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The Physics Of Effective Air Cleaning

Welcome to the National Allergy Newsletter. This month I'm discussing How Understanding The Physics Of Effective Air Cleaning Can Help You. I confess, I did not make many A's in my high school or collegiate physics courses, but hopefully that won't keep you or me from understanding that effective air filtration is more than just a filter and a fancy looking device. There are lots of numbers, claims and factors to sort through when considering the best way to clean your home's air. So whether you're in the market for an air purifier or already own one, I'll try to walk you through some questions to ask, terms to know, and simple ways to get the most out of any room air cleaning device.


Katie Weaver & The National
Allergy Newsletter Team

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Whirlpool Room Air Purifier Sale

Whirlpool Air Purifiers Are On Sale
Until April 30, 2007

One of the most effective ways to reduce pollen and other airborne allergens in your home is with a room air purifier, and Whirlpool is a great choice.

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    How Understanding The Physics
    Of Effective Air Cleaning Can Help You

    Do I Need An Air Cleaner?

    Room Air Purifiers Remove Airborne Allergens (Like Spring Pollen) From Your Home A common mistake for many allergy sufferers is to assume that buying a room air filtration device will greatly reduce their home's dust mite problem. In fact, dust mites in any given room like to stay where it is warm and humid, and where they have a food source. That means mites and their allergens are mostly confined to mattresses, pillows, carpets, and furniture, and are not likely to be drawn in to an air purifier and filtered like many other airborne allergens.

    A good room air cleaner is most effective for filtering mold spore, cat dander, dog dander, pollen and other small floating particles. In other words, if you are feeling the effects spring pollen, chances are that a room air cleaner could offer you some relief.

    Even if you're not sensitive to molds or pollen, there are also purifiers made especially for removing harmful gases, pollutants, odors, and chemicals. Many chemically sensitive individuals, city-dwellers, or those sensitive to odors find that specialized purifiers are a must-have for living symptom-free.

    If your doctor has recommended that you get a room air cleaner or you have decided that it would be a good move for the health of your family, the Environmental Protection Agency (EPA) says the following factors are important to consider regarding the performance of an air cleaner. For further explanation of each point, keep reading as I go further in depth on each of these issues.

    1. The percentage of the particles removed as they go through the device (that is, the efficiency).
    2. The amount of air handled by the device.
    3. The effective volume of the air to be cleaned.
    4. The decrease in performance which may occur between maintenance periods and if periodic maintenance is not performed on schedule.

    5. Source:

    What Filtration Method Does National Allergy Recommend?

    The air purifiers that we sell at National Allergy all move air through filtration media. This method is what most doctors recommend, and what we have found in our testing to be most efficient and cost-effective. HEPA (High Efficiency Particulate Air) is the most common filtration media used in air purifiers. Originally developed during World War II, HEPA was used to prevent the discharge of radioactive particles from the exhaust of a nuclear reactor facility. This medium has since become a vital technology in industrial, medical, and military clean rooms and has almost become the standard in portable residential air cleaners. A true HEPA filter is usually pleated to allow for maximum surface area and, by definition, must remove 99.97% of particles at least 0.3 microns in size - as small or smaller than pollen, pet dander, mold spore and some smog particles.

    Using HEPA as a benchmark, some companies like 3M have developed similar filtration media (Filtrete) that is as efficient as HEPA media. Be sure to check the particle filtration efficiency of an air cleaner before buying.

    Other available filtration technologies include electronic electrostatic machines that use electronically charged collecting plates to attract particles found in the air. There are two general types of electrostatic room air cleaners: those that have motorized fans to circulate room air and those that don't. I'll say more about the importance of air movement later. Generally speaking, any electronic electrostatic machine will rapidly loose effectiveness as dust builds up on the plates. While you may save some money on replacement filter costs, we have found that electrostatic plates need to be cleaned as often as every week in order to maintain their effectiveness. In addition, many electrostatic purifiers can produce ozone as a by-product. According to the EPA:

    When inhaled, ozone can damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath, and throat irritation. Ozone may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections.
    And for this reason, we discourage the use of ozone generators because of their potentially harmful side effects.

    Another type of air cleaning technology is found in ionic precipitators. These machines are usually small, tabletop units that dispense ions into a room. The ions find and attach themselves to particulate matter in the air. These newly formed particles maintain their charge and then seek out a surface and attach to it thereby "precipitating" out of the air. Usually these surfaces are nearby walls or furniture that may need to be wiped down periodically because particles collect on them.

    National Allergy carries three ionic precipitators developed by Wein Products. We recommend the Wein 2500 for basement and crawlspace use, particularly for removing airborne mold spores and mildew. Chronic sinusitis sufferers in particular can greatly benefit from reduced mold and mildew. (Our precipitators produce only extremely low and, therefore, safe levels of ozone).

    Some air purifiers available today blend the technology of high-efficiency filtration media, with ionization to increase the overall efficiency of their purifiers. Blueair is a well-known manufacturer utilizing this hybrid technology that filters incoming air, while emitting ions to bind to even the tiniest particles and prevent them from escaping past the filters. Blueair air purifiers emit NO ozone due to the design of the sealed ion chamber.

    Finally, for those sensitive to environmental pollutants like smog, chemicals and odors, some room air cleaners offer additional filters made from activated carbon, in either granulated or blanket form. Zeolite and potassium iodide are other compounds used for chemical filtration. Our Austin Air HealthMate Plus and IQAir Multigas GC units are built especially for this purpose.

    Air Flow Is An Important Factor For Air Purifier Efficiency Why Is Air Movement Important?

