BreatheBetterDelhi NCRTools

Protect your home

Make one clean room first

The single most effective thing a household can do is turn one room into a well-filtered refuge, starting where the most sensitive person sleeps.

Cleaning the air in a whole home is expensive. Cleaning the air in one closed room is achievable on most budgets, and it covers the 7–9 hours a day everyone spends asleep. Public-health agencies recommend this “clean room” approach for smoke and pollution episodes.

Which room?

  1. The bedroom of the most sensitive person: an older adult, a baby or young child, someone pregnant, or anyone with a heart or lung condition.
  2. If they share a room, or two people are equally vulnerable, size each closed bedroom separately.
  3. Next, the room where the household spends the day (often the living room), if it can be closed off.

A small room with a door that shuts is easier to keep clean than a large open-plan space.

Five steps

  1. Close it up. Keep windows and the door shut during bad spells. Close gaps that let outdoor air in: see sealing gaps.
  2. Run a correctly sized HEPA purifier, continuously. Use the calculator below. The US EPA advises running it on the highest fan setting you can, continuously. Run it all day and night during bad spells, not just when the AQI looks worst, because indoor air takes time to clean and dirties again quickly.
  3. Make no smoke inside. No incense, dhoop, mosquito coils, candles or smoking in or near the room. See indoor sources.
  4. Keep it ventilated safely. People breathing in a sealed room raise carbon dioxide and humidity. Air it briefly when outdoor air is cleaner, or use filtered ventilation. See ventilation.
  5. Check it works. An indoor PM2.5 monitor shows whether the room actually gets clean, including at the quieter fan speed used overnight. See measuring indoor air.
Interactive

How powerful a purifier does this room need?

Units
A 10 × 12 ft bedroom is 120 ft² (about 11 m²).
Target clean-air changes per hour
Higher is better on very bad days, for leaky rooms, or where a sensitive person sleeps.
Look for a published particle (smoke / PM2.5) CADR of at least
204 m³/h
≈ 121 CFM, at the fan speed you will actually use.
  • Ignore the “suitable for up to X ft²” claim on boxes. Brands calculate it in different ways, sometimes assuming only 1–2 air changes per hour. Compare CADR instead.
  • Quiet or sleep modes deliver much less than the maximum CADR. If the night-time speed is too weak, size up or add a second unit.
  • Two purifiers in one open space add together. Size closed rooms separately.
How this is calculated

CADR (m³/h) = area (ft²) × height (ft) × 0.0283 × air changes per hour, rounded up. The result is a design target. Actual indoor levels also depend on leaks, indoor sources and how well the air mixes.

Why sealing and the purifier work together

Outdoor air leaks in through gaps all the time. The purifier removes particles from the room’s air, and sealing slows how fast new particles arrive. Doing both is better than either alone. Try it:

Interactive

Clean-room simulator

See how sealing gaps, closing the door and running a purifier change the air inside one room. This is an educational model, not a forecast.

How airtight is the room?
Indoor PM2.5 falls from 167 to about 21 µg/m³ over 60 min after the purifier starts; outdoor is 250.068135203270purifier on15 min30 min45 min60 minOutdoor 250WHO 24-h guideline 15
Indoor PM2.5 settles at about
21 µg/m³
92% below outdoor, within about 14 minutes. Purifier provides 8.4 clean-air changes per hour.

What each step adds (door closed)

  • Leaky room, no purifier227 µg/m³
  • Sealed room, no purifier105 µg/m³
  • Leaky room + 300 m³/h purifier47 µg/m³
  • Sealed room + 300 m³/h purifier6 µg/m³

Bars show indoor PM2.5 as a share of the outdoor level (250 µg/m³).

Assumptions

Single well-mixed room with a 9 ft ceiling. Particles settle on surfaces at 0.2/h. Air leaks in at:

  • Leaky (gaps under doors, old window frames): 2 air changes/h, 100% of outdoor particles get through
  • Average (windows shut): 1 air changes/h, 80% of outdoor particles get through
  • Sealed (weatherstripped, door sweep): 0.3 air changes/h, 70% of outdoor particles get through
  • Windows open: 8 air changes/h, 100% of outdoor particles get through

These values are illustrative: there are no published air-leakage measurements for Delhi homes. The purifier is assumed to deliver its rated CADR, and it delivers less at lower fan speeds. Use an indoor PM2.5 monitor to check your own room.

What about the air conditioner?

A split AC mostly recirculates room air. Its basic mesh filter catches dust and hair but not fine particles, so it does not replace a purifier. It doesn’t hurt either. Running the AC with windows shut is fine, and some newer units have better filters. A window or “desert” (evaporative) cooler pulls large amounts of outdoor air into the room and works against a clean room on polluted days.

If money is tight