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Ventilation and indoor air (CO₂)
That stuffy, heavy feeling in a closed room is largely about ventilation. As people breathe, carbon dioxide (CO₂) builds up, and it is a good proxy for how fresh — or stale — the air is.
Why fresh air matters
Outdoor air is around 400 ppm CO₂. In a shut bedroom or a full meeting room it can climb past 1,000–1,500 ppm, and studies link that stale range to worse concentration, headaches and drowsiness. Good ventilation also clears cooking moisture, everyday indoor pollutants and, importantly, the airborne particles that spread respiratory infections.
Simple wins
You do not need a mechanical system to fix most rooms. Airing out — opening windows wide for a few minutes several times a day (cross-ventilation is fastest) — resets the air quickly, even in winter. Sleep with a window ajar or the door open if you can. A cheap CO₂ monitor turns "it feels stuffy" into a number you can act on.
| Indoor CO₂ | Air quality |
|---|---|
| Below 800 ppm | Fresh, well ventilated |
| 800–1000 ppm | Acceptable |
| 1000–1400 ppm | Stuffy — concentration dips |
| Above 1400 ppm | Poorly ventilated — air it out |
More on a healthier home
Bedroom temperature for sleep
A cool room helps you fall asleep and stay asleep. The usual sweet spot is around 16–19 °C.
Tap water and water hardness
In most of Europe tap water is safe and well tested. "Hard" or "soft" is about minerals, not safety.
Indoor humidity and mould
Aim for 30–50% relative humidity. Above 60% invites mould and dust mites; below 30% dries you out.
Radon in the home
An invisible ground gas that builds up indoors in some areas. The only way to know your level is to test.
Source: General building-health guidance (WHO indoor-air and radon references and national health and water authorities). · checked 2026-09-04
Frequently asked questions
Does opening a window in winter waste heat?
Briefly airing a room — windows wide for a few minutes — swaps the stale air without cooling the walls and furniture much, so it costs far less heat than leaving a window on the tilt all day. It is the efficient way to freshen a room.
Is high CO₂ indoors dangerous?
The levels found in a stuffy room are not toxic, but they reliably signal poor ventilation and go with reduced concentration and headaches. Very high CO₂ would be a concern, which is another reason to keep air moving.
See what actually improves your sleep
TempoLife tracks sleep, hydration and more, so a change at home becomes a visible trend.