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The CDC and the Biden administration are urging communities to reopen schools as quickly as possible. 

But according to the CDC's own data, only 4% of America’s schoolchildren live in counties where transmission is low enough for full-time in-person learning without additional restrictions, reported the New York Times. 

As a result, both parents and teachers are quite reasonably worried about resuming in-person learning as new COVID-19 variants emerge. 

“This is the biggest adaptive challenge in my career and in the history of public education,” said Cindy Marten, superintendent of San Diego public schools in the New York Times.

One thing is certain—coronavirus transmission is airborne, so air quality is critical. This article focuses on: 

  • How HEPA filtration and adequate airflow can reduce COVID-19 risk
  • What 3 factors matter most when selecting school air purifiers
    1. Effectiveness – Can it capture COVID-19 particles throughout the room?
    2. Quietness – Will its noise cause disruption and learning loss?
    3. Operating Cost – Is it efficient and warranty-protected?  

    “In-person learning is essential, so we’re proud to be helping more than 300 school districts and universities reopen safely,” said Andy Graham, CEO of Alen Air Purifiers. “We prioritized supply and support to schools because we’re not just air quality experts, we’re parents, too” 

    The Big Picture

    Doctors and scientists believe schools can reopen safely under certain conditions. Still, there's one thing we must not overlook: How adequate airflow and effective HEPA filtration can work together to decrease risk by keeping airborne viral concentrations to a minimum. 

    "At my school, teachers and students wear masks, practice social distancing, and classrooms are sanitized between classes,” said Middle School Teacher, Angelyn Moore. “Even with all of that, I was cautious about returning to work. Having the Alen air purifier in my classroom has given me such confidence returning to school."


    air purification air flow inforgraphic

    How Coronavirus Accumulates Indoors

    The science is clear: coronavirus spreads via aerosol droplets indoors. Shared spaces occupied for prolonged periods pose one of the most acute risks. And Airborne virus particles don’t social distance—they float up to 60 feet, according to experts. 

    Studies have “demonstrated beyond any reasonable doubt that viruses are released during exhalation, talking, and coughing in microdroplets small enough to remain aloft in air and pose a risk of exposure at distances beyond 1-2 m (3-6 feet) from an infected individual… traveling tens of meters (30-60 feet), much greater than the scale of a typical room.” 

    Why People Catch COVID-19 Indoors

    According to Dr. Erin Bromage, the Dartmouth Immunology and Infectious Disease professor who emerged as an authority on airborne transmission, the Golden Rule of indoor COVID transmission is this:


    In other words, the degree of concentrated exposure over time is the crucial factor. Indoor spaces account for 90% of all transmission events, Bromage wrote, and any enclosed environment with poor air circulation and a high density of people spells trouble.

    Social distancing guidelines don't hold in indoor spaces where you spend a lot of time, as people on the opposite side of the room were infected,” said Bromage. 

    COVID air movement in classrooms

    air movement in classrooms

    Airflow visualizations with and without outside ventilation and an air cleaner, courtesy NY Times 

    How HEPA Captures Viruses & Reduces Risk

    True HEPA (High-Efficiency Particulate Air) filtration is the most effective air-purifying technology available. It’s used by hospitals, high-tech clean rooms, and scientific labs as a proven method of removing airborne impurities. 

    The CDC recommends using portable HEPA air purifiers like Alen alongside other best practices as “part of a plan to protect people indoors.” The EPA states that “air cleaning and filtration can help reduce airborne contaminants, including particles containing viruses.” 

    Alen’s True HEPA (H13) filters capture over  99% of virus particles, according to independent lab testing. In microbiology tests by LMS Technologies, the Alen BreatheSmart 75i:

    • Captured over 99% of virus particles from a 1,050 Ft3 test chamber within 20 minutes. 
    • Captured over 99% of particles in the COVID-19 particle size range (0.06-0.125 microns). 
    Bioaerosol testsused an FDA-approved live COVID-19 proxy (MS-2 bacteriophage). 


    alen graph


    Alen BreatheSmart 75i True HEPA Air Purifier From $749

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    Alen BreatheSmart 45i True HEPA Air Purifier From $429

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    To effectively purify a room, you must move a lot of air 

    Particles simultaneously float and settle. So, a purifier must be able to clean and circulate a room's full volume of air.  Extra airflow from open windows and HVAC vents can help disperse particle concentrations (as long as infected air isn’t blown directly from person to person).  

    Inside an enclosed ‘box,’ millions of viral particles become more concentrated with every breath—even with a mask on—unless they are dispersed by airflow,” said Alen CEO, Andy Graham. “Shared-air indoor spaces need their own air purifiers to effectively trap the virus within each ‘box’ in tandem with HVAC airflow.

    Here’s how HEPA purifiers capture virus particles: 

    1. Ultrafine virus particles are carried by aerosol droplets.
    2. Small droplets quickly spread up to 16 feet before evaporating, leaving virus particles floating weightlessly to circulate further.
    3. A HEPA purifier with sufficient airflow capacity for the room draws in virus particles.
    4. Trapped viruses die (or lose infectiousness) inside the HEPA filter within hours/days. 

    How to Shop for  HEPA Air Purifier for Schools 

    Picking the right HEPA purifiers to protect students, faculty, and staff may seem like a daunting task. We’re here to help. Let’s look at the most important aspects of a school air purifier.

