Sleep Coaching

Stale Bedroom Air: CO₂ and Your Sleep

How carbon dioxide builds up in a closed bedroom overnight, what the studies show about sleep and next-day focus, and cheap fixes.

Every breath you exhale adds carbon dioxide to the room. With the bedroom door and window shut, and two people (or a dog) breathing all night, CO₂ climbs for hours because little fresh air comes in. Outdoor air is roughly 420 ppm today (NOAA). In closed bedrooms, researchers have measured nightly averages well above 2,000 ppm.

CO₂ at these levels isn’t dangerous by itself. Mostly it signals that the room isn’t getting enough fresh air, and other stale-air pollutants build up along with it.

What the studies show

• Danish dorm study: opening a window, or running a quiet intake fan, cut average bedroom CO₂ from about 2,400–2,600 ppm to 660–835 ppm. With the lower CO₂, sleep measured by wrist trackers improved, and the next day people reported less sleepiness and better concentration and scored better on a logical-thinking test. These were small samples of 14 and 16 students (Strøm-Tejsen et al., 2016, Indoor Air).
• Dutch window/door study: with the bedroom window or door open, average CO₂ was about 717 ppm, compared with 1,150 ppm closed. People rated their sleep as deeper with it open. The study had 17 volunteers (Mishra et al., 2018, Indoor Air).
• Sydney home study (48 people): each 100 ppm rise in overnight CO₂ was linked to 4.3% less deep sleep as estimated by wrist sensors. Warmer bedrooms were linked to lower sleep efficiency and less REM (Xiong, Lan et al., 2020). This is an association, not proof of cause.
• Controlled bedroom study (36 people): compared with ventilation giving about 750 ppm, nights at about 1,000 and 1,300 ppm had slightly lower sleep efficiency (1.3% and 1.8%) and a few more minutes awake (Kang et al., 2023, Building and Environment).
• 40 Danish homes in winter: a field study of opening windows or doors is worth a read if you live somewhere cold (Fan et al., 2022). A 2020 review sums up the evidence and current standards (Sekhar et al., 2020).

The honest summary: the studies are small and the effects are modest, but they point the same way. A fresher bedroom seems to help a bit, and fixing it is cheap.

Our editor’s bedroom readings

Our editor uses the GoveeLife H5140 at home. Here are her hourly CO₂ highs on two nights in a row, one with the bedroom door shut and one with it cracked open. We redrew them from her app’s charts; values are approximate.

With the door shut, every hourly high from 2 AM to 8 AM was above the app’s 973 ppm line, roughly 1,070 to 1,190 ppm (the chart’s top is 1,255 ppm). The next night, with the door cracked, every hourly high from midnight to 7 AM stayed between the 691 and 973 ppm lines, roughly 720 to 880 ppm. Simply cracking the door kept CO₂ under about 970 ppm all night. This is two nights in a row in one bedroom, using hourly highs from her Govee monitor. It isn’t a controlled study.

Practical fixes

• Measure first. A CO₂ monitor like the GoveeLife H5140 shows whether your room actually gets stuffy. Set its night schedule so the screen stays dark.
• Crack the bedroom door or a window. In the studies above, this alone made a big difference to CO₂.
• Run the HVAC fan, if your system brings in outdoor air. An ERV or HRV brings in fresh air while recovering much of the heat or cool, which is how you stay ventilated without blowing up the energy bill.
• Don’t count on houseplants. A review found you’d need impractically many plants to match ordinary ventilation (Cummings & Waring, 2019).

If you sleep cold, like we do

A cold, sealed room can still be a stuffy one. Cooling the bed itself (see the bed temperature control price ladder) lets you keep the room comfortable, so cracking the door doesn’t mean overworking the AC. Watch the monitor and find the smallest opening that keeps CO₂ in check.

Educational only, not medical advice. Talk to your doctor about ongoing sleep problems.

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