Ten-point purchasing guide: in-room air purifiers; careful selection is key to this quality-of-life improvement. (Feature Article).

Air filtration not only makes air clean and pure, it also enhances a person's energy, alertness and comfort. At the same time, it helps individuals with respiratory ailments enhance their quality of life. Air purifiers also help alleviate allergy and asthma symptoms.

To make the most of this useful technology, it is essential to do some basic research before purchasing a unit. An analysis of room size, the allergens and pollutants that might be present, and any personal health concerns should be made. This article will discuss the technologies and then give 10 points to consider when purchasing an air purifier.

Available Technologies

In-room air purification systems use two basic technologies: mechanical or electrostatic filtration, or a combination of both. Both technologies are based on well-understood principles that describe airflow between obstructions (filter fibers) and the behavior of particles as they ride the airstream through the filter media.

High-efficiency particulate air (HEPA) filters use all these principles to capture particles of varying sizes. They are especially efficient at capturing the midrange particles (on which more later) that pose the greatest threat to human health. HEPA filters are recognized as effective by the American Medical Association, the American Lung Association (ALA) and the American Academy of Allergy, Asthma and Immunology.

Ten Points to Consider

The following tips and tools describe what an in-room air purification system can--and can't--do. These tips can also help with comparing performance among the hundreds of makes and models on the market.

1. Filter efficiency. In general, look for the highest percentage of particles removed and the smallest particle size captured. Filter efficiency for a particular air filter model can differ for particles of different sizes. For example, our company's hybrid HEPASilent[TM] system is rated at 99.9% efficiency at 0.3 micron and 99.97% efficiency at 0.1 micron at speed one.

Buyers need not rely solely on a manufacturer's efficiency claims. Instead, consult the Association of Home Appliance Manufacturers (AHAM), an independent industry organization that publishes the results of its overall room air cleaner performance tests. AHAM's performance tests are recognized as accurate and impartial by the Environmental Protection Agency (EPA) and the ALA. Ratings can be found online at www.cadr.org. Air cleaner performance is known as Clean Air Delivery Rate (CADR): a measure of the total volume of air that a particular air purification system cleanses of a specific pollutant in one minute. CADR test results are expressed in cubic feet per minute (CFM), with a number rating for three "yardstick" particles: tobacco smoke, dust and pollen. The higher the CADR test numbers, the better the unit's overall ability to clean indoor air.

2. Capacity. After filter efficiency, air volume capacity is key to selecting the best in-room air cleaner. The unit must be rated to handle the total volume of air in the room where it operates. This value is expressed as "recommended room size." The unit's published room size rating should be the same as AHAM's recommended room size.

AHAM room size recommendations are expressed in square feet, rather than cubic feet; they assume an 8 ceiling. If your room has an 8' ceiling, simply measure the room's length and width, multiply to obtain the square footage, and compare with AHAM recommendations.

Be sure to include ceiling height in calculating the unit's air-processing capability. Ceiling height makes a big difference in the cubic footage of a room. For example, if a room measures 10' by 22 with an 8 ceiling, you need a unit recommended for 1,760 cubic feet. For the same room measuring 10 by 22, but with an 11' ceiling, you need a unit recommended for 2,420 cubic feet.

If your room has a ceiling higher than 8 feet, you can translate AHAM's square footages into cubic feet by multiplying by 8 (the ceiling height AHAM assumes). Next, calculate the cubic footage of your room by multiplying length times width times height. Now compare your result to the AHAM recommendations. If you have high ceilings, this extra step is critical to choosing an air cleaner with adequate capacity for the room.

3. Specific health concerns. Air cleaning alone cannot adequately remove all of the pollutants typically found in indoor air. However, when combined with source removal and adequate ventilation, the EPA considers air cleaning a viable means of improving indoor air quality.

With the exception of allergens and airborne pathogens, the size of a given particle determines the degree of potential threat to human health. Generally, airborne particles are identified by the EPA as small (0.1 to 0.3 micron), midrange (0.3 to 0.9 micron) and large (1.0 micron or larger).

