Bedroom CO₂: questions and answers

Short answers to the questions people ask most about CO₂ in bedrooms. The goal behind all of them: 800 ppm or less, on average, while you sleep.

What CO₂ level should my bedroom be at night?

800 ppm or less, on average, while you sleep. That's the level a 2025 review of 17 sleep studies for ASHRAE recommends for bedrooms. HouseExhale calls a night at or under 800 Fresh, 801 to 999 Building up, and 1,000 or more Stuffy. Why 800, and not 1,000 explains where each number comes from.

Why 800 and not 1,000?

In the studies the review pulled together, the lowest CO₂ level at which sleep was disturbed was about 1,000 ppm, and no effect showed at 850 or below. The reviewers set the goal at 800 because of sensor accuracy and the need for a safety margin. 1,000 is where problems start, not a target to aim at. The research, study by study.

Is 1,000 ppm dangerous?

Not in the way a poison is. Workplace safety limits for CO₂ are 5,000 ppm over an 8-hour day, and even poorly ventilated bedrooms in field studies average well below that. What 1,000 ppm tells you is that the room isn't getting much fresh air for the people in it. In one controlled study, people spent about 5 more minutes awake and had slightly lower sleep efficiency at 1,000 than at 750. Small on one night, and worth attention because a bedroom's ventilation is the same night after night.

Why does HouseExhale score the average instead of the highest reading?

Because that's what the sleep studies measured: the average CO₂ over the hours people slept. The highest reading is a single moment, usually just before you wake. When your monitor records the whole night, the app averages it, weighted by time, so it matches the research. How each night gets its number.

My monitor only shows the highest reading. Can I still use it?

Yes. Type the overnight high each morning and the app scores it against the same goal. The high is always at or above the average, so a typed night never flatters the room. If your high is 800 or less, the whole night met the goal. If it's a bit over, the real average was probably lower, and a monitor that records the night, like an Aranet4, will show by how much.

My Aranet4 shows green. Doesn't that mean the air is fine?

Its light stays green up to 1,000 ppm by default, yellow to 1,400 and red above. That's a reasonable daytime scale, but green isn't the same as meeting the 800 bedroom goal. In the Aranet Home app you can change the levels (settings wheel, then CO₂ indication mode, then Custom). Yellow at 800 and red at 1,000 matches HouseExhale. The light reacts to the reading right now, so expect it to turn yellow late in a night that still averages under 800.

How much fresh air does a bedroom need to stay at 800?

About 8 liters per second, or 17 cfm, of outdoor air for each person sleeping there, delivered while they sleep. Two people need about 34 cfm. The review notes that's at least twice what many home ventilation standards provide. Getting a bedroom to 800 shows what that means for your home.

Why is my bedroom fine when I sleep alone but not with my partner?

CO₂ comes from the people breathing in the room, so two people produce about twice as much. The same trickle of fresh air that holds one sleeper under 800 can leave two well above it. That's also why a fair comparison keeps the same people in the room on every night you compare.

Is leaving the door open enough?

Sometimes. An open door connects the bedroom to the rest of the house, which helps most when the rest of the house is itself well ventilated. In one study of new homes in Scotland, bedrooms with the door open but windows shut still averaged about 1,550 ppm. Fire-safety researchers also recommend sleeping with the door closed. Test it for a night and see. Free fixes to try first.

Can I reach 800 without an HRV or ERV?

Often, yes: a window cracked, an existing ventilation system run on boost or continuously, or one fewer person in the room can all get there. The question is whether you can keep doing it every night, in every season. A balanced system that supplies the bedroom does it with the door and window shut. Measure first, then decide.

Is lower always better? Should I aim for 400?

You can't get there with people in the room: outdoor air itself is about 425 to 430 ppm. The studies compared bedrooms near 750 with bedrooms at 1,000 and above; they didn't test whether going much lower helps further. Getting under 800 is the goal; pushing far below it mostly costs energy and noise.

Is it the CO₂ itself that disturbs sleep?

Researchers don't fully agree. Most studies changed the ventilation, so CO₂ rose along with everything else people breathe out and give off, and ASHRAE calls the evidence for direct effects of CO₂ at everyday indoor levels "inconsistent." The review behind the goal treats CO₂ as a sign of ventilation rather than the cause. Either way, the fix is the same: more outdoor air.

How accurate does my monitor need to be?

Use a monitor that measures true CO₂ with an NDIR sensor, not an "eCO₂" estimate. Good ones are within about 50 to 90 ppm at 800: the Aranet4 lists ±(30 ppm + 3% of the reading) and the SwitchBot Meter Pro CO₂ ±(50 ppm + 5%). That's one reason the goal has a margin built in. A quick check outdoors, where it should read about 425 to 430 (a little higher near roads or the house), catches a monitor that's far off. Where to put your monitor.

Do building codes require 800 ppm in bedrooms?

No. US home ventilation standards set an airflow for the whole house rather than a CO₂ level for each room. ASHRAE 62.2, for example, works out a whole-house rate from floor area and the number of bedrooms. The 2025 review argues those rates may not be enough for bedrooms and that standards should be revisited. Meeting code and meeting the 800 goal aren't the same thing, so ask installers how much air each bedroom will get.

Does the goal change with the seasons?

The goal doesn't, but your room's number often does. In winter and in hot, humid summers, windows stay shut and the same bedroom can run higher. Recheck when the season changes; the app reminds you.

My bedroom averages over 1,000. What should I do first?

Measure two or three ordinary nights so you have a fair baseline, then try one free change for one night: the door open a few inches, your ventilation on boost, or a window cracked if conditions allow. If one gets you to 800 and you can keep doing it, you're done. If not, a ventilation system that supplies the bedroom is worth pricing, and your measurements make the quotes better. Run a fair three-night check.