Delhi Air Pollution: How many air purifiers should I have in my home?

When Delhi-NCR’s AQI climbs above 600, a single air purifier barely scratches the surface. Here’s a realistic breakdown of how many you actually need and why.

Delhi Air Pollution: This isn’t a sales pitch for air purifiers. I’m not here to convince you that buying more machines will magically fix Delhi’s air. The truth is, the best health advice anyone can give right now is to leave the city altogether and move somewhere that doesn’t need an AQI app to decide when to breathe. But for most of us, packing up our lives and jobs isn’t an option. That leaves us with the next best thing: air purifiers. They’re far from perfect, but compared to the cost and complexity of HVAC systems with full-scale filtration, they’re the most practical defence you can afford.

Delhi Air Pollution: For a 1500 sq ft, 3BHK apartment in Delhi NCR, three to four high-CADR air purifiers are needed for effective protection when AQI exceeds 600. (Arvind Yadav/HT)

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It’s worth noting that even the best standard purifiers can only capture particulate matter like PM2.5 and PM10, they do little against gaseous pollutants such as nitrogen oxides or volatile organic compounds. Still, they can significantly reduce the immediate health risks from prolonged exposure.

When Delhi NCR’s AQI pushes past 600, one air purifier simply can’t handle the load. To make any real difference indoors, you need multiple units strategically placed and matched to each room’s size. Here’s a grounded, numbers-backed breakdown of how many you actually need for a typical 3BHK apartment of around 1500 sq ft, and why.The solution is not about buying the biggest purifier available. It’s about correct distribution, coverage, and airflow. The rule of thumb is straightforward: one purifier per enclosed space where people spend significant time. This means you’ll need one unit in the master bedroom, another in the secondary bedroom, and at least one large or two medium units in the living and dining area. That totals three to four purifiers for meaningful air cleaning. Relying on a single unit in such conditions will leave most of your home unprotected, as air circulation rarely reaches every corner effectively.

Here’s a practical breakdown:

• Master Bedroom: One purifier with a CADR (Clean Air Delivery Rate) of 350–450 m³/h. It should be kept away from walls and corners, ideally near the bed at breathing height.
• Second Bedroom or Study: One purifier with a similar CADR rating, positioned to allow air to circulate across the entire room.
• Living and Dining Area: Since this is often the largest and most open space, you’ll need a high-capacity unit with a CADR of 600 m³/h or higher, or two smaller purifiers working together. Place them on opposite ends of the room for better coverage.
• Additional protection: If your kitchen opens into the living area or your layout has connecting hallways, consider an additional compact purifier near the transition space to contain cross-contamination.

Start by choosing the right size for each room. Every purifier has a CADR rating, which decides how efficiently it can clean the air. Match that CADR to your room’s size using a simple rule, otherwise, your purifier will end up running all day without making much difference.

What CADR actually means:CADR stands for Clean Air Delivery Rate. It measures how quickly a purifier removes pollutants from the air, expressed in cubic feet per minute (CFM). The higher the CADR, the faster the purifier can clean a given space. Most purifiers list three CADR numbers—one each for smoke, dust, and pollen, because they trap particles of different sizes at different speeds. In most cases, the smoke CADR is the most relevant because smoke particles are similar in size to PM2.5, the most harmful pollutant in Delhi’s air.

In simple terms:

Higher CADR = faster and better cleaningLower CADR = slower cleaning and weaker protection

If your purifier’s CADR is too low for your room, the air simply won’t cycle through the filter often enough, leaving you with little improvement in air quality.

How to size your purifier (the AHAM rule)The Association of Home Appliance Manufacturers (AHAM) offers an easy way to find the right purifier size for your room:

Room area (sq ft) = CADR × 1.55Or, CADR = Room area ÷ 1.55For example:

A 150 sq ft bedroom needs a purifier with at least CADR 100 (150 ÷ 1.55 ≈ 97). Or, a 300 sq ft living room should have a CADR of around 200 or higher.This setup ensures the purifier cleans the air four to five times every hour, which is what’s required to keep PM2.5 levels in check in a city like Delhi.

How to get the most out of your air purifier

1. Keep it running whenever the room is in use. Especially at night in bedrooms, turning it on and off in short bursts doesn’t work against steady pollution exposure.
2. Place it correctly. Keep the unit away from walls and corners so air can circulate freely. The best spot is near where you sit or sleep.
3. Control indoor pollution sources. Avoid incense, candles, frying, or smoking indoors. Always use your kitchen exhaust while cooking and keep doors closed to stop smoke from spreading. If cooking fumes are a daily issue, consider adding a small purifier in the kitchen too.
4. Seal and ventilate smartly. Keep windows closed during high-smog hours and open them briefly around noon when outdoor AQI dips. If your home has a mechanical ventilation system, use the recirculation mode with proper filters.

Filter performance also matters more than marketing claims. In Delhi’s severe smog, filters clog faster– expect replacements every three to four months instead of the usual six to twelve. Keep doors and windows closed when purifiers are running, and if you must ventilate, do it around noon when outdoor AQI briefly dips. Running purifiers on turbo mode for 20–30 minutes before bedtime can quickly refresh indoor air, after which medium mode is sufficient for the night.

A small but useful addition is an indoor air quality monitor. Devices from brands like Qingping or Kaiterra give you real-time data, helping you see which rooms improve faster and when filters need cleaning.

Ultimately, for a 1500 sq ft, 3BHK home in Delhi NCR, three to four air purifiers are the bare minimum for reliable indoor protection when the AQI crosses 600. Anything less, and you’re only diluting polluted air, not cleaning it.