What is a HEPA Air Purifier? Understanding Air Purifier Terminology

Day to day, we don't see it or smell it. We don't taste it or invite it to settle on our clothing. Until a wayward morning sunbeam hits it just right, we don't even know for sure that it's there. But every cubic foot of air in urban living spaces contains 3 million particles of it: dust. A blanket term that refers to many types of particulates including pet dander, spores, mites, and smoke residue, dust is a stealthy enemy, especially indoors. Because most houses in America are sealed against heat losses and gains, indoor air quality suffers. Indoor air, according to the EPA, is five to six times as polluted as the air outside. A high quality air purifier is one of the most effective means to increasing indoor air quality.

Breathing Easy - Understanding Purifier Phrases

Some advertisements and even manuals will be chock full of these acronyms, so to keep them straight come shopping time, refer to this list:

HEPA Filters

Highly Effective Particle Arresting filters. These are exactly what they sound like-- dust fighting machines. These filters have been certified as capable of removing most types of air-borne allergens.

ACH Ratings

Air Changes per Hour. This rating refers to the number of times air is circulated through the filter per hour.

AHAM Accreditation

Air purifiers earn an Association of Home Appliance Manufacturers accreditation if they adhere to certain manufacturing standards. These standards are generally submitted for consideration as American National Standards, and can be found here.

CADR Numbers

CADR stands for Clean Air Delivery Rates, which are allotted by the AHAM.

VOCs

Volatile Organic Compounds are chemicals in several commonly used homecare products. Benzene, ethylene, toluene, formaldehyde, etc., all fall under this category. These chemicals, often found in paint, cleaning supplies, glues, etc., have the potential to turn into particulate allergens.

Air Purifier Types

There are four main types of purifiers available for purchase, classified by the filtering mechanism.

Mechanical

Air purifiers of this type use a HEPA filter, which health experts have found to be highly effective, and/or a carbon charcoal filter. Mechanical purifiers use a fan to pull air through the filter. This can be very efficient but also noisy.

Electronic

Using ionizers to remove suspended particles from air, the electronic purifier charges the particles and then collects them.

This process is performed in one of three ways:

Fans inside the purifier draw air into a chamber, where the particles are ionized (i.e. positively charged), and then attracted to negatively charged surfaces as the air is directed out of the air purifier. Air purifiers of this kind are called electrostatic models.

In electret air purifiers, an already-charged filter is fitted in the air purifier, attracting particles as the air passes through. The third type of electronic purifier is a negative ionizing purifier, which discharges negatively charged particles into the room, where they settle onto the couch cushions and curtains, leaving air safe to breathe in.

The electrical charge purifying process releases small amounts of ozone, which has the potential to be highly toxic, and can be especially harmful in homes with allergy or asthma sufferers.

Combination

Combination air purifiers use at least two kinds of filters, generally HEPA and charcoal or activated carbon filters, which absorb odors and gases as well. Some models might use several pre-filters, ionizers and a fan.

Hybrid Air Purifiers

Hybrids have two chambers inside of a metal box, which is then attached to the central heating or cooling duct of a home. The air passes through filters on top of the box's lower chamber, and then into the room.

Home Air Purifiers: Choosing the Right Size

As with any appliance, finding the appropriate air purifier for your home depends on many factors, including size, ratings, cost, and sensitivity of the user to particulates.

All purifiers are made for specified square footage, so be sure to take measurements of the room or rooms before buying and to purchase a purifier with either the same or larger coverage as the room size. For those who suffer from allergies or asthma, purchasing a purifier with an ACH rating of 6 or 8 is advisable. The CADR (Clear Air Delivery Rate) number is important in evaluating overall performance, and can be found in the AHAM accreditation report.

Refills and replacements are always a factor in air purification, so considering cost and frequency of replacements is important in determining efficiency. Some purifiers include dishwasher safe filters. Combination purifiers will need replacements for both types of filters at different times. Compare manufacturer's annual maintenance programs and replacement dates to ensure the greatest value. To this end, remember that purifiers must run continuously to be effective, therefore adding to the home's utility bill. Look for an energy efficient purifier, generally indicated by an Energy Star label. (See Cost section below.)

Considering the noise level of the purifier can be difficult without a demonstration, so ask in store about viewing the machine in operation. Purifiers labeled "quiet operation" may be slightly more expensive, but are ideal for bedrooms and living rooms.

Finally, as with any appliance, warranties are optional, but recommended. If the warranty does not cover motors or fans, it's much less useful to the consumer. Ideally, a warranty will also cover filter replacements, so look for a manufacturer that focuses on filter warranties, as well as motor and fan.

Air Purifier Prices & Understanding Size

Size, quality, and type of air purifier significantly affect the price range. For every 250 square feet to be covered, the purifier must be capable of processing approximately 100 CFM (cubic feet per minute). Tabletop air purifiers come in small sizes that have a 100-150 CFM rating, whereas room models generally start at 400 CFM.

Certain compact tabletop air purifiers, manufactured by Rubbermaid, Homes, and others, can give coverage for up to 200 sq ft, and are usually HEPA filter based. These can be purchased cheaply, in the $15-$30 range.

Quiet purifiers for smaller rooms (with coverage from 200 to 500 square feet) cost between $50 and $100. Again, a common feature is a replaceable HEPA filter system.

For $100 to $200, the compact purifiers will come with extra features, like replacement indicators, germicide or odor reducing filters. Climbing up the price ladder, $200 to $300 can purchase mid-sized purifiers designed for a 400 to 500 square foot space. Austin, Sharp, Whirlpool and other manufacturers tend to include quiet run and replacement indicators in these higher-end purifiers.

$300-$500 will purchase larger units capable of purifying rooms that measure up to 600 sq ft. For this price, purifiers that can be integrated with current heating/cooling systems are also available. One substantial benefit of these larger units is their sleek look, which allows the unit to become part of, rather than take away from, the room's decor.

Spending over $600 will grant consumers access to the best, most efficient, and largest range models available. These models have the ability to remove not only dust and pollen, but potentially hazardous gases, bacteria, and viruses from the home. While HEPA filters suffice for allergy and asthma sufferers, germicide filters may be useful for users with specific medical conditions.

Bottom Line

There are many factors to consider before purchasing an air purifier, most of which are specific to the user and the space. Still, nothing beats prevention. Dusting regularly, as well as refraining from smoking indoors, will go a long way toward minimizing indoor pollutants. In the event that those practices are not enough, consider all things-- size, price, type, warranty, AHAM reports, and overall value-- before choosing the purifier that will best meet your needs.