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Air purification in classrooms

Much has been said about the need to ventilate classrooms - elevated CO2 levels are increasingly linked to high indoor viral transmissions rates.

Fresh air dilutes indoor air and helps prevent the spread of coronavirus. Natural ventilation is achieved by opening windows or a fresh air HVAC/mechanical ventilation system.

However, balancing natural ventilation with reasonable temperatures can be a challenge in the colder months. And if the school is located in a polluted neighbourhood, health issues can arise from long-term exposure to outdoor air pollution. This means that a school has to juggle multiple strategies:

  • COVID strategy

    • class bubbles / face masks

    • opening windows vs thermal comfort / noise

    • monitoring CO2

  • Indoor air quality strategy

    • reducing outdoor air pollutants, including traffic fumes, which finds its way inside even with doors and windows closed

    • chemicals in the air from cleaning products, paint, furnishing, furniture, flooring etc

Focusing on one and not the other can impact the health of teachers and pupils so consider installing portable air purifiers to supplement your ventilation strategy.

A good air purifier will yield excellent results

  • In 2015, a big leak at a natural gas facility in the US resulted in the company paying for air filters in every classroom, office and common area in ALL schools within a five mile radius. After 4 months, Math scores went up by 0.20 and English scores by 0.18 standard deviations. These same results could be achieved by cutting class sizes by 1/3rd

  • London School of Economics studied university students’ test performance relative to air pollution levels on the day of the test alone. Results showed that taking a test in a filtered rather than unfiltered room would raise test scores by 0.09 standard deviations

  • Researchers gave 35 healthy Shanghai university students real or fake air purifiers and tracked several health markers for two days. They found that after 48 hours, the students had significantly lower inflammation in their blood vessels. They also had lower blood coagulation (a marker of blood clotting) and less constricted blood veins

  • In 2018, Goose Green became the first state school in London to install air purifiers in every classroom. They have anecdotal evidence of improvements in asthma symptoms and coughing fits

  • 3 schools in Camden had high PM levels, some up to 40 times greater than WHO levels. Air purifiers were installed in all classrooms. Since installation, staff noticed a decrease in sick absence amongst both children and teachers

How should I choose an air purifier for a classroom?

Choose an air purifier with HEPA filters. All HEPA filters are highly effective at filtering out nanoparticles, including coronavirus. The HEPA grading system relates to PM0.3 which is the smallest size particle that travels in a straight line. This makes it the hardest size to capture, NOT the smallest size. In fact, smaller particles travel in a zig zag motion which means, according to NASA, virtually 100% of nanoparticles will be trapped in the filter.

A Carbon filter will capture chemicals and gases from the air. Only a carbon filter can get rid of fumes from traffic, odours, smoke and Volatile Organic Compounds (VOCs). If your school is in a polluted neighbourhood, be sure to get a purifier with both HEPA and Carbon filters. Our video below shows you how well our purifiers clean the air of smoke.

Choose the best purifier for your class size. Schools should be aiming for at least 5 air changes per hour. To see if a purifier can achieve this, you need two figures: the Clean Air (CADR) ratings of the purifier; and your classroom size. Although CADR has its flaws, it is the only way to do a like for like comparison. Once you have these two figures, our handy calculator will show you how much CADR you will need to achieve 5 air changes. If you have any trouble using our calculator, just drop us a line at

Check the noise levels. It is very likely that you will run the air purifier on the lowest setting so it doesn't disturb the class. Before purchasing your purifier, be sure to check how much clean air (CADR) you actually get on the lowest speed. We provide the CADR for all three speeds allowing you to calculate exactly how effective our purifiers will be at cleaning your classroom on the quietest setting.

Our cost-effective commercial purifiers are perfect for schools. All purifiers are boxes with a fan and a filter inside, but the basic design of the commercial Blast purifiers means more space for a bigger fan and a much bigger HEPA. In terms of the Clean Air Delivery Rate, our Blast Mini churns out the same amount of clean air as 2.2 Blueair 203 purifiers!

See how quickly our purifiers can clear the air of smoke...

All HEPA purifiers will clean the air but why settle for 2-3 air changes an hour when you can have 5+ for the same money? In an unregulated industry, research and a basic knowledge of indoor air quality is essential.


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