Is Your Air Purifier Right For Your Room Size?

Air Purifiers should ideally change the air in a given area every 15 minutes.

For optimal performance, the CADR value of the air purifier should be roughly around the square foot area of the room.

Diwali is, unfortunately, the time of the year when air pollution spikes. While firecrackers are a massive contributing factor, so is stubble burning in various North Indian states.

We all know that air purifiers can provide a much-needed respite from air pollution. The layers of HEPA and activated carbon filters capture particulate matter larger than 3 microns, VOCs, smoke and other odour. 

But how do we know if the one you choose is sufficient to purify the entire volume of air in a room? How do we know if it is effective? Let us find out.

HEPA Filter

A HEPA filter is the most important component of an air purifier. You may have all sophisticated features like Wi-Fi connectivity, realtime air quality reports and so on. But if your air purifier doesn’t have a high-quality HEPA filter, then it is like having a Mercedez without tyres.

That is why the grade of the HEPA filter is the most important aspect to look at while buying an air purifier. The grade signifies the per cent of PM 2.5 that can be captured by the air purification system.  

H14 grade is considered the best as it has a filtration efficiency of 99.995%.On the other hand, an H10 HEPA Filter captures only 85% of the particulate matter larger than 3 microns.  If not H14, at least get an air purifier with H13 grade HEPA filter. 

While HEPA Filter indicates the efficiency of the purification system, CADR or clean air delivery rate indicates the effectiveness. 

Clean Air Delivery Rate(CADR) and Air Change Per Hour (ACH)

Clean air delivery rate or CADR, as the name suggests, indicates the volume of purified air that the air purifier pushes out into the room. It is typically given in cubic meter per hour ( m3/ hr).

So if you are using your air purifier for a small space, then one with low CADR will be enough. But if you are using it in a large space, you need an air purifier with a high CADR. Let us quantify this aspect so that it helps in your purchase decision.

For that, first, you need to understand what is ACH or air change per hour. Simply put, it is the number of times the air purifier cleans the air in a room. According to the American Society of Heating, Refrigerating and Air-Conditioning Engineer, the air change rate has to be at least 4 for a room where those with respiratory ailments live. This means the entire air needs to be purified every 15 minutes. And you can use this as a reference if you live in a heavily polluted environment like New Delhi.

CADR and Square foot Area

If you want to maintain ACH of 4, the ballpark figure of CADR needed for a given space is almost equal to its square foot area. This is assuming that the height of the ceiling is 9 ft.  

Many manufacturers use ACH of 2 and recommend their air purifiers for a larger space. This may look like an attractive proposition. But in such cases, the purification efficiency will be less than optimal. You could also check for CADR/ ACH calculators to decide what should be the ideal CADR needed for your room. 


Buying an air purifier apt for a given space is important to ensure its effectiveness. Ideally, the CADR value should be equal to the square foot area of the room. And for optimal performance, it is better to use multiple units in larger areas like a conference hall or a huge living area.


Smart Home Guide Team

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