The Seven Sins of Air Filter Manufacturers
by Frank Hames, President -
IQAir, North America
With estimated sales of over 4 million units in 1999 in the United
States, room air purifiers have become standard appliances in many
households and offices. Manufacturers of room air purifiers must
strive - harder than anyone else in the air purification industry -
to provide low cost products to their consumers. This has resulted
in air cleaners with HEPA technology selling for as little as
$80.00. While making air cleaning technology affordable is a
commendable goal; misleading marketing statements and questionable
air cleaning performance have disenchanted many users.
This article attempts to draw attention to a number of deceptive
marketing practices that air purifier manufacturers use, which are
detrimental to the credibility of the air cleaning industry as a
Since the science of air cleaning is a complex one, finding one's
way through the maze of unsubstantiated claims and misinformation is
a difficult task even for the most alert and critical consumer.
Seven common industry practices in particular continue to confuse
consumers and air cleaning professionals.
1. Theoretical HEPA Efficiency vs. Actual System Efficiency
Due to the high efficiency, reliability and proven track-record,
HEPA technology has become the industry standard for particulate
filtration in critical environments, such as semi-conductor clean
rooms and hospital operating rooms.
Recognizing the great marketing potential of the term "HEPA", many
manufacturers are using it to project a high- performance image onto
their room air purifiers. What most HEPA-based air purifiers
manufacturers conveniently omit to tell the consumer, is that their
air purifiers provide nowhere near the performance level of
professional HEPA filter systems used in hospitals and clean rooms.
Often consumers are misled about an air purifier's efficiency in
removing pollutants. Statements like "effectively removes 99% of all
airborne allergens" or "efficiently scrubs the room free of air
pollutants", lead consumers to believe that these air purifiers
remove virtually all of the impurities from the air in a normal
Claims about HEPA-based air purifiers often claim 99.97% filtration
efficiency. In most cases, this is also not true. The actual
efficiency, for particles of 0.3 microns or larger, of many HEPA-based
air purifiers sold today is below 80%. The "99.97%" refers to, in
most cases, the theoretical efficiency rating of the filter paper
that is used in the air cleaning device at 0.3 microns or larger.
The performance gap between HEPA-based room air purifiers and
professional HEPA filter systems is mainly due to cutting corners in
mass-production and profit maximization. There are a number of
reasons why most HEPA-based room air purifiers do not achieve actual
HEPA-rated filter media is not used.
The HEPA filter media gets damaged during the pleating process (HEPA
media breaks easily).
There is leakage between the pleated HEPA filter pack and the filter
There is leakage between the HEPA filter frame and the air purifier
Only very few manufacturers state the actual overall efficiency of
their device, and even fewer guarantee and certify their air
2. Overstating Actual Air Delivery Rates
Even the most efficient room air purifier in the world would not
impact a room's air quality level if it were not able to pass enough
air through its filters. The amount of air that an air purifier is
able to process (air flow rate) is usually expressed in cubic feet
per minute (cfm). Consumers are often misled by exaggerated or false
claims by manufacturers regarding air flow rates.
One common trade practice is to state the free-flow air handling
capacity of the fan motor (i.e. without filters installed), rather
than the actual air flow rate (i.e. with all filters installed).
Many manufacturers don't even make this vital air purifier statistic
available to consumers. Instead, many state a suitable room size,
without mentioning how many air changes per hour the air purifier
would manage to produce in that size room.
Only very few manufacturers state the actual airflow rate of their
device (with all filters installed), and even fewer guarantee and
certify their air purifier's air flow rate.
3. ULPA is NOT Better than HEPA
In an effort to differentiate air purifiers from the mass of HEPA
air purifiers on the market, some manufacturers have introduced air
purifiers, which supposedly use ULPA technology. ULPA stands for
Ultra Low Penetration Air and is used in modern clean rooms. The
difference between HEPA and ULPA is the efficiency rating of the
filter media. Typical HEPA filter media has an efficiency of 99.97%
at 0.3 microns, whereas ULPA media has an efficiency rating in
excess of 99.999% at 0.12 microns.
Stressing the higher efficiency at smaller particle size,
manufacturers of ULPA-based air purifiers claim that these devices
are superior to HEPA-based air purifiers. Unfortunately, this is a
perfect example where the search for a better sales pitch has
resulted in an inferior product, since the reverse tends to be the
case. All things being equal, an air purifier that uses ULPA filter
media will be less effective in reducing the particle concentration
in a typical room, than the same air purifier equipped with HEPA
filter media. And as with many HEPA-based air purifiers, many ULPA-based
air purifiers come nowhere close to actually delivering 99.999%
While ULPA filter media has the potential to remove more particles
than HEPA filter media, that advantage is lost in room air
purifiers, due to the reduction of air flow caused by the denser
ULPA filter media. ULPA filter media typically allow 20-50% less air
to pass than HEPA filter media, resulting in fewer air changes per
hour in a given room.