    By what method does a silent, non-motorized air cleaner bring particles to itself for capture? If you're not sure, you're not alone. But an air cleaner with a strong motor stirs up the air throughout the entire room causing dirty air in the far corner to be carried to the unit for purification. Plus, unpurified air is constantly introduced into a room, so having a hard-working fan to continuously re-circulate air ensures that all air is being filtered. Also, in heavily trafficked rooms allergens are repeatedly kicked up, so it is important to have a purifier that can effectively pull those airborne particles into its filters before they re-settle.

    Because air movement is so important to the effectiveness of an air cleaner, National Allergy does not recommend that allergy sufferers use air purifiers that are not motorized. And we are not alone: according to the EPA, "A very efficient collector with a low air-circulation rate will not be effective." So if the air purifier's fan motor is not drawing particles through the filter, it doesn't matter how good the filter is.

    In a comprehensive review of a multitude of air purifiers, a leading consumer publication found that a well-known tower-design electrostatic unit was quite inefficient at removing airborne particulates, while another electrostatic machine was their top-rated pick. The difference? The slim, quiet tower unit only used charged collecting plates with no means of passing air through them, while the top-rated unit generated efficient air movement in the room. It should also be noted that that same article ranked the Whirlpool AP450 as the top HEPA Room Air Cleaner. (Remember: Whirlpool Air Cleaners are ON SALE until April 30.)

    What Size Purifier Do I Need?

    The size - which really reflects the effective volume of air the machine can clean - depends on the size of the room you plan to clean. We test every air purifier that comes in our door for many things, and one of the measurements we and other authorities use is Air Changes Per Hour. This measures the number of times each hour that an enclosure's total volume of air is exchanged with fresh or filtered air. Our target value is to have an air cleaner produce 5-6 air changes per hour with high filtration efficiency. The key for you to maintain this value for your purifier is to use it in an appropriate-sized space. In other words, do not use an air cleaner designed to clean a 10' x 10' room in a 20' x 20' room. The cleaner may only generate 2-3 air changes per hour, which means the allergen count in the room will never be as low as it should be. And remember, there's no danger of over cleaning a room's air. So putting an air cleaner that can produce 6 air changes per hour in a large room into a small room only increases the number of air changes per hour and that's a benefit. Visit our Air Cleaner Comparison Chart to see recommended room sizes for all the purifiers we offer.

    Doctors recommend starting your allergen-control regimen in the bedroom. Realize that the most effective fan-driven air purifiers are going to produce some noise. The more area your area purifier can clean, the more noise it will to produce. Today's manufacturers know that some people will be concerned about noisy air cleaners, so most air cleaners on the market today have variable speeds. Air Purifiers Can Be Just A Pleasant White NoiseJust remember, the published room size recommendations of your purifier assume that you'll be running it on high. If you are planning on only using low or medium settings, you should consider a higher-efficiency cleaner.

    If you are concerned about noise keeping you awake, run the air cleaner on high during the day when are not in the bedroom and keep the door shut, then utilize a lower setting at night. For excellent filtration at low decibels, I recommend Whirlpool Whispure (Remember: Whirlpool Air Cleaners are ON SALE until April 30), Filtrete Ultra Clean or Blueair air purifiers. They have great sound insulation, so even on the highest setting they are really nothing more than low background noise.

    Most of our customers would probably say the extra noise is a small price to pay for the peace of knowing they are breathing cleaner air. In fact, I find that I can't sleep without the gentle "white noise" my purifier provides.

    How Do I Get The Most From My Air Cleaner?

    Two other key factors in getting the most from your air purifier are proper placement and regular maintenance.

    Proper Placement. Machines like Whirlpool Whispure (Remember: Whirlpool Air Cleaners are ON SALE until April 30) and Filtrete Ultra Clean have front air intakes so they can be placed against a wall and still circulate air effectively. Other machines feature 360-degree air intake and are best placed 2 to 3 feet away from a wall. We recommend units which vent clean air upward or from the top of the unit to enable the most effective air circulation and to avoid stirring up dirt and allergens by blowing air across the floor. The area around the air intake should be free of furniture, houseplants or other obstructions. Likewise, you should also follow manufacturer recommendations about placing items on top of your purifier that could inhibit the expulsion of clean air. Changing Filters As Recommended Means Optimum Performance From Your Air Purifier

    Maintenance. Any air cleaner that utilizes a high-efficiency media filter will require filter changes. Maintenance varies on every machine. The Filtrete Ultra Clean Air Cleaner from 3M has a single replacement filter, while the IQ Air HealthPro units have multiple filters. Many purifiers that we carry come with filter change indicators to make maintenance easier to remember. Failing to change the filters on schedule reduces the effectiveness of your air cleaner, and can eventually cause motor damage. In addition, some manufacturers will void warranties on machines that have not been properly maintained. National Allergy has all available replacement filters for the brands we sell and for some other air purifiers, too.

    I wish you the best of luck this spring season with your allergies. Hopefully you can find a way to integrate a room air cleaner into your allergen avoidance regimen. And don't forget to let us know about your allergen avoidance success stories!

    National Allergy E-Mail Newsletter The information in this newsletter is for educational purposes only. Always consult with your doctor first about your specific condition, treatment options and other health concerns you may have.

    Remember that our customer service representatives have plenty of experience guiding people through the options for allergy, asthma and sinus relief, so feel free to contact us by calling one of our phone experts at 1-800-522-1448 Monday through Friday between the hours of 9:00 am and 5:30 pm Eastern Time. You can also e-mail us at


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