing it to malfunction. These filters are effective
for removing particles or particulates above 5-10 microns in size.
(There are 25,400 microns to an inch, and it takes 200 microns to
reach across a dot made by a sharp pencil!) Air cleaners remove from
90% to 99% of air-born particles and are effective
in trapping particulates as small as 0.01 microns.
An air
cleaner removes most of the dust and dirt that is circulated through the heating/cooling system.
The average system circulates the air 4-5 times per hour. Whether
you choose a room-type or one that is mounted on your furnace, air
cleaners can only remove particles in the air that pass
through them. Three common types of air cleaners
are:
- HEPA (High efficiency particulate air)
cleaners - must remove 99.97% of all particulates down to
0.3 microns in size, including spores, pollen, and tobacco smoke
particles. They use a high efficiency pleated filtering media to
remove particles, and are typically available only in portable,
room-size models.
- HEPA-type cleaners - remove 99%+ of all
particulates 6.0 microns or larger, including spores, pollen, and
tobacco smoke particles. They are less effective on very small
particles. They also use high efficiency pleated filtering media
to remove particles, and are typically mounted onto the furnace.
- Electronic air cleaners - remove 99%+ of most particulates of all
sizes, including spores, pollen, and tobacco smoke particles. They
use collection plates and ionizing wires to attract electrically
charged particles; however, the plates and wires must be
frequently cleaned to achieve a 99%+ removal rate. Some models
emit ozone - a known lung irritant.
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