4. Ineffective Gas Phase Filtration
In many cases room air purifiers are purchased to deal with gaseous
contaminants and odors. So it comes as no surprise that most
manufacturers claim to use some technology to reduce gases and
odors. The most common technology adopted by air purifier
manufacturers for the removal of gaseous pollutants is activated
carbon. While activated carbon in its granular form is
unquestionably effective for the removal of many gaseous
contaminants, most room air purifiers on the market today use carbon
fiber pads, which are only impregnated with activated carbon dust.
These filter pads contain only a few ounces of actual activated
carbon and as a result, are essentially ineffective for the removal
of gases and odors.
Some manufacturers claim that their activated
carbon filter eliminates all gaseous pollutants and odors, a feat
that is scientifically impossible. Specific gaseous contaminants
need specific gas phase filtration technology. Activated carbon does
not efficiently adsorb low molecular weight gases. For this reason,
special sorbents are needed to effectively deal with pollutants,
such as formaldehyde, hydrogen sulfide and ammonia.
Many room air purifiers that use granular activated carbon also use
Zeolite. Zeolite is a natural mineral, whose pore structure is
supposed to be better suited for the removal for gaseous compounds
like formaldehyde and ammonia. In fact, there is no reliable
scientific evidence to show that zeolite is able to remove any
gaseous compound better than specialty impregnated carbons or
impregnated alumina. So why is Zeolite used? Zeolite is an
inexpensive "filler" that is less expensive than activated carbon.
Secondly, the concept of using two different substances to control
gases and odors sounds quite promising to the unsuspecting customer.
5. Sacrificing Long-Term Performance
While most tests and evaluations of air purifiers assess only air
purifier performance during its first few hours of usage, the real
test for air cleaning effectiveness is long term performance.
Unfortunately, most manufacturers cut costs on features that would
enhance long-term performance.
One standard industry practice is the use of ineffective pre-
filtration. In HEPA based air purifiers, it causes the HEPA filter
to become clogged at a rapid rate. This in turn reduces the air flow
rate, thus resulting in fewer air changes per hour in a given room.
This is a particularly serious issue, since some manufacturers
inform their consumers that their HEPA filters will only need
replacing every 3 to 5 years.
Insufficient pre-filtration, also, causes air purifiers with
substantial granular activated carbon filters to quickly lose their
gas phase adsorption potential. Dust particles - that should be
trapped by pre-filtration - clog the miniscule pores of the
activated carbon, and destroy its holding capacity to adsorb gases.
Another reason for poor long term performance of air purifiers is
that some air cleaning technologies suffer drastic reductions in air
cleaning efficiency without regular maintenance or frequent filter
Air purifiers with electrostatic precipitator technology experience
drastic efficiency reductions as the collector plates become covered
with particles. Air purifiers that use electrostatically charged
fibers (electrete) also rapidly loose filter efficiency with
particulate loading, especially in the presence of tobacco smoke.
6. Frequent and Expensive Filter Replacement
While the initial purchase cost for many room air purifiers is
relatively low, the cost of replacement filters can be substantial.
Here are some reasons why many air cleaners require frequent and
expensive filter replacement:
Lack of effective pre-filters that protect activated carbon and HEPA
filters from premature clogging.
Use of small filter cartridges with low holding capacity for
Filter replacement instructions that base filter replacement
intervals on time passed (e.g. every 6 months) rather than actual
usage and degree of air pollution.
Combining several different filter stages in one filter cartridge,
thus forcing the user to replace all filters at once, even if only
one filter stage is used up.
7. Trying to be All Things to All People
While many air purifier manufacturers offer several models, these
models often vary only in size, rather than air cleaning technology.
And since manufacturers like to have their product appeal to as many
potential customers as possible, they sell one and the same unit as
the ideal solution for pet allergens, pollen, mold spores,
microorganisms, tobacco smoke, odors, traffic fumes and chemicals,
etc. In fact, some manufacturers claim that by virtue of using a
multitude of filter stages their air purifier is more effective.
Unfortunately, the effectiveness of the air purifier suffers,
because more filter stages mean higher air resistance and lower air
delivery. Air purifiers that only contain filter stages matched to
the user's requirements, offer superior filtration efficiency and
Conclusion Industry organizations, like AHAM, have set out to
establish some reference point for air purifier performance, they
have not succeeded to make comparison shopping for air purifiers a
simple task. AHAM's testing protocols do not evaluate actual
particle retention, gas phase filtration or long-term performance of
So what are the lessons when evaluating air purifiers? Don't believe
every claim made by manufacturers. Realize that a $80 air purifier
will have serious limitations. Ask manufacturers to substantiate
their claims with independent evidence. Check the underlying
technology and investigate whether it has been properly implemented.
Use tools that allow objective evaluation of air cleaning
performance, such as laser particle counters, to check
manufacturer's particulate efficiency claims and evaluate actual
Misleading claims regarding air purifiers and air filters have in
the past led to decisions and orders of the Federal Trade Commission
against manufacturers, and are likely to do so in the future unless
manufacturers practice better self-restraint and self-regulation.
Participating in sound business practices and making scientifically
proven claims will restore lost faith in room air purifiers,
allowing consumers to make informed purchase decisions - based not
only on price but, also, on actual performance.
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