Bedroom CO₂ and sleep: what the research shows, and what it doesn't

Most of what we know about indoor air comes from offices and classrooms, where people are awake. Bedrooms are different: the door is often shut, the same air sits around you for eight hours, and nobody notices it getting stale because they're asleep. Here's what researchers have found when they looked at bedrooms specifically.

How bedroom studies work

Almost none of these studies pump CO₂ into a room. They change how much outdoor air reaches the bedroom (a window, a fan, a mechanical ventilation setting) and use the CO₂ level to describe how well ventilated the room was. Sleep is measured with wrist or under-mattress trackers, sometimes with a full lab sleep test (polysomnography), plus questionnaires and, in some, a next-morning thinking test.

That matters for reading the results. When a study says "1,000 ppm," it usually means "the ventilation rate that left the room at an average of 1,000 ppm," not "1,000 ppm of CO₂ added to otherwise fresh air."

The 2025 ASHRAE review (1837-RP)

What it is. A review led by Mizuho Akimoto (Waseda University) with colleagues from the Technical University of Denmark and Shanghai Jiao Tong University, funded by ASHRAE as research project 1837-RP and published in Science and Technology for the Built Environment.

What it covered. 17 studies containing 22 experimental datasets on bedroom ventilation and sleep.

What it found. The lowest CO₂ level at which sleep was disturbed (the best-ventilated condition that still affected sleep) was about 1,000 ppm. The highest level with no observed effect was 850 ppm, which the authors didn't treat as a firm no-effect level, given sensor accuracy and the need for a safety margin. They recommend 800 ppm as the bedroom ceiling, which takes about 8 L/s (17 cfm) of outdoor air per sleeper, at least twice what many current residential standards provide.

In their words. The lead author summed it up as: current minimum ventilation rates for homes "may provide inadequate ventilation for bedrooms."

This review is the main basis for HouseExhale's 800 ppm goal.

Kang et al. (2024): three ventilation levels, 36 sleepers

Who and where. Researchers at Shanghai Jiao Tong University and the Technical University of Denmark, published in Building and Environment. 36 healthy young adults slept in simulated bedrooms.

What changed. Each person slept two nights at each of three ventilation rates, in a balanced order, giving average CO₂ of about 750, 1,000 and 1,300 ppm.

What they found. Compared with 750 ppm:

People who slept worse also did worse on next-day thinking tests. The authors' conclusion is in their title: ventilation that leaves a bedroom at an average of 1,000 ppm has negative effects on sleep, and should be avoided.

Wang et al. (2023): one, two or three sleepers' worth of CO₂

Who and where. Wang and colleagues, published in Buildings. 10 young adults, 30 nights of full lab sleep tests over more than a month.

What changed. CO₂ was set to mimic one, two or three people sleeping in a sealed room, averaging about 680, 920 and 1,350 ppm. This is one of the few studies that varied CO₂ directly.

What they found. The share of deep sleep fell as CO₂ rose, from about 20% to 17% to 14%. Body movements rose by about half at the highest level, and people rated the air worse and reported more throat and nose discomfort.

Keep in mind. Ten people is a small group, and the room was kept warm (about 26–27 °C, 79–81 °F).

Fan et al. (2023): real homes in Belgium

Who and where. An international team led by Xiaojun Fan, published in Science of the Total Environment. 35 adults aged 27 to 64 slept in their own homes (29 bedrooms), which had central mechanical exhaust ventilation.

What changed. After a baseline week, the researchers covertly changed the exhaust-fan speed so each home spent a week at low, moderate and high ventilation, in balanced order. Participants weren't told when, or even whether, the setting changed.

What they found. In the 12 bedrooms where the three settings clearly changed CO₂, people had less deep sleep, more light sleep and more awakenings at the lower ventilation rates. Across the wider group of bedrooms with a clear difference between high and low, the one consistent finding was shorter deep sleep at low ventilation. Next-day thinking tests didn't differ.

Keep in mind. Real homes are messier than a lab: fewer than 1 in 10 people invited responded, the fan changes made a clear CO₂ difference in only some homes, and humidity rose along with CO₂.

Earlier work

• Strøm-Tejsen et al. (2016), in Indoor Air, raised the outdoor air supply to students' own dormitory bedrooms. With more fresh air, the students slept better by wrist-tracker measures, felt less sleepy the next day and did better on a logical-thinking test.
• Sekhar et al. (2020), in Building and Environment, compared field measurements of bedroom air from around the world with international ventilation standards, across seasons and regions. It also pointed out how few studies had linked bedroom air to sleep at that point, which is part of what the 2025 review set out to fix.
• ASHRAE's 2022 issue brief on bedrooms summarized what a few studies suggested at the time: sleep wasn't affected when ventilation kept CO₂ below about 750 ppm, could be disturbed around 1,150 ppm, and above about 2,600 ppm next-day performance could also suffer. Citing another recent review, it noted measured bedroom averages ranging from about 430 to 2,600 ppm, and called for bedroom-specific guidance.

What the research doesn't show

• That CO₂ itself is the cause. Most studies changed the ventilation, so CO₂ rose along with everything else people breathe out and give off. ASHRAE's 2025 position document calls the evidence for direct effects of CO₂ at everyday indoor levels "inconsistent." Either way, the fix is the same: more outdoor air.
• Big effects in a single night. The differences are minutes of wakefulness and a few percent of sleep efficiency or deep sleep. They're worth attention because a bedroom's ventilation is the same night after night, though no study has yet tracked whether the effects build up over months.
• That everyone is affected the same. Most participants were young and healthy. Children, older adults and people with health conditions were rarely studied.
• A sharp line. The 800 goal includes a margin. A night at 820 isn't meaningfully different from one at 790; a room that routinely averages 1,100 is.
• That lower is always better. Outdoor air is about 425 to 430 ppm, so no bedroom with people in it reads that low, and the studies didn't test whether going well below 750 helps further.

What it means for your bedroom

1. Measure a few ordinary nights. The app scores each one by its average while you slept, the same measure these studies use.
2. If the room averages 800 or less, you're there. Check again when the seasons change.
3. If it's above 1,000, it's worth fixing. Start with a free change for one night.
4. If free changes don't get you there, a ventilation system that supplies the bedroom can. Getting a bedroom to 800 explains how much air that takes and what to ask an installer.