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

Every winter, as the air quality index in north Indian cities slips into the "poor" and "very poor" bands, searches for air purifiers shoot up. After Diwali 2026, CPCB data showed Noida's average AQI at about 340 and Ghaziabad's at around 357 to 366 on 9 November 2026, both in the "very poor" category, while Lucknow's daily average rose from 223 on 7 November to 315 on 8 November 2026. If you are thinking of buying a purifier, these are the specifications that actually matter, and the marketing claims you can ignore.

1. CADR: the number that matters most

CADR (Clean Air Delivery Rate) tells you how much filtered air a purifier delivers, usually in cubic metres per hour (m³/h) or cubic feet per minute (CFM). A higher CADR cleans a room faster. A widely used rule of thumb from the US appliance standards body AHAM is to choose a purifier whose smoke CADR in CFM is at least two-thirds of the room's floor area in square feet, for a room with a standard ceiling height of about 8 feet. For example, a 150 sq ft bedroom needs a smoke CADR of at least 100 CFM (roughly 170 m³/h). In heavily polluted cities, buying more than the minimum helps.

2. A real HEPA filter

PM2.5, the fine particulate matter behind most winter smog, is best captured by a HEPA filter. Look for "True HEPA" or a grade such as H13 under the European EN 1822 standard, rather than vague terms like "HEPA-type" or "HEPA-like". An activated carbon layer helps with smells and some gases, but it does little for PM2.5 on its own.

3. Avoid ozone

Some purifiers use ionisers or ozone generators. Ozone is itself a lung irritant, so avoid machines that deliberately produce it, and check the product's specifications for ozone emission before buying.

4. Noise and running cost

A purifier only works if you leave it on. Check the noise level (in decibels) at the speed you will actually use at night, and the power consumption. Many models have an "auto" mode with a built-in PM2.5 sensor that raises the fan speed when the air gets worse.

5. Filter replacement

Replacement filters are the hidden cost. Before buying, check the price and availability of genuine filters in your city and how often the manufacturer recommends changing them. In very polluted conditions filters clog faster than the brochure suggests.

6. Use it correctly

• Keep doors and windows closed while it runs; a purifier cannot clean the whole outdoors.
• Place it where air can flow freely around it, not pushed into a corner.
• Run it in the room where you spend the most time, usually the bedroom at night.
• Check your city's AQI daily on CPCB's Sameer app and plan outdoor activity around it.

The bottom line

Pick the right CADR for your room, a genuine HEPA filter, no ozone, a noise level you can sleep with and filters you can actually buy. A purifier helps indoors, but on very poor and severe days, limiting time outdoors and wearing a well-fitted N95 mask outside still matter.

VoxyTalksy does not recommend any specific brand and has not been paid for this guide.