    A classroom room ideally needs at least four full-volume air changes per hour (ACH) for the maximum degree of safety, according to Harvard Health. For that reason, a purifier MUST not only have powerful airflow capacity but be able to work quietly. Here at Alen, our engineers have been perfecting that formula for over 15 years. 

    Top 3 must-haves for school air purifiers 

    COVID Effectiveness: Purify the entire room multiple times per hour 

    • Demand independent lab data to back up COVID capture claims
    • Look for a high Clean Air Delivery Rate (CADR) to demonstrate power 
    • Choose a purifier that blows air upward, not frontward, to avoid cross-contamination 

       Quietness: Noisy purifiers cause distraction and learning loss  

      • Purifiers base coverage on top speed. How noisy is that?
      • Alen school purifiers are 2X quieter than competitors with similar airflow (49 dB) 
      • Hearing experts says noise above 70 decibels can disturb learning 
        Value: Schools deserve low operating costs & lifetime coverage   
        • Demand ENERGY STAR Certified efficiency  
        • Look for a lifetime warranty & in-house support  
        • Consider filter life: Alen True HEPA filters last up to 15 months

        Our purifiers add a proven layer of protection and peace of mind for students, teachers, and staff in over 30,000 classrooms nationwide,” said Shelley Johnson, Director or Alen’s EduSafety Team. “With the quietest large HEPA air purifiers on the market, Alen is a proud partner in public safety.” 

        How to Calculate Purifier Size Needs: Bigger is Better for Safety 

        Figuring out what size purifiers are right for each classroom use is simple. Harvard's Health recommends between 4-6 air changes per hour (ACH) to effectively and consistently purify the air in a classroom. To calculate the ACH, you only need two things: 

        • The dimensions of the classroom you want to purify 
        • The Clean Air Delivery Rate (CADR) of an air purifier   
        ach formula

        If the purifier you are considering can achieve at least 4 ACH, then it can provide an adequate level of protection, according to experts. But BEWARE of excessive noise. Clean Air Delivery rates are based on a purifier’s highest speed. How loud is that?  

        According to national standards, noise above 70 decibels (dB) can disturb learning. As a point of reference, the Alen BreatheSmart 75i emits 49 dB at its highest speed, achieving 5.1 ACH in a 450 SqFt classroom with nine-foot ceilings.   

        Real World Case Study: Redeemer School 

        school classroom with air purifier

        The Early Childhood Center at Austin’s Redeemer Lutheran School provides an essential community service, offering pre-K education for many professionals in healthcare, government, other fields unable to work from home. Alen helped Redeemer ensure its 15 classrooms were filtered to Harvard Health standards using our compact BreatheSmart FLEX HEPA air cleaners. Here's the breakdown:

        alen chart

        Parents are so appreciative that we’ve added the purifiers,” said Amber Schraeder, Director of Redeemer Lutheran School. “They say it makes them feel even more confident about their child their child coming to school in the midst of a pandemic.” 

        TOP 3 TAKEAWAYS:  Best Practices for Safer Schools

        1. Practice  cohorting  to avoid overcrowding and limit spread: The CDC recommends that groups of students, teachers, or staff form cohorts or ‘pods’ that stay together throughout the school day to minimize exposure across the school environment. 
        2. Prioritize airflow:  Ample ventilation can disperse the virus - Be outside when possible. Wind, even in perceived stillness, can rapidly decrease concentrations of viral particles. Bring in clean outdoor air when appropriate and minimize recirculating air. Direct HVAC airflow to not blow directly from one person to another. And avoid restrictive HVAC filtration upgrades, which significantly reduce airflow that could otherwise disperse virus particles. 
        3. Add True HEPA (H13) Air Purifiers: Supplement general ventilation with airborne infection controls such as portable True HEPA filtration. Choose an effective purifier that’s able to draw in contaminated air and circulate pure air throughout your entire breathing space or 'box' quietly enough not to disturb the class.  

          UV MYTHS: Why Some HVAC Improvements Aren’t a Silver Bullet 

          A myth making the rounds is that installing HVAC (Heating Ventilation and Air Conditioning) improvements alone—such UV bulbs—can make indoor spaces safe. 

          • Many UV (ultraviolet) light applications are unproven for clearing the full volume of air in every room. While massive, powerful lighting arrays pointed directly into a space (as in hospital operating rooms) will work, the effectiveness of adding UV to HVAC ducts is unproven outside the condenser core and plenum. Further, the physics of how air moves through HVAC systems suggests that virus particle concentrations or clouds may not be exposed to enough UV light due to a “shadow effect” from larger particles like dust. 

          THE BOTTOM LINE 

          Alen’s vision is to inspire a healthier life and provide peace of mind for everyone through clean and safe air. That means ensuring our invaluable learning environments are free of harmful particles—from pathogens to allergens to pollutants. 

          Our top-rated line of True HEPA (H13) air purifiers is backed by an exclusive lifetime warranty and an in-house team of air quality experts who can help you quickly build protective solutions for spaces of any size. 

          For more information, visit our Alen for Schools page, call 855.200.5483, or email our dedicated EduSafety team edusafety@alen.com

          IMPORTANT: Alen does not provide medical advice. Consult your doctor or a medical professional with healthcare questions. 


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