Air Purifier Buying Guide for Indian Homes: CADR, HEPA and Room Size

With air quality in many Indian cities regularly reaching unhealthy levels, especially in winter, an air purifier has become an essential appliance for many homes. But numbers like CADR, H13 and “coverage area” can be confusing. Here is what they mean and how to choose.

1. CADR: the most important number

CADR (Clean Air Delivery Rate) tells you how much filtered air the purifier delivers, usually in cubic metres per hour (m³/h). A higher CADR cleans a room faster. As a rough rule, choose a purifier whose CADR is at least 4 to 5 times your room’s volume per hour for polluted conditions.

Example: a 150 sq ft bedroom with a 10 ft ceiling is about 42 cubic metres, so a CADR of roughly 170 to 210 m³/h or more is a good target.

2. Room size and coverage claims

Manufacturers’ coverage figures are often optimistic. It is safer to buy a purifier rated for a larger room than you have, and run it on a lower, quieter speed.

3. Filters

• True HEPA (H13 or higher): captures very fine particles, including PM2.5. This is the filter that matters most.
• Activated carbon: helps reduce odours, smoke and some gases.
• Pre-filter: traps hair and large dust, extending the HEPA filter’s life. A washable pre-filter saves money.

Be cautious of vague terms like “HEPA-type” or “HEPA-like”, which may not meet true HEPA standards.

4. Running costs

Replacement filters typically need changing every 6 to 12 months, depending on pollution and usage. Check the price and availability of replacement filters before you buy, because over a few years they can cost more than the purifier itself.

5. Useful features

• PM2.5 sensor and AQI display: shows your indoor air quality in real time.
• Auto mode: adjusts fan speed based on air quality.
• Sleep mode: low noise and dimmed lights for bedrooms.
• Filter-change indicator: tells you when to replace filters.
• App control: nice to have, but not essential.

6. Things to avoid

Avoid purifiers that rely mainly on ionisers or that produce ozone, as ozone can irritate the lungs.

Quick checklist before you buy

1. Measure your room and calculate the CADR you need.
2. Insist on a true HEPA (H13 or higher) filter.
3. Check replacement filter cost and availability.
4. Look for a PM2.5 sensor and auto mode.
5. Check noise levels if it is for a bedroom.

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