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Start with your room
A purifier cleans the air in one closed room. It does not clean a whole flat, and it does little with the windows open. So before you compare brands, measure the room you use most.
You need three numbers: length, width and ceiling height. Many Indian homes have ceilings of about 10 feet.
What CADR means
CADR stands for clean air delivery rate. It tells you how much clean air the machine gives out each hour, usually in m³/hr.
Multiply the room's length, width and height in feet, then divide by 35 to get cubic metres. Multiply that by 5. This gives you a CADR for five air changes an hour.
Five is our example target, not an official standard.
| Room size | Volume at 10 ft ceiling | CADR for 5 changes an hour |
|---|---|---|
| 120 sq ft | 34 m³ | About 170 m³/hr |
| 180 sq ft | 51 m³ | About 255 m³/hr |
| 250 sq ft | 71 m³ | About 355 m³/hr |
| 350 sq ft | 99 m³ | About 495 m³/hr |
Be careful with "covers X sq ft"
Coverage figures depend on how many air changes a brand assumes, and they are not always worked out the same way. Look at two listings in the table below. One gives 360 m³/hr with 462 sq ft. The other gives 230 m³/hr with 400 sq ft. The ratio is quite different, so do not compare on square feet alone.
Compare CADR, and check two more things:
- What was it measured for? CADR can differ for smoke, dust and pollen. Smoke is the closest to fine pollution particles.
- Who measured it? A test standard or a named lab tells you more than a bare number.
HEPA, in plain words
A HEPA filter is a dense paper-like sheet that traps very fine particles. That includes the PM2.5 you see in AQI reports. Most purifiers stack three layers.
| Layer | What it does | What to check |
|---|---|---|
| Pre-filter | Catches hair and big dust | Can you clean it yourself? |
| HEPA | Traps fine particles | Is the grade named, such as H13? |
| Activated carbon | Takes up some smells | How much carbon is there? |
Words like "HEPA-type" or "HEPA-style" do not mean the same as a named grade. Percentage claims mean little unless the listing says what particle size was tested, under which standard, and by whom.
If a model has an ioniser, check whether it can be switched off, and whether the maker says it produces ozone.
Top 5 air purifiers to look at
We have not tested these. The details come from each Amazon listing, and the pros and cons are our reading of those details and of this type of product. This is a shortlist, not a ranking. We picked popular listings on Amazon.in, so the order does not mean one is better. Check the current price, CADR, filter cost and reviews on Amazon.
| Product | Type | Listed detail |
|---|---|---|
| Coway Airmega 150 | True HEPA | Covers 355 sq ft |
| Philips AC0950 | Smart | Wi-Fi |
| Xiaomi Air Purifier 4 Lite | CADR listed | 360 m³/hr, covers 462 sq ft |
| Honeywell 3-in-1 | Three layers | Pre, H13 HEPA, activated carbon |
| Mijia by Xiaomi 4 Compact | CADR listed | 230 m³/hr, covers 400 sq ft |
1. Coway Airmega 150
This is a three-stage purifier with an air quality sensor and an auto mode. It stands out for its long listed filter life. It is aimed at a buyer who wants fewer filter changes in one main room.
Key details
- Filters: pre-filter, carbon filter and True HEPA filter, listed as class H13
- Coverage: listed as up to 355 sq ft
- Filter life: listed as 8,500 hours
- Power and noise: 35 watts, listed as 22 decibels
- Controls: touch panel, auto mode and a 4 colour air quality lamp
- Warranty: 7 years on the motor, 1 year on electrical parts
- It is the only listing here with filter life in hours, which helps you work out filter cost
- Auto mode changes the fan speed using the air quality sensor
- One-touch filter removal is listed for easy changes
- CADR not listed, so you cannot check it against your room with the sum above
- No Wi-Fi or app listed
- The 22 decibel figure does not say at which speed
Good for: One main room where you want fewer filter changes and do not need an app.
2. Philips AC0950
This is a small smart purifier that you run over Wi-Fi from the Air+ app. It has the lowest listed wattage of the five. It is aimed at a buyer who wants to control a bedroom purifier from a phone.
Key details
- Filters: pre-filter, HEPA NanoProtect and active carbon
- CADR: listed as 250 m³/hr
- Power: 23 watts
- Noise: listed as 20.5 decibels in sleep mode, and 49.5 in the details
- Controls: app, touch, Alexa, Google Assistant, auto mode and child lock
- Size and weight: 23.8 x 24 x 36.4 cm, 2.7 kg
- The app shows PM2.5 levels, changes fan speed and gives filter alerts
- At 23 watts it has the lowest listed power here
- Auto mode changes the fan speed for you
- Coverage is given as 300, 320 and 700 sq ft in different places, so go by CADR, which is about 175 sq ft on our example
- Warranty not listed, so confirm it
- Filter life in hours not listed, and you need it to work out the yearly filter cost
Good for: A small to medium bedroom where you want to run the purifier from your phone.
3. Xiaomi Air Purifier 4 Lite
This purifier has the highest listed CADR of the five, and a display for AQI, temperature and humidity. It is aimed at a buyer with a medium room who likes readings at a glance.