Small particles. Small particles (0.1 to 0.3 micron) include many viruses, bacteria, gases and chemical fumes. Although these small particles are inhaled and exhaled more easily than midrange particles, even these minute particles can irritate already compromised breathing passages and lungs.

Look for high efficiency for small particles when respiratory conditions, immune disorders or cardiovascular disease are present, and when asthma is triggered by strong odors and fumes. Some HEPA filters capture small particles; most electrostatic systems report high efficiency levels at this range.

Midrange particles. Midrange particles (0.3 to 0.9 micron) include house and textile dust, pollen, pet dander, dust mites and their feces, many bacteria, auto exhaust, mold spores and particles from laser printers and copiers.

Particles of this size present the greatest health concern because they are small enough to get past the cilia in the nasal passages and too large to be easily exhaled. Particles in this size range are more likely to become lodged in lung tissue and are suspect in a wide range of health problems related to indoor air pollution--from headaches and dizziness to cardiovascular disease and cancer.

Look for an air filter with high efficiency for midrange particles when respiratory conditions are present, when allergens are a concern and when asthma is triggered by pollen, pet dander, mold or dust mite allergen. HEPA filters generally capture midrange particles, although efficiency varies among makes and models.

Large particles. Large particles (1.0 micron and larger) are usually trapped by cilia in the nasal passages before reaching the lungs. Large particles include house dust and some of the larger pollen and bacteria.

Look for high efficiency for large particles when sinus conditions or immune disorders are present, and when asthma is triggered by pollen. All HEPA filters capture particles of this size, while electrostatic filters generally do not.

Airborne pathogens. Airborne pathogens range in size from 0.018 micron to as large as 1.325 microns. While many bacteria and viruses fall within HEPA and electrostatic capture ranges, some pathogens that are capable of movement might be able to pass through the filter media, and the mucilaginous coatings of some bacteria might affect the filter's ability to trap them.

Current concerns over anthrax bacteria have prompted a closer examination of the efficacy of home air filtration against specific airborne pathogens, as opposed to nonliving particles.

4. Legitimacy of manufacturer claims. Health organizations and government agencies rarely endorse a particular in-room air purifier brand or model. When it comes to comparing individual makes and models, the most reliable source for unbiased information is AHAM (www.aham.org).

AHAM certified performance testing results for home appliances, including room air cleaners, through a voluntary certification program. The organization's standardized test of overall performance for air cleaners (known as ANSI/AHAM AC-1) is recognized by the EPA, the Federal Trade Commission and the ALA.

As for manufacturers' claims, as with any appliance purchase, it's important to check the manufacturer's legitimacy and confirm performance claims. Commonsense red flags might include uncorroborated filter efficiency and air volume capacity statements, unwillingness to submit an air cleaner for independent AHAM testing, no physical address on brochures or Web sites, lack of detailed information of filter composition or technology, or the promise of extremely long filter life when compared to similar units.

5. Indoor environmental factors. From dust and humidity to the types of particulates likely to be present, indoor environmental conditions vary widely. Consider which types of particles affect the resident's respiratory health, as well as how environmental conditions might impact an in-room air cleaner's performance and maintenance requirements.

Dust, Some units include a built-in prefilter, which can help strain large dust particles before they fill the spaces between HEPA filter fibers. You can also trap dust by installing vent filters over central heating and air conditioning registers.

Humidity. Environments with high relative humidity levels (over 50%) are of concern when allergies or asthma are triggered by mold and mildew spores and when immune disorders are present. How filters are affected by moisture and whether they are engineered to control it are worth investigating.

Tobacco smoke. Because of its pervasiveness and the complexity of its composition, tobacco smoke is a particular challenge for current air filtration technology, as are other gaseous pollutants. When tobacco smoke is present in the indoor environment, study AHAM's CADR test results for the units you are considering. The higher the CADR results for tobacco smoke, the better the unit's ability to remove it. Keep in mind that the EPA's Office of Air and Radiation (OAR) notes that while HEPA filters can remove some tobacco smoke particles, none remove all of the 4,000 chemicals that comprise tobacco smoke.

