Air purifiers 101: CADR, filters, and myths you should know before investing

Indoor air can hide dust, smoke, and pollutants that affect health. Here’s what you need to check before buying an air purifier for your home and office.

Indoor air quality affects health, comfort, and daily life. Dust, pollen, smoke, and other particles can trigger allergies, respiratory issues, and fatigue. Increasing pollution in many cities, mostly in metro cities like Delhi and Mumbai, has made air purifiers a common household item rather than a luxury. Choosing the right device, however, requires understanding how it works, the type of filters it uses, and maintenance requirements.

Things you should know about before buying an air purifier for your home.

By MD Ijaj Khan

Ijaj Khan is a technology journalist and Senior Content Producer at Hindustan Times, with over three years of experience covering the consumer technology industry. His work spans smartphones, laptops, wearables, gaming, appliances and AI - from hands-on reviews, comparison and buying guides to breaking news and in-depth features that help readers cut through the noise and make informed decisions. Before joining HT Tech, he worked with Jagran New Media, where he sharpened his instincts for fast-paced digital reporting. He holds a Post Graduate Diploma in English Journalism and Mass Communication from the Indian Institute of Mass Communication (IIMC), Delhi. Whether he's testing the latest flagship smartphone, tracking a major AI announcement, or putting a gaming laptop through its paces, Ijaj approaches every story with the same goal - making technology feel relevant and easy to understand for everyday users, not just enthusiasts. When he's not in front of a screen for work, he's usually travelling to a new city, hunting for great food, or keeping tabs on what's next in tech before everyone else catches on.

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How Air Purifiers Work

Air purifiers clean indoor air through continuous filtration. They usually include a fan that draws air in, filters that trap particles, and sometimes sensors that adjust airflow based on air quality. Pollutants such as PM2.5, PM10, dust, pollen, pet dander, and some harmful gases get captured by filters, and the purified air is released back into the room. Repeating this cycle gradually lowers indoor pollution levels.

Common Filter Types

1. HEPA Filters: True HEPA filters capture fine particles like PM2.5, which can affect the lungs and heart. HEPA-type or HEPA-like filters are cheaper but less efficient.
2. Activated Carbon Filters: These remove gases, odours, fumes, and chemicals. They do not reduce particulate matter.
3. Pre-Filters: Capture larger debris such as hair and dust, extending the life of the main filter.
4. Ionisers and Plasma Systems: Release charged ions that make particles settle. They may produce ozone, which can irritate the lungs.
5. UV-C Technology: Kills bacteria or viruses but does not replace particulate filtration.
6. Hybrid Purifiers: Combine multiple filters, sometimes including UV-C or ionisers, with effectiveness depending on design rather than quantity of filters.

Factors to Consider Before Buying

• CADR (Clean Air Delivery Rate): Indicates how much clean air a purifier can deliver per hour. Ensure CADR matches the room size.
• Filter Replacement: Check availability, cost, lifespan, and local service options.
• Energy Use and Noise: Devices run for long hours, so energy efficiency and quiet operation are important.
• Smart Features: Wi-Fi, mobile control, and AQI displays can help track air quality, but are not essential.
• Design: Airflow paths should allow effective circulation; multiple intake points and top outlets improve performance.

Common Myths

Air purifiers clean only the room they are in, not the entire house. HEPA filters do not remove odours or gases; activated carbon handles that. They are useful year-round, not just in winter, and a larger size does not guarantee better cleaning. Air purifiers reduce particles but cannot fully protect against viruses or infections.