Ventilation without letting the smog in
Homes still need fresh air for moisture, cooking fumes and carbon dioxide. How to ventilate smartly on polluted days.
Sealing up keeps outdoor particles out, but homes still need some air exchange. Moisture from cooking and bathing, cooking fumes, and carbon dioxide from people breathing all build up in a closed room.
Ventilate when the outdoor air is cleanest
- Check your nearest station’s hourly reading rather than the daily figure. In Delhi’s winter, pollution is usually worst at night and early morning, when a cold, still layer of air traps smoke near the ground. Concentrations often dip around midday and afternoon, when the ground warms and air mixes higher.
- India’s health ministry advises that on Poor to Severe days, homes should be ventilated only if needed, between 12 noon and 4 pm.
- Air rooms briefly and fully (10–15 minutes with windows wide open) at the cleanest time, then close up and let the purifier clean the room again. This is better than leaving a window slightly open all day.
- Never ventilate during a spike, such as during firecrackers, a nearby fire or heavy traffic hours.
Use the exhausts you have
- Kitchen: use a hood or exhaust fan that vents outdoors whenever you cook, especially frying and tempering (tadka). A recirculating “chimney” with only a grease filter does little for fine particles.
- Bathroom: run the exhaust fan after showers to remove moisture.
When exhaust fans run, they pull replacement air in through gaps elsewhere. That’s fine, and it is one more reason to keep the purifier in a closed room.
Filtered fresh-air systems
If you are renovating or have a larger budget, a filtered fresh-air system brings outdoor air in through a high-grade filter and can keep the home at a slight positive pressure, so polluted air doesn’t leak in through gaps. What to look for:
- a filter rated MERV 13 or better, or a HEPA stage;
- a heat or energy-recovery core (ERV/HRV) if it will also run in summer and winter;
- a sealed installation, with an accessible filter that is easy to replace.
These systems complement room purifiers. They don’t replace them. See ventilation systems in the buying guide.
Signs a room needs more air
Stuffiness, condensation on windows in the morning, lingering cooking smells, or headaches on waking. An optional carbon dioxide (CO₂) monitor using an NDIR sensor shows when a bedroom needs airing. If readings climb well above 1,000 ppm overnight, the room needs airing.