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Choosing the right air purifier

February 14, 2022, 20:10 GMT+1
Read in about 5 minutes
  • Clean, fresh air in classrooms is more important than ever, says Edward Ballsdon
Choosing the right air purifier

Clean air has never been more important, whether delivered via ventilation or air purification.

But with so many products on the market, how does your educational establishment choose the right one for your needs?

As the world emerges from lockdown and there are more gathering indoors, the threat of airborne transmission escalates.

There is evidence to suggest that, after a protracted period of social distancing and mask wearing, people have weaker immune systems to defend themselves against the onslaught of respiratory viruses such as flu and the common cold, as well as Covid-19 and its variants.

Schools are rightly concerned about protecting their students and teachers. As a by-product of that protection, they also want to reduce absenteeism and boost learning. 

Many buildings struggle to achieve the World Health Organization’s recommended air change rate of 10 litres per second per person.

Opening windows is not viable in winter. That’s where air purification comes in, either working in isolation (single or multiple units) or to supplement an in-built Heating, Ventilation and Air Conditioning (HVAC) system. 


When it comes to capital cost, compare like with like. You get what you pay for. Compare the cost against that of installing a new integrated HVAC system. Also think about ongoing costs.

Air purification units consume the equivalent of a fridge freezer and cost just a few cents a day to run. Further substantial savings can be made on energy (and associated carbon emissions) from not having to heat fresh air intake.

With energy cost currently very high, the ongoing savings can quickly offset the initial capital cost of the air purifiers.

SAGE encourages buyers of air purifiers to exercise caution and do their homework. 

For a relatively small investment, and low ongoing costs, your school can achieve a high standard of indoor air quality.

Portable, hospital-grade air purifiers also offer flexibility, as they can easily be moved around to heavily occupied rooms or to areas where enhanced aerosol generation is likely, e.g. singing, projected speech or aerobic activity.

Choosing wisely can serve as a twenty-four seven bodyguard to protect and enhance the lives of students and teachers alike.

Five things to consider when buying an air purifier

  • Technology
  • It’s critical to choose the right technology for the job. In its Covid-19 air cleaning guidance, the UK SAGE committee’s environmental and modelling group recommends High Efficiency Particulate Air (HEPA) filtration systems to capture COVID-19 particles, with germicidal ultraviolet light (UVC) as a supplemental treatment to inactivate the virus. HEPA is even proven by NASA to trap a minimum of 99.97% of fine particulate matter.
  • Strong airflow
  • Portable air purifiers must be heavy duty, with a powered fan system. This creates high static air pressure, which is necessary to allow sufficient air to flow through the HEPA filter and to boost air cleaning performance throughout an entire space, rather than just the air around the purifier machine itself. Residential air purifiers using HEPA will not serve as a substitute for a hospital grade device containing a powerful fan. 
  • Harmful side effects
  • These are associated with the kind of air purifiers sometimes referred to as using ‘additive’ technologies (based on indirect chemical reaction) as opposed to ‘subtractive’ (filtering and direct inactivation). Avoid UVA/UVB, ionisation, plasma, electrostatic precipitation and oxidation methods. These have limited evidence of efficacy against the virus and/or significant concerns over toxicological risks during application. This guidance comes from the SAGE committee.
  • Reputation
  • Be aware that the big brands generally make small devices for residential use only, not fit for purpose in a school environment. Marketing claims can be exaggerated and unsubstantiated. The key is to look for independent scientific testing carried out in real life environments from respected laboratories and institutions to validate any claims. Look for case studies in other schools and contact a couple of quoted customers to obtain a first hand account of their experience. Check the manufacturer’s sustainability credentials, especially the potential to recycle both the product itself and the consumables. 

Edward Ballsdon, co-founder and managing director, Rensair.