Key details
- Filters: primary filter, True HEPA and activated carbon
- CADR: listed as up to 360 m³/hr
- Coverage: listed as 462 sq ft
- Power and noise: 33 watts, listed as 32.1 decibels
- Controls: Xiaomi Home app, plus voice through Alexa and Google Assistant
- Warranty: 1 year on the main device, filter not covered
- Its CADR can handle a larger room than the others here
- The display shows AQI, temperature, humidity and Wi-Fi status
- A filter indicator tells you when to change it
- Filter life in hours not listed, so confirm it before you work out the yearly cost
- The warranty lasts one year and leaves out the filter
- On our five air changes example, 360 m³/hr suits about 250 sq ft, less than the 462 sq ft listed
Good for: A medium room of about 250 sq ft, where you want air readings on the machine itself.
4. Honeywell 3-in-1
This is a small purifier with a pre-filter, a named H13 HEPA filter and activated carbon. It is the smallest and lightest of the five, with the lowest listed CADR. It is aimed at a buyer with a small bedroom or office.
Key details
- Filters: pre-filter, H13 HEPA and activated carbon
- CADR: listed as up to 152 m³/hr
- Coverage: listed as up to 235 sq ft at 2 air changes an hour
- Noise: listed as 29 decibels
- Size and weight: 21.5 x 21.5 x 32.2 cm, 1.5 kg
- Controls and warranty: touch control, 2 year maker's warranty
- The H13 grade is named, not just a vague HEPA-type label
- At 1.5 kg it is easy to move between rooms
- The listing says how coverage was worked out, so you can compare it
- On our five air changes example, 152 m³/hr suits about 105 sq ft, far less than the 235 sq ft listed
- No app, auto mode or air quality sensor listed
- Wattage and filter life not listed, so confirm both
Good for: One small bedroom or home office.
5. Mijia by Xiaomi 4 Compact
This is a compact purifier with air intake all the way round and a PM2.5 sensor. It gives more CADR than the Honeywell in a similar size. It is aimed at a bedroom or home office.
Key details
- Filters: three-stage 3-in-1 filter, listed as HEPA
- CADR: listed as 230 m³/hr
- Power and noise: listed as 27 watts at maximum, and 20 decibels in sleep mode
- Controls: Xiaomi Home app, Alexa, Google Assistant, timer and child lock
- Size and warranty: 22 x 22 x 35.5 cm, 2.2 kg, 1 year warranty
- Sleep mode is listed with the display lights off, which helps at night
- Auto mode changes the fan speed using the sensor
- The app adds a timer and child lock
- Coverage is listed as 400, 172 to 291 and 517 sq ft in different places, while our example gives about 160 sq ft
- HEPA grade and filter life in hours not listed
- The box list names no filter, so confirm one is fitted
Good for: A bedroom of about 160 sq ft where you want a sensor and app control.
The real cost: filters
The filter is where the money goes. Before buying, find three things: the filter's price, its rated life in hours, and whether genuine filters are easy to get in India.
Here is a sum using a made-up example: a ₹2,000 filter rated for 4,000 hours. Put in your own model's figures.
| Hours a day | How long a filter lasts | Filter cost a year |
|---|---|---|
| 8 | About 16 months | About ₹1,500 |
| 12 | About 11 months | About ₹2,200 |
| 24 | About 5.5 months | About ₹4,400 |
Rated life is a guide. In a dusty area, or during a bad winter in north India, a filter can clog sooner. Clean the pre-filter as the manual says, because it protects the costlier filter behind it.
What it costs to run
This table uses ₹8 per unit as an example, and 30 days a month. Your rate depends on your state and usage, so check your bill. Purifiers use different wattage at each speed, so check the listed power.
| Power | Hours a day | Units a month | Cost a month |
|---|---|---|---|
| 30 watts | 12 | 10.8 | ₹86.40 |
| 30 watts | 24 | 21.6 | ₹172.80 |
| 50 watts | 12 | 18 | ₹144 |
| 50 watts | 24 | 36 | ₹288 |
Using one in Indian conditions
- Pollution season. In north India, air is often at its worst from late October to February. If you live there, buy before the season, as stock and filters can run short.
- Run hours. Run on high for a while with the door shut, then drop to a quieter speed for the night.
- Noise. Check the sound level at the low speed, since that is what you will hear when you sleep.
- Small flats. One machine serves one room well. Move it with you, or keep the bedroom door shut.
- Power cuts. Check if it restarts by itself. At this wattage, a home inverter can usually run one.
- Monsoon. Damp can make a filter smell. Keep spare filters sealed in a dry place.
Before you buy
Keep doors and windows closed on bad days, and air the room when AQI is lower. It is not a medical device, so ask a doctor about any breathing concern. Then choose the machine whose CADR fits your room and whose filter you can afford to replace every year.
Read next
We read the Amazon listings, compared the details and noted what they leave out. We have not tested these products, and brands do not pay to be listed.
Common questions
What CADR do I need for a bedroom?
For a 120 sq ft room with a 10 foot ceiling, 170 m³/hr gives about five air changes an hour. For 180 sq ft, look at about 255 m³/hr. Five changes is a simple target we use as an example, not an official standard.
How long should I run an air purifier each day?
Run it while you are in the room, with doors and windows closed. In pollution season many people run it through the night in the bedroom. It only cleans the room while it is on.
Can I wash a HEPA filter?
Usually not, unless the maker says it is washable. Water can damage the filter. Many pre-filters can be cleaned, so check the manual.
Does an air purifier remove smells and gases?
A HEPA filter catches particles, not gases. Smells are handled by an activated carbon layer, and how much it does depends on how much carbon there is. Ask the brand before you expect much from a thin layer.