How To Choose An Air Purifier?

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Winters in North India are not just cold, they are notoriously polluted too. The smoke from crackers and stubble burning along with fog results in smog that triggers all sorts of respiratory ailments in young and old alike. So, it is no wonder that air purifier sales peak during the winters. But how do you choose the one apt for your needs? What are the factors you need to keep in mind while choosing an air purifier? Let us explore in detail.

Who Needs An Air Purifier?

Contrary to popular belief, air pollution is higher indoors due to formaldehyde emissions from furniture, emissions from cleaning solutions, cooking etc. If your house doesn’t have good ventilation, it could aggravate the situation too.

An air purifier is a necessity if you fall into any of the following categories-

  • If you or any of your family members suffer from respiratory ailments like asthma or allergies.
  • If you live in highly polluted cities like New Delhi, Gurgaon, Ghaziabad, Noida, Bhiwadi, Faridabad etc.
  • If you have a pet,
  • If your home or office is located in an industrial area or in the middle of the city surrounded by vehicles or construction zones.

How Does An Air Purifier Work?

An air purifier has a rather simple mechanism. The fan inside the air purifier sucks in contaminated air through the vents. This air passes through layers of purification and gets pushed out through another set of air vents. The two filters it passes through are a HEPA filter that captures particulate matter and an activated carbon filter to capture any odours. We shall look into them in detail later on.

Factors To Consider When Buying An Air Purifier

HEPA Filter

how to choose air purifier- hepa filter grade
Old vs new HEPA filter

HEPA refers to High-Efficiency Particulate Arresting or High-Efficiency Particulate Air. These filters are made of polypropylene, fibreglass or borosilicate glass fibre.

They can capture up to 99.99% of impurities of size larger than 0.3 microns, depending on the grade of filter used. The grade of the HEPA filter is very important because it determines its efficiency.

An H11 grade HEPA filter captures just 95% of particulate matter larger than 0.3 microns, while an H14 grade filter captures as high as 99.995% of particulate matter. A trade-off, however, is that other things being the same, the air flow rate reduces as the grade of the filter increases.

HEPA GradePurification Efficiency

Activated Carbon Filter

HEPA filters can capture particulate matter like dust, pollens, certain virus and bacteria. But, they are indifferent to volatile compounds in the air which cause odour. To capture these compounds, air purifiers use activated carbon filters.

Activated carbon is made by heating up sources of carbon like coconut shells to a high temperature without air and then exposing it to steam to create minute cracks/ pores. These pores increase the surface area of activated carbon dramatically. They measure 0.002 microns and can adsorb compounds that cause smells.

Unfortunately, most manufacturers don’t provide any specs or details of the activated carbon filter used in the air purifiers. Hence, making a side-by-side comparison isn’t possible.

Related reading: How To Choose A Water Purifier?


how to choose air purifier

CADR refers to Clean Air Delivery Rate. It indicates the volume of air cleaned in an hour and is measured as m3/hr.

CADR is the value that you need to consider to understand whether the air purifier is apt for the given space. You can calculate the volume of air in a given room by multiplying the square footage by 9 ( 9ft is usually the height of most Indian homes). This value divided by the CADR will help you understand how many times the air purifier cleans the air in the room. This brings us to the next point ACH ( Air Change Per Hour).


ACH helps us understand how many times the air in a room changes. If it is too low, the air remains stagnant and unpurified for a long time. So, the purification process wouldn’t be really efficient.

According to AHAM ( Association of Home Appliances Manufacturers), ACH should be at least 3. AHAM Verified air purifiers have an ACH of 4.8.

To check the ACH of the air purifier you have chosen, you can use this calculator and input the CADR of the air purifier in m3/hr and the square footage area of the space you intend to use the air purifier in.

Ease of Operation

ease of operations is a factor to consider on how to choose air purifiers
Controlling air purifier with mobile app

Ease of operation refers to accessibility while using and access to information.

Certain air purifier models from Dyson, Mi, Philips etc come with either remote control or an app through which you can control the settings. This becomes helpful especially at night as you can adjust the airflow without having to move from the bed and disturbing your sleep.

Also, many models have an in-built PM monitor which helps you understand whether the air surrounding is polluted or under favourable levels. This helps adjust the speed of the air purifier accordingly.

Cost of Filters

If you use the air purifier on a regular basis, you will have to change the HEPA and activated charcoal filter every 9-12 months. So, it is important to take a look at the availability and cost of the filters before buying an air purifier.

Generally, they cost anywhere from Rs. 3000 to 7000 depending on the model and the brand. Sharp for example has an air purifier with a mosquito catcher. It is a sticky sheet which needs to be changed every month and costs about Rs. 1000. Such air purifiers have an even higher cost of ownership in the long run.

Mid-segment options come with an indicator alerting you when it is time to change the filters. But higher-end options like Dyson show the extent of usage in the app.

Also, it is highly recommended to buy air purifiers only from known and reputed brands because they guarantee a supply of air filters for years to come- something you can’t expect from fly-by-night operators.


Being an expensive appliance, and a necessary one, most people shift it around the house according to their needs. Hence, it is important to have an option that is portable. Check the weight of the model and also whether the model has a handle so that you can move it around easily.


Certain air purifiers have an in-built ionizer which discharges negative ions. These ions attach to the airborne impurities and settle down, making them easier for the HEPA filter to capture.

But, air purifiers with ionizers have a huge disadvantage. In the process of discharging negative ions, ozone is produced. And ozone is a known lung irritant that can trigger asthma attacks. Hence, it is in your best interest to not opt for air purifiers with ionizers.

Sharp Plasmaculture however is an exception, as it is certified to not produce ozone in its process.

Highly Rated Air Purifiers

Based on user reviews, here are some of the top air purifiers you could consider for your home or office.

Dyson Pure Cool Link Air Purifier

Coway Professional Air Purifier ( Airmega)

Mi Air Purifier 3 

Philips AC2887/20 Air Purifier 

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