Delhi's air turns in the last week of October and stays bad until about the end of January. That's not a forecast, it's what happens every year, and it's the window an air purifier has to earn its keep in.
Start with the number that frames everything. Delhi averaged 99.6 µg/m³ of PM2.5 across the whole of 2025, which made it the most polluted capital city in the world for the seventh time in eight years, according to the IQAir World Air Quality Report. The WHO guideline is 5 µg/m³ a year. We live at roughly twenty times that, as a baseline, every year. On the worst day last November the daily average ran close to 460.
Most guides to the best air purifiers for Delhi pollution hand you five products and five bullet lists. That doesn't help you much, because what decides whether a HEPA air purifier works in your room isn't the brand. It's one number, and the box usually prints a different one.
What size air purifier do I need for my room?
Multiply your room's area in square feet by 1.13. That's the minimum CADR in m³/h you should buy. A 120 sq ft bedroom needs about 136 m³/h. A 252 sq ft drawing room needs about 285 m³/h. Here's where that comes from.
CADR stands for Clean Air Delivery Rate. It's the volume of clean air a machine puts out per hour, and it's the only spec that tells you how fast your room gets cleaned. India quotes it in m³/h. The United States quotes it in CFM. That mismatch is where most of the money in this category gets wasted.
The sizing rule comes from AHAM, the American Home Appliance Manufacturers association, and ENERGY STAR uses the same one. Multiply your room's square footage by two thirds to get the minimum CADR in CFM. That gives you about 4.8 air changes an hour, which is what indoor air specialists recommend when somebody in the house has allergies or asthma (Smart Air, HouseFresh). In a Delhi winter, treat 4.8 as your floor, not your target. Convert with 1 CFM = 1.7 m³/h and the whole thing becomes one step.
Minimum CADR (m³/h) = room in sq ft × 1.13
Or the other way round: room a machine really covers (sq ft) = its CADR ÷ 1.13
Two things to watch. If your ceilings are higher than 8 feet, and plenty of older Delhi construction runs 10 to 11 feet, add about 25% for a 10 foot ceiling. And if the door stays open to the rest of the flat, you're not purifying that room any more, you're purifying the flat. So size for the flat, or shut the door.
Why does the coverage on the box not match?
Because manufacturers quote coverage at roughly 1.5 to 3 air changes an hour, not the 4.8 that clears smog. Read every coverage claim, on any brand, as two to three times what it will give you here. These are three models we stock, using only the figures the manufacturers publish themselves.
| Model | Published CADR | Coverage claimed | Implied air changes | Coverage at 4.8 ACH |
|---|---|---|---|---|
| Philips AC0951 | 250 m³/h | 65 m² (700 sq ft) | 1.6 ACH | 221 sq ft |
| Honeywell Air Touch P1 | 450 m³/h | 698 sq ft | 2.8 ACH | 397 sq ft |
| Philips AC3220/60 | 520 m³/h | 135 m² (1,453 sq ft) | 1.6 ACH | 459 sq ft |
Nobody is lying to you here. That gentler assumption is fair in a city with clean outdoor air. It isn't fair in Delhi in November, when the air leaking in around your windows is the problem. Put simply, an air purifier rated for 65 m² is, in a Delhi winter, one for a 20 m² bedroom.
Is CADR more important than HEPA grade?
Yes, once you're at H13 or better. Going from no HEPA to H13 is a huge jump. Going from H13 to H14 is a small one next to the difference between a machine sized right and one sized wrong. Buy the grade to clear H13, then put the rest of your budget into CADR. Our guide to H13 and H14 HEPA filters covers what those grades certify.
Do air purifiers actually work against Delhi smog?
Yes. Trials keep showing indoor PM2.5 falling by half or more. There's a catch about how much of that research carries over to our air, and we'd rather tell you now than let you find out in November.
In a randomised crossover trial published in Scientific Reports, homes running real HEPA units saw indoor PM2.5 fall 52% against sham units. A double blind crossover study in Detroit found portable HEPA filtration cut median indoor PM2.5 by 58 to 65%, and measured a 3.2 mmHg drop in systolic blood pressure over three days (PMC). An eight month trial of H14 units in adults with moderate to severe asthma reported real improvement in Asthma Control Test scores and symptom free days.
Now the catch. Those trials ran in cities where indoor PM2.5 starts around 5 µg/m³. The percentage drop should carry over. The absolute numbers won't. Cutting 65% off a November indoor reading of 180 still leaves you above the WHO 24 hour guideline of 15. A good air purifier cuts your exposure by a lot. It doesn't turn a Delhi winter into Swiss air, and anyone who tells you otherwise is selling something.
