# How to Choose an Office Air Purifier [Step-by-Step Guide]

Air purifiers in the office are important tools to limit COVID-19 spread. But choosing which air purifier is best for an office can seem complicated. In this article, we take you step-by-step in how to choose the best COVID-19 fighting air purifier for offices.

## Six Steps to Choosing an Air Purifier for the Office

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

Before choosing an air purifier for an office, we need to know how much air needs to be cleaned.

Measure the area of the office floor in square feet or meters. Next, multiply this number by the height of the office to get the total volume. If the number is in cubic feet, divide this number by 35 to get the size of the office in cubic meters.

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

Next, we need to calculate how much “power” we need from an air purifier. The amount of air an air purifier is able to clean in a given period of time is 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 office by 2. The result is the CADR needed (cubic meters per hour) from a purifier to clean the office.

The reason we multiply by 2 is ASHRAE recommends air in offices should be cleaned and replaced with new air 2-3 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 office calculated above is in cubic meters per hour (CMH), so this is the number we need to pay attention to.

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.

These ratings are for the purifier’s highest setting. Many air purifiers’ highest settings can be quite loud and disturb the office (see step 6).

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

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

Medical-grade air purifiers” are not needed and are more often than not a marketing gimmick.

When choosing an air purifier for the office, avoid extra add-ons such as UV-lights and ionizers. These add-ons increase cost and may pose an additional health risk for office workers.

Read More: Don’t Use These Air Purifiers in the Office

### 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. Take note that 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 office that is not a disturbance. You can find how loud an air purifier is by checking its noise level (given in dB). At Smart Air, we recommend air purifiers with a top sound of close to 50 dB. Anything above 60 dB is likely to be a disturbance in the office.

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 Office Air Purifiers

## Real-World Example: Choosing an Air Purifier for an Office

Let’s go through the process of finding an air purifier for a 45 by 45 feet (13.7 by 13.7 meter) office with 9-foot (2.7 meter) ceilings.

Step 1 is to calculate the volume of the office in meters: 13.7 x 13.7 x 2.7=507 cubed meters.

Step 2 is to multiply the volume by 2: 507 cubed meters x 2=1014. The purifier needed for the office should be at least 1014 m3/hr.

Step 3 is to find an air purifier with a CADR close to 1014 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 1014 m3/hr number. Adding an additional smaller air purifier such as the Sqair would get the total air purifier CADR to over the 1014 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 offices).

### How Smart Air Protects Offices Around the World

Smart Air is a certified B Corp and social enterprise committed to making offices safe. Smart Air’s no-nonsense Blast & Blast Mini air purifiers are used in offices all across the globe. Offices that use Smart Air purifiers include the BBC, Ford, Zomato, and many more.

Smart Air’s powerful Blast HEPA air purifier has a high airflow and can clean offices up to 130 sqm (1400 sqft) in size. It’s also ideal for offices because it is one of the quietest purifiers on the market.