Tools and Tips

Can in-room air filtration really improve respiratory health? Will air cleaners filter out pollen and other airborne allergens? What about indoor pollutants or bacteria? How do you decide which unit to buy?

Home health care patients often ask care providers for advice concerning non-prescription techniques for augmenting overall health. Especially during allergy season, questions about in-room air filtration arise. With basic facts in mind, providers can answer their patients with confidence.

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

High Efficiency Particulate Air (HEPA) filters use all four principles to capture particles of varying sizes. They are especially efficient at capturing the mid-range particles that pose the greatest threat to human health. HEPA filters are recognized as effective by the American Medical Association, the American Lung Association, and the American Academy of Allergy, Asthma and Immunology.

To increase the percentage of small particles intercepted, electrostatic filters use an electric charge to boost the force of attraction between particles and filter fibers. Passive electrostatic filtration charges the filter media, achieving high efficiency at first and as the charge decays, efficiency gradually diminishes. Active electrostatic systems continually charge either the filter fibers or the particles, maintaining consistent efficiency levels over time.

In its publication Indoor Air Pollution: An Introduction for Health Professionals, the Environmental Protection Agency (EPA) notes that air cleaners using active electrostatic technology alone are ineffective in removing mid-range and large particles. Hybrid systems offer an effective solution. They combine mechanical and electrostatic technologies, often achieving significantly better performance than either method alone.

The following tips can help you understand what an in-room air purification system can--and can't do for patients who need to improve their respiratory health. These tips also can help you compare performance between 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 may differ for particles of different sizes.

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 their overall room air cleaner performance tests. AHAM's performance tests are recognized as accurate and impartial by the EPA and the American Lung Association. 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-foot ceiling. If your room has an 8-foot 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 feet by 22 feet with an 8-foot ceiling, you need a unit recommended for 1,760 cubic feet. For the same room measuring 10 feet by 22 feet, but with an 11-foot 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), mid-range (0.3 to 0.9 micron) and large (1.0 micron or larger).

Mid-Range Particles
Mid-range 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 mid-range 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 mid-range particles, although efficiency varies among makes and models.

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 mid-range particles, even these minute particles may 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.

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 .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 may be able to pass through the filter media, and the mucilaginous coatings of some bacteria may 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 non-living particles.

Keep in mind that any air filter model's efficiency may differ for particles of different sizes.

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 the Association of Home Appliance Manufacturers (AHAM).

AHAM certifies performance testing results for home appliances, including room air cleaners, through a voluntary certification program.

As with any appliance purchase, it's important to check the manufacturer's legitimacy and confirm performance claims before you buy. Common sense 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 on 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 particles likely to be present, indoor environmental conditions vary widely. Consider which types of particles affect the patient's respiratory health and how environmental conditions might impact an in-room air cleaner's performance and maintenance requirements.

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

Humidity
Environments with high relative humidity levels (more than 50 percent) are of concern when allergies or asthma are triggered by mold and mildew spores and when immune disorders are present.

Absorbent HEPA filter media retain ambient moisture and create an ideal internal environment for mold and bacterial growth. To combat this growth, some manufacturers recommend periodic filter sterilization or the addition of chemical-based bacteriostats.

Hydrophobic filter media counter mold and bacterial growth by eliminating moisture retention in the first place. Water-repellent fibers perform as well as absorbent fibers in the context of HEPA filtration, while remaining dry and free from water-related mold and bacteria colonization.

Tobacco Smoke
Due to its pervasiveness and the complexity of its composition, tobacco smoke is a particular challenge for current air filtration technology, as are other gaseous pollutants.

Tobacco smoke is one of the three "yardstick" pollutants in AHAM's CADR testing. 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: 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.

VOCs
Volatile organic compounds (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.

More often an industrial problem, VOCs are likely to be present in homes where graphic production, crafts involving glues and paints, photographic processing, and auto or other repairs involving solvents take place. VOC levels may rise during remodeling and redecorating, and following pest control or aggressive cleaning activities.

In environments where VOC sources may be present, look for a HEPA filter incorporating activated carbon compounds as a filter media. Activated carbon compounds can effectively adsorb gaseous pollutants, notes the OAR in its publication Residential Air Cleaners: 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 maker 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 website 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 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 Laboratory 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. Filter change can be as simple as lifting the unit's lid and sliding filters in and out, or a complicated operation involving hand tools. If the patient will be the one responsible for maintenance, it's important to take his or her physical abilities and dexterity into account.

Operating instructions should include detailed directions for filter replacement and periodic internal cleaning. Internal cleaning is a particular issue with electrostatic precipitators, in which filters are cleaned and sterilized rather than replaced.

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.

Consider both the length of the warranty and what is covered. Most in-room air cleaner manufacturers offer a limited warranty for a specific period of time. A limited warranty covers only those components specified, and may not cover the cost of diagnosis, labor or shipping in the event of product failure. Warranties range from three to 10 years.

10. Bells and Whistles
Operating noise can be a significant factor in sickroom use, especially if the unit is run 24 hours per day as recommended. Knowing this, a manufacturer may claim that their product is "whisper quiet" or "virtually noiseless." Confirm vague claims by requesting specific operating noise values, expressed in decibels.

The draft created by the unit's air processing system is not as easily quantifiable as noise or efficiency levels. Generally, a draft must be evaluated by seeing, or feeling the unit in operation. 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.

Evaluate the space required for the unit. Note that 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. Your in-room air purifier selection should be based first on efficiency and air volume capacity; then, use space requirements to narrow the choice between units of similar efficiency.

Don't forget to check operating instructions for placement advice. Most units require specific clearance from walls and windows in order to operate effectively. Look for a unit that physically fits within the environment in which the unit will be operating.

In conclusion, in-room air filtration is recognized as a legitimate tool for improving personal and public health by the Environmental Protection Agency, the American Medical Association, the American Lung Association, and the American Academy of Allergy, Asthma and Immunology. To make the most of this useful technology, it's essential to do some basic research before you buy--including an analysis of room size, the allergens and pollutants that may be present, and, of course, the patient's health concerns.

This article originally appeared in the March 2002 issue of HME Business.

HME Business Podcast