Which HEPA air purifier should I buy for my room size?
We've sized these air purifiers by the maths above rather than by the box. Prices move through the year, so these are the brackets each model sits in rather than a figure that'll be wrong by March.
Honeywell Air Touch V3, under ₹10,000
The one we sell most of, and what we suggest when somebody rings and says "I just need something for the bedroom before Diwali." 300 m³/h through an H13 HEPA and carbon stage, which by our formula is a real 265 sq ft. That's more than the 120 sq ft bedroom above, with headroom for a bad night. If you want app control and a 9,000 hour filter, the Honeywell Air Touch V5 sits just above it.
Honeywell Air Touch P1, mid ₹teens
450 m³/h, so a real 397 sq ft. This is the drawing room answer for most flats. It clears the 252 sq ft example with room to spare, which matters because a living room has a front door opening onto a corridor all evening.
Philips AC3220/60, under ₹20,000
520 m³/h, the strongest CADR under ₹20,000 we hold, and a true 459 sq ft. Ignore the 135 m² on the box for the reasons above. Good pick for an open plan living and dining space you can't shut off.
Coway AirMega 250, mid ₹30,000s
The large room air purifier, for people who'd rather not think about this again for years. It carries a 7 year warranty, which is unusual in this category and is the real reason we keep stocking it.
Sharp DW-T30FM-W, low ₹40,000s
For one specific problem: a ground floor or basement that's damp in August and filthy in November. Thirty litres a day of dehumidification plus H14 class filtration on one plug point. If your walls sweat during monsoon, this handles both at once.
Dyson Hot + Cool HP12, upper ₹60,000s
Worth it if you want a heater, a fan and a purifier in one corner instead of three. Buy it for that and for the formaldehyde breakdown, not because it out filters a mid ₹teens Honeywell. On CADR per rupee, it doesn't.
How much does it cost to run an air purifier in Delhi?
Budget roughly ₹2,000 to ₹3,500 a year per machine, filters included. This is the part nobody puts in the guide, and the part people get annoyed about in February.
Filters are the real cost. A Honeywell Air Touch replacement runs about ₹2,500 to ₹3,200 depending on model, and one rated for 9,000 hours lasts roughly two Delhi seasons at 12 hours a day through the bad months. Electricity is the smaller half. Take 45 W for 12 hours over 120 days and you get about 65 units, near ₹500 a season at ₹8 a unit, so check your own slab. An air purifier with a clogged filter is just a noisy box. Our full breakdown of running costs works it through model by model.
Four ways people waste money on this
- Buying by brand instead of by CADR. A ₹35,000 machine sized for the wrong room loses to a ₹10,000 one sized for the right room.
- Running it on silent mode all night. Silent mode is often a fraction of rated CADR. The number on the box is top speed. If the room needs clearing, it has to be audible for the first hour.
- Skipping the pre filter clean. Delhi dust loads a pre filter in weeks. Rinse it monthly through winter and the expensive HEPA lasts its full life instead of half.
- Chasing ionisers and UV add ons. The filtration does the work. Treat the extras as a bonus, never as the reason to buy.
When should I run my air purifier?
From the day AQI crosses 200, overnight in the bedroom at the very least. The Commission for Air Quality Management runs a staged plan for Delhi NCR. It's aimed at construction sites rather than living rooms, but it makes a useful calendar (stage wise GRAP analysis).
| Stage | AQI | Category | What we'd do at home |
|---|---|---|---|
| I | 201 to 300 | Poor | Run it in the bedroom overnight |
| II | 301 to 400 | Very Poor | Bedroom nightly, living room evenings, windows shut |
| III | 401 to 450 | Severe | Continuous in occupied rooms, pre filter checked weekly |
| IV | above 450 | Severe+ | Continuous, top speed for the first hour of each session |
Where can I buy an air purifier online in Delhi NCR?
You can buy an air purifier online from us with delivery across Delhi NCR, or come into the showroom with your room dimensions and we'll do the maths with you. We've been an appliance retailer in this city long enough to have sold most of these machines to people who came back the next winter, which is the only product testing that really counts. If the honest answer for your room is the under ₹10,000 machine rather than the ₹68,000 one, that's what we'll tell you.
More air purifier guides
- Top air purifiers to buy online in India, the national picks beyond Delhi.
- Best air purifiers under ₹9,999, what the budget end actually gets you.
- H13 vs H14 HEPA filters, what the grades certify.
- Air purifiers for winter smog, the seasonal case.
- Benefits for asthma and allergies, the health evidence.
- Sharp FP-J80 vs Honeywell Air Touch U1, a head to head.