Air Purifier Buying Guide India — HEPA, CADR, and Room Size
Air Purifier Buying Guide India — how to size a purifier to your room, why CADR and true HEPA matter, and the running costs to plan for.
With Indian city air routinely crossing hazardous AQI levels, an air purifier has moved from luxury to necessity — but the marketing is full of vague "room coverage" claims and gimmick filters. This guide explains the two numbers that actually matter (CADR and filter grade), how to size a purifier correctly, and the running costs to budget for.
We have researched and evaluated air purifiers to distil the decision factors below. Size to your room using CADR first, then confirm a genuine HEPA-plus-carbon filter.
Looking for picks first? See Best Air Purifiers in India (2026).
Key Decision Factors
1. CADR — The Only Coverage Number That Matters
CADR (Clean Air Delivery Rate) states how much clean air a purifier delivers per hour; higher means faster cleaning. Size it to your room: multiply the room area (sq ft) by about 1.5 for the minimum CADR in m³/h, and aim for at least 3-4 air changes per hour. Compare real CADR figures across models in Best Air Purifiers in India (2026).
| Room Size | Minimum CADR | Typical Use |
|---|---|---|
| Under 200 sq ft | 200 m³/h | Small bedroom |
| 200-400 sq ft | 300-400 m³/h | Living room |
| 400-600 sq ft | 500-600 m³/h | Large hall |
| 600+ sq ft | 800+ m³/h | Commercial spaces |
2. HEPA Filter — True HEPA, Not "HEPA-Like"
True HEPA (H13/H14) captures 99.97% of particles down to 0.3 microns — PM2.5, dust, pollen, and bacteria. "HEPA-like" or "HEPA-type" filters capture only 85-90%, a meaningful gap on a bad-AQI day. Verify the exact grade before buying; H13 is the sensible minimum.
3. Activated Carbon — For Gases, VOCs, and Odours
HEPA traps particles; activated carbon handles gases, formaldehyde, VOCs, and cooking or traffic odours. Carbon weight matters — thin mesh coatings do little. Look for a substantial carbon layer (500g+), especially if you live near traffic or industry.
4. Noise Level — It Runs While You Sleep
Because a purifier runs continuously, noise is a real comfort factor. Under 25 dB on low is whisper-quiet, 30-40 dB is noticeable but tolerable, and 50 dB+ disrupts sleep. Check the rating at the speed you will actually need for effective cleaning, not just the marketed sleep-mode figure.
5. Running Costs — Filters Are the Real Expense
The sticker price is only the start. HEPA filters last 6-12 months and carbon 3-6 months, at ₹1,500-4,000 per set, putting annual running cost (filters plus electricity) around ₹3,000-8,000. Choose a brand whose replacement filters are easy to buy in India.
6. Related Air Comfort — Humidity Matters Too
A purifier cleans particles but does nothing for humidity, which swings hard across Indian seasons. In the sticky monsoon, a dehumidifier prevents damp and mould; in dry winter or AC-heavy rooms, a humidifier eases dry skin and irritated airways. Pairing the right one with your purifier makes indoor air genuinely comfortable.
Common Mistakes to Avoid
Trusting "room coverage" claims over CADR. Brands overstate coverage; a purifier "rated for 500 sq ft" may take an hour for one pass. Calculate air changes per hour from CADR and aim for at least 3.
Running it only on bad-AQI days. Indoor air carries dust, cooking fumes, and furniture VOCs even when outdoor AQI is fine. Run the purifier continuously on low for consistently clean air.
Opening windows while it runs. A purifier cleans indoor air; open windows let outdoor pollution back in and make it work harder for nothing. Keep the room reasonably sealed.
Falling for ioniser and UV gimmicks. HEPA plus activated carbon is the proven combination. Ionisers can emit trace ozone, and UV lamps rarely get enough exposure time to matter. Skip the add-ons and buy filtration.
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Dyson leads on premium build but costs the most. Sharp and Coway offer excellent filtration at mid-range prices, and Mi and Coway are popular in the ₹8,000-15,000 segment with strong CADR. Match the CADR to your room rather than choosing on brand alone.
Most home purifiers draw 30-70 watts — similar to a ceiling fan — so running 24/7 costs roughly ₹150-400 a month. That is far less than an AC, and the ongoing filter cost matters more than the electricity.
HEPA plus activated carbon is the proven, effective combination. Ionisers can produce trace ozone that irritates lungs, and UV-C lamps usually lack enough exposure time to reliably kill pathogens. Prioritise filtration and skip the gimmicks.
Multiply your room area in square feet by about 1.5 for the minimum CADR in m³/h, and aim for 3-4 air changes per hour. A typical 150-200 sq ft bedroom wants a CADR of around 200-300 m³/h for effective cleaning.