Buying an air purifier for your school? Here’s what you need to know.

Is your school preparing its indoor air quality improvement plan? If you answered yes, then you probably have started looking at all the different air purifiers out there—and there are a lot! At one end of the spectrum, there are units suitable for industrial or healthcare settings and at the other, those for home-use. This leaves school air purification somewhere in the middle due to the size of a classroom and number of people in it. In this post, we’re going to cover off a few things to help you make an informed decision as you evaluate your options.

Images: (left) PuraShield unit for industrial use is around $6,600 USD and 58” high, (middle) Copernicus’ True HEPA Air Purifier $820.96 USD and 22” high, (right) Bissell My Air is around $100 USD and 12 ¼” high.

If you have ever felt like taking a snooze during one of those marathon departmental meetings, it could be partly due to the meeting topic, but it could also have something to do with the air quality in the room. Air purification is a key component in improving air quality indoors whether it is a meeting space or a classroom. There are many benefits to having good air quality in a classroom including increased student engagement, improved well-being for allergy and asthma sufferers and reducing the transmission of viruses, including COVID-19. The virus spreads through aerosolized particles that tend to hang in the air unless they are blown away or removed; air purifiers can do both.

CADR: Clean air delivery rate

This measurement refers to how many cubic feet of air is purified per minute (CFM) through an air purifier’s filters. Look for a unit that is the right capacity for a classroom (more than 300 CFM). Undersized home-use units are not suitable for a typical classroom because of the size of the room and how many people are in it, and large industrial units are too large and loud.

ACH: Air changes per hour

A study at Harvard’s T.H. Chan School of Public Health recommends 5-6 air changes per hour for an “excellent” air quality rating. Air changes per hour can be increased by opening windows and doors as well as using air purifiers. However, for open windows and doors to be effective, they need to provide a cross breeze to circulate the air in the room. Unfortunately, many schools do not have windows that open.

True HEPA: High Efficiency Particulate Air

Although there are units available with multi-stage air purification using ozone, ionizing and UV-C light, the majority of the air purification process is done through the filters. True HEPA filters have been tested and certified to capture at least 99.97% of small particles measuring 0.3 microns, like viruses. If you see a Minimum Efficiency Reporting Value (MERV) rating without the term True HEPA, they are probably not referring to True HEPA filters. MERV is a very broad reporting value.

Ozone

Ozone molecules are the main component in smog. It is considered an air pollutant by the United States Environmental Protection Agency (EPA) and can irritate the lungs. So you might be wondering if it is so dangerous, why would anyone use ozone to purify the air indoors? Ozone is highly reactive and can change the chemical composition of some substances in the air, which forms the basis of claims that it purifies the air. Some states, like California, have banned air purifiers that use ozone. Ensure you understand the safety regulations in your area before selecting a unit.

Ionizing

Some units tout the effectiveness of ionizing, but ionizing charges particles so they attach to nearby surfaces (which then need to be cleaned), versus removing them from the environment entirely. Wiping down all the surfaces in a classroom several times a day is not feasible.

UV-C Light

Another controversial function is using UV-C light to clean the air. In most air purifiers, the particles are not in the unit long enough for UV-C light to do its job. Some units use UV-C light on the captured particles in the filters. This additional sanitizing is not neccessary because the filters have already removed the particles from the air.