Indoor air & sleep
Your bedroom is probably the worst-ventilated room you use.
You spend about a third of your life in it with the door shut and the window closed. By four in the morning it is holding more carbon dioxide than the office everybody worries about, and you have slept through every minute of the climb.
How much CO₂ is in a closed bedroom overnight?
A closed single-occupancy bedroom of about 12 m² typically rises from around 500 ppm at lights-out to between 2,000 and 2,500 ppm by morning. Two people reach the same level in roughly half the time. Opening a window on the latch, or simply leaving the door open, usually holds the room under 1,000 ppm all night.
One night, one sleeper, door shut
Nothing about it feels different at any point
Modelled with the same accumulation maths the room calculator uses: 12 m², 2.4 m ceiling, one sleeping adult, 0.2 air changes per hour. Your room will differ, which is rather the point of measuring yours instead of reading ours.
| Time | CO₂ | What that is |
|---|---|---|
| 23:00 | 500 ppm | Lights out, with the room still close to outdoor air. |
| 00:30 | 1,100 ppm | Past the point where ventilation guidance would call the room under-ventilated. |
| 02:00 | 1,700 ppm | Higher than the office that the rest of this site worries about. |
| 04:00 | 2,300 ppm | Around the concentration the bedroom studies associate with measurably worse sleep. |
| 07:00 | 2,500 ppm | Roughly where it settles out. This is the air you wake up in, and it feels like nothing in particular. |
Free, no sign-up, and quite likely to tell you your room is fine.
The instrument
OptiBreath logs the whole night and tells you in the morning what the room actually did.
It is not shipping yet. Founding units are scheduled for Q1 2027. The waitlist takes an email address and nothing else, and whether you buy one is a decision for the day we write to you.
What measuring it is for
The monitor will not improve your sleep. A window might.
The case for an instrument here is unglamorous. It tells you whether you have a problem at all, what the smallest thing is that would fix it, and whether that fix is still working in March.
Find out whether your bedroom is a problem at all
Plenty are not. A draughty older building, a door left ajar, a room with trickle vents: any of these may sit under 900 ppm all night quite happily. If yours does, that is a thing you now know and can stop wondering about.
Find the smallest change that fixes it
A window on the latch usually does it. An open door frequently does it on its own. The reason to measure is to find the least disruptive fix rather than the most thorough one, because nobody is going to sleep cold all winter to improve a reading.
Check it held
Ventilation shifts with the weather, with the season, and with whether the door drifted shut at some point after midnight. One good night does not mean a solved room, which is more or less the argument for owning an instrument rather than borrowing one for a week.
The evidence
Better supported than the argument this company was founded on
The bedroom-ventilation literature is a good deal smaller than the office-cognition literature. It has also been rather less contested, which is an awkward thing for us to have to report.
Indoor Air, 26(5) · 2016
The effects of bedroom air quality on sleep and next-day performance
Strøm-Tejsen, P., Zukowska, D., Wargocki, P., & Wyon, D. P.
In two field experiments in real bedrooms, reducing overnight CO₂ from roughly 2,400 ppm to roughly 800 ppm — by opening a window or running a fan — improved measured sleep quality and self-reported freshness on waking, and improved performance on a next-morning test of logical thinking.
Indoor Air, 28(3) · 2018
Window/door opening-mediated bedroom ventilation and its impact on sleep quality
Mishra, A. K., van Ruitenbeek, A. M., Loomans, M. G. L. C., & Kort, H. S. M.
Bedrooms with a window or door left open showed substantially lower overnight CO₂ and were associated with better sleep-quality scores than the same rooms sealed.
What this does not show
- These are field studies with small samples, and the mechanism is not settled. Bedroom CO₂ rises alongside humidity, temperature and bioeffluents, and the experiments that improved ventilation moved all of them at once.
- CO₂ has not been established as the direct cause of worse sleep. What it gives you is a measurable, controllable marker for the ventilation rate that plausibly is.
- No monitor has ever improved anyone's sleep. Opening a window might. The instrument's job is telling you whether it worked, and on which nights it quietly stopped working.
The counter-evidence for the cognition claim is set out on the science page, and it is here for the same reason: a claim you have no way of checking is not really a claim.
Common questions
Bedroom CO₂, answered.
- How much CO₂ is in a bedroom overnight?
- A closed single-occupancy bedroom of about 12 m² with little ventilation typically rises from around 500 ppm at lights-out to between 2,000 and 2,500 ppm by morning. Two occupants reach the same level roughly twice as fast. An open window or an open door usually holds the room under 1,000 ppm.
- Does CO₂ in a bedroom affect sleep?
- Field studies that improved bedroom ventilation — lowering overnight CO₂ from roughly 2,400 ppm to roughly 800 ppm — measured better sleep quality and better next-morning logical thinking. Those studies changed ventilation as a whole rather than CO₂ alone, so CO₂ is best understood as the measurable marker for ventilation rather than the established direct cause.
- What CO₂ level should a bedroom be?
- Under 1,000 ppm is a reasonable target and is what most ventilation guidance implies for an occupied room. Below 800 ppm is comfortably ventilated. Sustained readings above 2,000 ppm indicate the room is effectively sealed against outdoor air.
- How do I lower CO₂ in my bedroom?
- Open a window on the latch, or leave the bedroom door open to the rest of the home. Both usually move a sealed room from around 2,400 ppm to under 1,000 ppm. Plants do not measurably help at the rate a sleeping adult produces CO₂, and an air purifier does not remove CO₂ at all — it filters particulates.