# How to Choose a Classroom Air Purifier [Step-by-Step Guide]

Air purifiers are proven tools to reduce COVID-19 spread in the classroom. But choosing which air purifier is best for a classroom can seem complicated. In this article, we take you step-by-step on how to choose the best COVID-19 fighting air purifier for schools and in the classroom.

### Step 1: Measure Size (Volume) of Classroom

Before choosing an air purifier for a classroom, we need to know how much air the purifier needs to clean.

First, measure the area of the classroom floor in square feet or square meters. Next, multiply this number by the height of the classroom to get the total volume. If the number calculated is in cubic feet, divide this number by 35 to get the volume of the classroom in cubic meters.

### Step 2: Calculate the CADR Needed to Clean the Classroom

Next, we need to calculate how much “power” is needed from an air purifier to clean the volume of air calculated in step 1. The amount of air an air purifier is able to clean is given by its CADR rating. The higher a CADR rating, the more air the air purifier can clean per hour.

To do this, we first need to multiply the volume of the classroom by 5. The number after multiplying the volume of the classroom (in meters cubed) by 5 is the CADR needed (cubic meters per hour) from a purifier to clean the classroom.

The reason we multiply by 5 is schools should aim to have all the air in a classroom cleaned and replaced with new air at least 5 times per hour. Therefore, we need to find an air purifier that is powerful enough of cleaning this much air.

### Step 3: Find HEPA Air Purifier(s) with a CADR at or Above Number Calculated in Step 2

CADR ratings are given in two measurements, either cubic meters per hour (CMH) or cubic feet per minute (CFM). The CADR needed for the classroom calculated above is in cubic meters per hour (CMH).

Note: If only the CFM is given, this can be converted to CMH by multiplying by 1.7.

The CADR of powerful air purifiers typically ranges from 500-900 m3/hour. If the CADR needed is over this number, multiple air purifiers may be needed.

Be aware, these ratings are for the purifier’s highest setting. Many air purifiers’ highest settings can be quite loud and disturb the classroom (see step 6).

### Step 4: Choose HEPA Filter Air Purifier, Avoid Purifiers With Add-ons

The best type of air purifier for schools to use to protect students against COVID-19 in the classroom is a HEPA filter air purifier. HEPA filter air purifiers are highly effective at filtering out particles the same size as COVID-19.

When choosing an air purifier for the classroom, avoid extra add-ons such as UV-lights and ionizers. These add-ons increase cost and may pose an additional health risk for students or teachers when operating in school classrooms.

Read More: Schools: Don’t Use This Air Purifier for COVID-19 Protection

### Step 5: Consider Cost/Lifespan of Replacement Filters

The cost and lifespan of a HEPA filter should be considered in addition to the upfront cost of the purifier. Many air purifier companies are not transparent with HEPA filter replacement recommendations and how they calculate the numbers. But roughly calculating the yearly cost of HEPA replacements can help you compare the operating costs of different air purifiers.

### Step 6: Consider Noise Level

Many air purifiers can get loud on high settings. It is important to have an air purifier in the classroom that is not a disturbance. You can find how loud an air purifier is by checking its noise level measured in dB. Anything over 60 dB will very likely be a disturbance in the classroom.

Make sure to check the air purifier’s noise level on high, as some air purifier companies market noise levels on lower settings, which is misleading.

Read More: FAQ on Classroom Air Purifiers

## Real-World Example: Choosing an Air Purifier for a Classroom

Let’s go through the process of finding an air purifier for a 30 by 30 feet (9.1 by 9.1 meter) classroom with 9-foot (2.7 meter) ceilings.

Step 1 is to calculate the volume of the classroom in meters: 9.1 x 9.1 x 2.7=223 cubed meters.

Step 2 is to multiply the volume by 5: 223 cubed meters x 5=1115. The CADR of the purifier needed for the classroom should be at least 1115 m3/hr.

Step 3 is to find an air purifier with a CADR close to 1115 m3/hr. Since most air purifiers do not have a CADR rating of this high, a combination of two air purifiers could be the best solution.

Note, if the CADR rating uses CFM like the air purifiers below, multiply this number by 1.7 to get the CADR in m3/hr.

From the Smart Air product line, one Blast air purifier with CADR of 890 m3/hr would get close to this 1115 m3/hr number. Adding an additional smaller air purifier to the classroom such as the Sqair would get the total air purifier CADR to over the 1115 m3/hr number.

Steps 4,5,6: Lastly, make sure the air purifier uses HEPA filters without other gimmicky technology, take note of filter replacement costs, and ensure the purifier has acceptable sound levels (over 60 dB is likely too noisy for most classrooms).

### How Smart Air Protects Students & Teachers in Schools

Smart Air is a certified B Corp and social enterprise committed to helping people breathe clean air. Smart Air’s no-nonsense Blast & Blast Mini air purifiers are used in schools all across the globe. A few schools include the University of Chicago and the American Embassy School. Smart Air’s purifiers remove the same particles as the big companies for a fraction of the cost.

Smart Air’s powerful Blast air purifier has a high airflow and can clean classrooms and school halls up to 130 sqm (1400 sqft) in size. It’s also ideal for the classroom being one of the quietest purifiers on the market. When run on low, its quiet mode can clean classrooms up to 60 sqm (650 sqft) without disturbing classroom lessons. Many classrooms even run the Blast on high with minimal disruption to the classroom.

### Free Guide to Breathing Safe

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Smart Air is a social enterprise and certified B-Corp that offers simple, no-nonsense air purifiers and provides free education to protect people from the harms of air pollution. We are proud to be the only certified B-Corp dedicated to fighting air pollution.