Volatile organic compounds (VOCs). VOCs are gas particles introduced into room air through the indoor use of pesticides, glues, solvents and cleaning agents. They include a staggering variety of chemicals emitted as gases from petroleum-based solids and liquids. VOC levels can rise during remodeling and redecorating, and following pest control or aggressive cleaning activities.

In environments where VOC sources might be present, look for a HEPA filter incorporating activated carbon compounds as a filter medium. Activated carbon compounds can effectively adsorb gaseous pollutants, notes the OAR in its publication Residential Air Cleaning Devices: A Summary of Available Information. However, filter replacement is critical to avoid the eventual release of VOCs from the saturated filter. The OAR recommends changing the filters as recommended by the manufacturer to reduce the risk of "outgassing."

6. Operating cost. Replacement filters are an ongoing expense for the life of the unit. Check the manufacturer's recommended replacement interval and the filter cost, as well as any shipping charge. The OAR notes that the most effective units are generally also the most costly to purchase and maintain.

The operating expense most often overlooked when selecting an air cleaner is the energy cost. Filter efficiency claims are based on constant, rather than intermittent, operation. The energy cost of 24-hour-per-day use should be considered during the selection process. Look for the unit's energy use, expressed as watts, on the same page of the brochure, warranty or Web site where dimensions and other technical specifications are listed.

7. Construction quality. In-room air filters are an investment. As with any appliance, look for a system with quality construction, especially for internal moving components, such as fans and blowers. Check the warranty to make sure it covers internal components. The unit should be listed with an organization such as the Underwriters Laboratories or ETL and should meet U.S. standards for safety.

The durability of materials used for the cabinet is a strong secondary consideration. Because portable in-room units are subject to more handling than fixed systems, units with metal housings are likely to hold up better in the long term than units with plastic cabinets. Also, plastics generally resonate more with fans or other internal components; an air cleaner housed in a metal cabinet is likely to produce less operating noise.

8. Ease of use. Replacing filters and periodic internal cleaning, if required, can be a physical challenge for people with limited mobility or dexterity, and ease of replacement should be taken into account if residents themselves, particularly if they are in independent or assisted living, opt to assume such a responsibility.

9. Warranty. As with any appliance, choose an established manufacturer with a comprehensive, long-term warranty. Government regulations require that warranties be made available at the point of purchase, even when purchases are made through the mail or online. Most in-room air cleaner manufacturers offer a limited warranty for a specific period of time, generally from 3 to 10 years. A limited warranty covers only those components specified, and might not cover the cost of diagnosis, labor and/or shipping in the event of product failure.

10. "Bells and whistles." Operating noise can be a significant factor when using the unit, particularly in a bedroom, especially if the unit is run 24 hours per day, as recommended. Knowing this, a manufacturer might claim that its product is "whisper quiet or virtually noiseless." Confirm vague claims by requesting specific operating noise values, expressed in decibels. On the lowest setting (the typical operating speed), the quieter units are about as quiet as the average desktop computer--approximately 35 decibels.

The draft created by the unit's air-processing system is not as easily quantifiable as noise or efficiency levels. Some in-room air cleaners direct a strong stream of air from one or two exit points, while others diffuse air through many exit points to mitigate uncomfortable drafts.

While cabinet sizes vary, it is not accurate to assume that a large unit is more effective or, conversely, that a smaller unit is less effective. Efficiency is generally unrelated to size. An in-room air purifier selection should be based, first, on efficiency and air volume capacity; then space requirements can be used to narrow the choice among units of similar efficiency.

Bengt Rittri is president, Blueair, Inc. For more information, write Blueair, Inc., at 435 N. LaSalle St., Suite 410, Chicago, IL 60610; phone [phone]; send e-mail to [e-mail]; or visit www.blueair.com.