Why most air purifiers fail in Delhi's winter

Every November, Delhi's air quality index crosses 200. Sometimes 400. Sometimes the monitors stop counting. And every November, lakhs of families switch on their air purifiers and trust the green light.

The problem with imported filters

70% of air purifiers sold in India are designed for cities like Tokyo, Seoul, or Munich — where average PM2.5 levels hover around 10–15 µg/m³. Delhi's winter average is 178 µg/m³.

That's not a minor difference. That's a 12× difference in particulate load.

A HEPA filter designed for Tokyo air will last 12–18 months in Tokyo. In Delhi, during winter, the same filter clogs in 15–30 days.

The green light problem

Most air purifiers use a simple timer — not actual filter monitoring — to drive their indicator light. The device counts runtime hours and assumes the filter is fine until a preset threshold.

In Delhi's air, the filter is dead long before the timer runs out.

The green light stays on. The air passing through is unfiltered. And you don't know.

What we're building differently

At Novayu, we started with Delhi's air, not a lab in Osaka. Our four-stage filtration system uses a 15-year washable pre-filter that captures 93–96% of large particles before air reaches the HEPA. The result: a HEPA filter that lasts 20–28 months, even in Delhi's worst winter.

And our device doesn't use a timer. It uses actual sensor data to predict when the filter will fail — 18 days before it does.

Because a green light should mean something.