Guide to Types of Indoor Air Filters, Air Cleaners and Air Purifiers
AIR CLEANER PURIFIER TYPES - CONTENTS: Guide to types of air purifiers or air cleaners used for Improving indoor air quality. Table comparing types of air cleaners and their efficiency in removing different types and sizes of particles: flat air filters, pleated air filters, electrostatic air cleaners, electronic air cleaners, & HEPA air filters. Guide to filters for removing gases from air. Air cleaner & air filter maintenance schedule table
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
Air purifiers and cleaners:
This article explains the types of air cleaners or air purifiers used to improve indoor air quality in homes. We include a table of types of air cleaners and the types of particles they handle, comparing their ability to remove materials from the air, their ease of maintenance, and their operating cost.
Our page top photo shows that even the naked eye can see comparatively large airborne particles indoors. But many indoor contaminants are simply too small to see, or are not particles at all but rather gases or chemicals.
There are three main types of particulate air cleaners on
the market: mechanical filters, electrostatic filters, and ion
generators. In addition, there are filters with adsorbents,
such as activated carbon, that are capable of removing certain
gases (see Table 7-2above) Most filters are available as standalone
units or as add-ons to the home’s HVAC or ventilation
system. Some hybrid systems on the market combine two
or more strategies, such as a filter to remove particles plus
activated carbon to remove odors and organic gases.
Mechanical Filters. These use a matrix of fiberglass or
synthetic fibers and resin to filter particles out of air passing
through. Some are coated with an oil or adhesive to help
trap particles, and others have a static electrical charge.
Some types of mechanical filters can be cleaned, but most
need to be replaced when full.
As mechanical filters clog,
they become more efficient at trapping particles, but airflow
is reduced. They can either work in stand-alone units
or be incorporated into the HVAC or ventilation system.
Flat filters are the standard fiberglass elements found
in furnaces and air handlers. They are designed to
catch large dust particles and have little effect on the
smaller respirable particles that affect health.
Pleated filters, or “extended media” filters, have
smaller pores designed to capture small- and medium-
sized particles. They are pleated like automobile air
filters to provide greater surface area for improved
airflow. Some will fit into a standard furnace filter
slot, but the higher-efficiency types are generally too
thick and require ductwork modifications. For good
performance, they need to be replaced regularly.
Electrostatic filters use a plastic element that is permanently
charged with static electricity or captures an
electric charge from the passing air. They are a little
more effective than a standard furnace filter at capturing
larger particles such as pollen and mold spores,
and can be washed and reused when full.
HEPA stands for “high-efficiency particulate accumulator.”
These filters range from 95% to over 99% efficient
for particles over 0.3 microns, including mold
spores, mites, pet dander, and some viruses. Because
of their high resistance to airflow, HEPA filters typically
require a separate fan and housing.
Replacement HEPA Filter
elements last a year or longer but cost well over $100
versus $10 to $20 for a medium-efficiency pleated
filter. Most have a prefilter to catch large particles
that would prematurely clog the filter. Prefilters need
to be changed regularly.
Electronic (Electrostatic) Air Cleaners
Electronic air cleaners
(EACs) use a series of electrically charged metal plates or
media filters to pull particles out of the air stream. They
are either portable units designed to clean the air in one
or two rooms or central systems connected to the return
ductwork of the HVAC system. EAC systems create little
resistance to airflow but require a separate fan, which
along with the electrical charging device use about 30 to
50 watts of electricity.
Electronic air cleaners are highly efficient at removing
both small and large particles, but require more maintenance
than many homeowners would like. To remain
effective, the filters must be removed regularly and hosed
down in a large sink or tub. Some are designed to fit in a
In charging the particles with high voltage, EACs also
produce small amounts of ozone, which can be an eye or respiratory
irritant at high levels. Most people are not bothered
by the amount produced. If this a concern, however, look for
a unit with an activated carbon filter to remove the ozone.
Negative Ion Generators to Clean Indoor Air
These work by releasing
electrically charged ions, which attach to dust particles
in the air causing them to settle on walls, ceilings, furniture,
and draperies. Placed too near a wall, they might leave
a smudge of particles. Some units contain an optional collector
to trap the charged particles in the unit, functioning
similarly to an EAC.
Over time, however, the particles can
lose their charge and reenter the air. Like EACs, they produce
small amounts of ozone. There is little scientific
evidence supporting the effectiveness of these units.
Watch out: Do not rely on ozone generators to correct indoor air quality issues, and beware of ion generators that may be adjusted to produce high levels of indoor ozone.
The turbulent flow
precipitator (TFP) is a new proprietary technology from
Canadian-based Nutech Energy System. The device, which
attaches to the return ductwork of an HVAC or ventilation system,
contains a fan and a labyrinthine core made of aluminum
plates and synthetic fibers.
Turbulence in the air flings the suspended
particles out of the airstream where they are trapped
by a primary and secondary core, which need replacement
in one and three years, respectively. Nutech claims that TFPs
will capture 99% of particles larger than 5 microns, 97%
from 2 to 3 microns, and 90% from 0.5 to 0.9 microns. A
TFP unit with HEPA filtration is also available.
Gas Removal Filters to Clean Indoor Air
To remove gases, such as formaldehyde,
combustion fumes, or volatile organic compounds, from
the air requires the use of special adsorption media. These
media contain materials, such as activated carbon or aluminum
oxide, which trap the gases in tiny pores.
chemical adsorbents are effective with different gases,
and none is effective with every gas found in the typical
home. Relatively small quantities of activated charcoal
can be very effective at reducing odors, but how well they
filter out the low levels of multiple chemical compounds
typically found in household air is unclear.
In general the rate of adsorption of a gas is reduced as
more of the target gas is captured in the filter media. Researchers
have also found that, in many cases, some of the
gas is reemitted from the filter back into the air. Scientific
evidence about the real-life usefulness of these filters in
homes is very limited.
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Ask a Question or Search InspectApedia
Questions & answers or comments about the different types of air cleaners and filters: air purifiers.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones