Why 800 ppm? The bedroom CO₂ goal, and where 1,000 comes in

HouseExhale puts every night on one scale built around that goal:

Where 800 comes from

In 2025, a team led by Mizuho Akimoto at Waseda University, with researchers from the Technical University of Denmark and Shanghai Jiao Tong University, published a review for ASHRAE, the engineering society that writes the main US ventilation standards. The project, ASHRAE research project 1837-RP, pulled together 17 studies with 22 sets of experiments on bedroom ventilation and sleep.

Three numbers came out of it:

• 1,000 ppm. The lowest CO₂ level at which sleep was disturbed in those studies, in other words the best-ventilated condition that still affected sleep, was about 1,000 ppm.
• 850 ppm. The highest level at which no effect on sleep was seen. The reviewers didn't treat it as a firm "no effect" line, because of sensor accuracy and the need for a safety margin.
• 800 ppm. Their recommended ceiling for bedrooms.

Holding a bedroom at 800 takes about 8 liters per second of outdoor air for each person sleeping there, roughly 17 cubic feet per minute (cfm). The reviewers note that's at least twice what many current home ventilation standards provide. Field studies find many bedrooms, including in new, airtight homes, well above 1,000 ppm with the door shut. How to get a bedroom to 800 covers what that means in practice.

Where 1,000 comes in

The review's 1,000 ppm line matches what individual experiments found. In one of the most careful, Kang and colleagues (2024) had 36 healthy young adults sleep two nights at each of three ventilation levels, with average bedroom CO₂ of about 750, 1,000 and 1,300 ppm. Compared with 750:

• at 1,000 ppm, sleep efficiency fell by 1.3% and people spent about 5 more minutes awake;
• at 1,300 ppm, sleep efficiency fell by 1.8%, time awake rose by about 8 minutes, deep sleep shortened, and a stress hormone (cortisol) rose.

The authors' advice was to avoid bedroom ventilation that lets the average reach 1,000 ppm or more. A smaller study by Wang and colleagues (2023) found the same direction: as the average went from 680 to 920 to 1,350 ppm, the share of deep sleep fell from about 20% to 17% to 14%.

These effects are modest on any one night: minutes, not hours. 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. The research behind the goal walks through these and other studies, including what they can't tell you.

Why the average, not the peak

The studies describe each night by its average CO₂ over the hours people slept, so HouseExhale does too. The peak is one moment, usually just before you wake. The average reflects the whole night you actually breathed.

• A recorded night (an Aranet4's memory, a SwitchBot heard by your phone, or a CSV export) counts its average while you were asleep, weighted by time so a burst of fast readings doesn't count extra.
• A night you type in counts the overnight high, because that's what most monitors show at a glance. It's always at or above the average, so a typed night never makes a room look better than it is. If your high is 800 or less, the whole night met the goal.

Across nights, the app takes the median, the middle value, as your typical night. One odd night doesn't pull it around.

The same fresh air, a lower number

If you've seen 1,000 ppm called the line for "good" ventilation, you're not wrong, and the two numbers fit together. ASHRAE's position document on CO₂ says a reading under 1,000 ppm is at best an indicator of about 8 L/s of outdoor air per person (ASHRAE rounds it to 16 cfm), a relationship based on the typical CO₂ output of seated, awake adults. Asleep, people breathe out less CO₂. So the same 8 L/s per person that keeps an office near 1,000 keeps a bedroom near 800.

In other words, the 800 goal isn't a stricter idea of clean air. It's the same amount of fresh air per person, measured in a room where people breathe out less CO₂.

Other numbers you'll see

• Aranet4's colors. By default the light is green below 1,000, yellow to 1,400 and red above. That's fine for a living room during the day, but green doesn't mean a bedroom met the 800 goal. In the Aranet Home app you can set your own levels (settings wheel, CO₂ indication mode, Custom); yellow at 800 and red at 1,000 matches HouseExhale.
• CDC NIOSH mentions CO₂ below 800 ppm as one potential target for good ventilation, with the caveat that one number may not suit every space.
• The UK Health and Safety Executive says levels consistently over 1,500 ppm in an occupied workplace mean ventilation needs improving. That's an "act now" line for offices, not a goal for bedrooms.
• Workplace safety limits are far higher: OSHA's limit for an 8-hour workday is 5,000 ppm. Even poorly ventilated bedrooms in field studies average well below that, at most around 2,600 ppm.

What the goal is, and isn't

At these levels, CO₂ isn't a poison. ASHRAE calls the evidence for direct effects of CO₂ itself at everyday indoor levels "inconsistent," and the review behind the 800 goal treats CO₂ as a stand-in for ventilation rather than as the culprit. A room with high CO₂ is also a room where everything else people breathe out and give off builds up. Researchers still debate how much of the sleep effect comes from the CO₂ and how much from the rest of the stale air. For your bedroom, the practical answer is the same either way: more outdoor air.

So a Stuffy night doesn't mean anything is wrong with you, and a Fresh night doesn't mean the air is free of other pollutants. The number tells you how well the room is ventilated for the people sleeping in it, against a goal grounded in sleep research. Still have questions? Try bedroom CO₂ questions and answers.