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Tuesday, January 19, 2010

Air cleaners and filters - A rostrum

We focus this week on a Rostrum contribution, "Air filters and air cleaners: Rostrum by the American Academy of Allergy, Asthma & Immunology Indoor Allergen Committee," by Sublett et al. (J Allergy Clin Immunol 2009;125:32-38). The authors tackle the topic of air cleaners and air filtration by providing technical information on efficiency testing, and specifications of available technology as well as summarizing a literature review on the effects of air cleaning on asthma and allergy. Two air cleaning modalities are covered: portable room air cleaners and whole-house systems installed in HVAC units. The published studies reviewed by the authors typically presented findings from a single method air cleaner across short durations up to 6 months. The authors note that most results demonstrated minimal or no benefit. Overall, HEPA-filtered, portable air cleaners, and HVAC filtration systems that used high-efficiency filters and frequent routine maintenance had limited benefits. Sublett and coauthors suggest that air cleaning should be viewed as mitigation of disease progression rather than treatment for asthma and allergies. The authors go on to conclude that short-duration, single-method studies are not enough to demonstrate mitigation and that long-duration studies involving multiple air-cleaning methods are needed.

Do you have any questions for the authors, or comments about this study? We want to hear from you. Please feel free to post your own questions or comments. All questions and comments will be forwarded to the authors for a response.


  1. Dr. Robert Bush comments: "The authors conclude that 'there is sufficient evidence that air filtration does reduce indoor levels of ambient particulates that might trigger disease processes themselves.' Based on this statement, to which patient should the clinician recommend an air filtration device? HEPA filtration for everyone with respiratory symptoms?"

    Dr. James Sublett, corresponding author on the rostrum, responds: "Based on our review of both the medical and non-medical air filtration literature it appears that effective air filtration can reduce levels of small airborne particles known as particulate matter (PM) that may enter the breathing zone of the occupants of a dwelling. Many allergens reside in the settled dust, but are known to become airborne when disturbed and can be part of the particulate cloud. In addition, it is recognized that some allergens may stick to and “hitch a ride” on PM. Any means to reduce the total exposure levels should be considered. Source control is the first approach (removal of indoor animals, no smoking, etc.)
    It is my opinion that the best option for patients with respiratory symptoms is a combination of whole-house filtration, plus a HEPA air cleaner placed in the bedroom (Combination therapy?) Disposable MERV rated HVAC (furnace) filters are a cost-effective measure for whole-house filtration. HEPA air cleaners are found in a myriad of sizes, designs, and pricing. As mentioned in the rostrum, they should be of the proper size for the room . Laminar flow HEPA devices designed to clean only the breathing zone while sleeping also seem promising. It is important that the patient understands that air filtration is only one of several steps to be used as avoidance measures."

  2. We asked the authors of this rostrum to share any thoughts or insights regarding this report. Here are their replies:

    Wanda Phipatanakul, MD:
    “We have conducted a comprehensive view of the air filtration studies and mainly have shown that there are varying degrees of efficacy noted in these trials and that more rigorous, randomized controlled clinical trials of appropriate length, sample size, and patient population need to be done to show true health effects. Furthermore, air filtration may be a useful adjunct to multi-faceted global interventions in decreasing disease morbidity caused by environmental factors. Furthermore, technologies to improve efficiency of air filtration devices may be needed and further studies to understand the role of air filtration techniques in a variety of multi-faceted and concentrated efforts on decreasing harmful environmental exposures are needed.”

    James Seltzer, MD:
    “We also need to keep in mind the state of the art of air filtration itself, e.g., high efficiency filters may be available for use in residential forced air units, but these filters may not be good for your furnace - the resistance across the filter may strain and overtax the FAU's motor and shorten the life of the furnace or air conditioner.”

    James Sublett, MD
    “Dr. Seltzer’s point is a good one. Older HVAC systems may have blower fans that are not sized correctly for adequate ventilation, especially with some of the newer high efficiency filters. Fortunately there are newer non-woven filter medias that allow high efficiency with good air flow. There are three basic components that are important for a furnace filter that should be balanced for the best performance: 1.)loading capacity (how much dust the filter will hold before blocking air flow); 2.) pressure drop across the filter when new (determines the amount of air flow/ventilation allowed by the filter) and finally 3.)the efficiency of the filter.”

    Robert Burkhead, PE
    “I've been designing, developing and testing air filter products for over 30 years and quite honestly, am amazed at how little attention goes into dealing with the real issue at hand - that is making the air we breath as healthy as we can make it. There are two issues in my mind - capitalism and creative thinking:

    Jim and I have discussed this over many a breakfast and lunch meeting, there is no organized push to address this broad IAQ issue for a very simple reason. There's no 'easy' money in it. Every product or technology success you can talk about is rooted in financial success or you would not even hear of it.

    No point in arguing virtues or viles of capitalism, the point is, when an IAQ idea can be orchestrated into financial reward, only then will it progress. Wanda is clearly on track when she notes that real efficacy must be shown in reasonable and defendable study. That "tool", used as a marketing hammer, will be the grease that pushes meaningful change.

    If we can accept that the real goal is providing healthy air to breathe for as many people in the world as we can, then quite honestly, barrier filtration really isn't the place to focus our talents. Barrier products exist now that virtually eliminate ANYTHING from the air. In terms of performance, there is nowhere else to go! So we need to focus on the real issues, source control, ventilation, passive systems that don't require that we extract all the air from a room, clean it
    and then return it to the room. Coupled with legitimate proof that the elements are effective, THEN real progress will be made.

    Please forgive my rigor - I don't often get an opportunity to vent to folks I respect.”

  3. Most quality HEPA air cleaners will include between 3 1/2 and 15 pounds of activated carbon. It is important to replace the carbon as needed. The lesser the carbon the more often it should be replaced.

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  4. Every air cleaner are really dedicated for effective air cleaning and air purifying.The efficiency is the most to consider on buying the machine.

  5. Comprehensive post on air cleaner. Preventive measures for allergens like air filter is very important. It boost the quality of indoor air and provide clean air suitable for breathing.


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  7. Thanks for sharing. HVAC is the main issue for house in summer.

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  8. Air cleaners/ filters must be cleaned in 3 months. That was just an amazing article.

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  9. I have spent a lot of the time in different blogs but this is really a unique blog for me.

  10. Cleaning air ducts makes a lot of sense, at least in theory. Because dust gradually accumulates on virtually every surface, doesn’t it stand to reason that it would build up to an intolerable degree.

  11. Hey what a brilliant post I have come across and believe me I have been searching out for this similar kind of post for past a week and hardly came across this. Thank you very much and will look for more postings from you. Best Air Purifiers