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Choosing a commercial air purifier

COVID-19 has put the burden of clean air on hospitals and schools around the globe, as well as other commercial establishments such as dental surgeries, gyms, offices etc. In any indoor setting, fresh air is key to diluting the air and high CO2 levels is a good indicator for when more ventilation is required.

Fresh air should always be available either through open windows/doors or through your mechanical HVAC system (check this uses fresh air rather than recirculated air). When CO2 levels are high, open the windows or turn up the HVAC system - this will dilute smaller airborne particles that can hover in the air for several hours.

"A ventilation policy is NOT the same thing as an Indoor Air Quality Strategy"

Indoor Air Quality

Although CO2 is an important part of Indoor Air Quality (IAQ), it is NOT the primary consideration. If you are not also monitoring particulates or chemicals in the air, how will you know if you are providing a healthy environment for your employees?

An HVAC system will provide fresh air for ventilation, but will most likely not purify the air without an expensive upgrade.

Windows or an HVAC system will help you meet your ventilation targets but an air purifier helps you meet your IAQ targets. Choose a good commercial purifier suitable for your room size and the speed you are likely to run it at. Don't just monitor CO2 levels. An air quality monitor that also has sensors for Particles and Total Volatile Organic Compounds (TVOCs) will give you a full understanding of your indoor air quality.

So in terms of looking after your customers, employees, pupils, here are some tips to help you choose the right commercial air purifier:

What to look for in a commercial air purifier

HEPA filter

All HEPA filters can trap particle pollution including viruses and nanoparticles. Some purifiers are marketed as being able to capture smaller than PM0.3 but you don't need patented technology for this. Our short video will hopefully dispel any myths around PM0.3.

The higher the grade HEPA, the more resistance to airflow so your purifier should have a powerful fan. If the purifier has a high grade HEPA but average airflow, it may be more suitable in a room with less pollution.

Carbon filter

Add a carbon filter to clear the air of gases and chemicals - also known as volatile organic compounds (VOCs). If you are close to a busy road, wood-burning or factories, you might be concerned about chemicals in the air as it will find a way indoors even with the windows closed. You will also have chemicals in the air if your room has been newly painted, has new furnishing/flooring or if you use chemical cleaners.

In these cases, opt for a purifier that has a carbon filter with granulated activated charcoal rather than a light smattering on fabric. The inclusion of a carbon filter will create additional resistance to airflow so your purifier should have a powerful fan.


A pre-filter protects the HEPA filter from larger particles such as dust and hair, and in doing so, prolongs the life of your HEPA filter. The great thing about pre-filters is they can be washed and cleaned periodically, unlike HEPA filters. But because they add an extra layer of resistance to your air purifier, they can reduce airflow and increase noise so won't work with all purifiers. After running numerous tests, it decreases the performance of the Sqair but our commercial purifiers, with large centrifugal fans, are stronger so a pre-filter doesn’t affect airflow as much.

Forget the hype

Don’t be fooled by the marketing hype for for medical grade purifiers - there is no standard. Most companies don’t sell to hospitals, but use this name to make their purifier sound fancy. Also check the claims of purifiers using UV lights (few are strong enough to be effective at all) and ionisers (which emit ozone).

Check the Clean Air Delivery Rate (CADR)

You just need two measurements to work out the volume of clean air your purifier will deliver - 1) the dimension of the room you wish to use it in; and 2) the CADR which the manufacturer provides. Our calculator takes the cost of the purifier, your room dimension and the CADR to calculate the true cost of clean air. Works for any air purifier so do your research before purchasing a purifier.

Work out the number of Air Change per Hour (ACH)

The ACH tells you the number of times each hour that the air in a room is replaced with completely clean air. For example, a value of ‘5’ ACH means a room’s entire volume of air is replaced with clean air 5 times in one hour. Most schools will typically have 1.5 ACH with the windows closed. Check out our online ACH calculator to work out how many air changes you will get from any purifier.


Most companies provide the CADR and airflow on high settings only. Our experience shows that purifiers are generally run on low or medium setting due to the noise levels. Schools tend to favour a maximum decibel level of around 50dB in order to be able to hear a class over over the running noise of an air purifier. When researching air purifiers, check the CADR and the noise levels on all speeds. If the information isn't published, ask the manufacturer.

Using an air purifier with the windows open

If your ventilation strategy includes always opening windows and/or you are worried about the outdoor pollution levels, our tests show our air purifiers are still effective with the windows open.

Impact of good IAQ in offices

If you are not considering an air purifier for COVID, then consider the impact of clean air on productivity:

  • A study of a call centre with 4900 employees found that when the air quality index (AQI) increased by 10 points, employees answered 0.35% fewer calls. On days where the air quality index was hazardous, the call centres handled about 20,000 fewer calls.

  • In a study at a German stock exchange, it was found that a 12ug/m3increase in PM10 decreased the probability that stock traders would log into their computers and trade stocks by 10%. Read more...

  • In September 2021, a one year study on 300+ office workers aged 18-65 in 42 buildings across India, China, UK, USA, Mexico & Thailand concluded that poor indoor air quality in an office environment can significantly impact concentration, accuracy and response times of employees. It also found that PM2.5 levels indoors result from a combination of indoor and outdoor sources but found that typical indoor sources (dust, smoking, cooking, cleaning products) are less prevalent in office buildings than other building types (Patel et al 2020). PM2.5 of outdoor origin penetrates indoors through ventilation, infiltration, and filtration - Read more...

Impact of good IAQ in schools

  • 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. Read more...

  • 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. Read more...

Designing a commercial air purifier

From its humble beginnings as a supplier of DIY purifier components, Smart Air has used years of experience, testing and data to create 2 commercial purifiers.

Meet the Blast and Blast Mini

The Blast units have been stripped down to the essential features - a super fat HEPA filter and a crazy powerful fan. How fat is 'super fat'? The Blast Mini has an impressive area of 11m2 when open. So how does this simplicity translate into real life effectiveness? Well see for yourself...

We have tried to keep the prices affordable and as far as we can see, our commercial purifiers are top of the range in terms of clean air delivery and noise levels. It is also cheaper than other purifiers in the same class.


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