What Counts as a Healthy CO₂ Level at Home, and How to Track It

If you’ve bought a CO₂ monitor, you’ve probably watched the number climb in a closed bedroom overnight and wondered whether it matters. Here’s what the main guidelines say, where the often-quoted 1,000 ppm comes from, and how to keep track of the air at home without guessing.

This article is general information, not medical advice. If you have symptoms you’re worried about, talk to a health professional.

What the Number Means

CO₂ concentration is measured in parts per million (ppm): 1,000 ppm means 0.1% of the air is carbon dioxide. Outdoors, the global average is now about 425 ppm, and rising by a few ppm a year, according to NOAA’s measurements.

Indoors, the main source of CO₂ in most homes is people breathing out (gas stoves and other combustion add some too). So when a room’s CO₂ rises well above the outdoor level, it usually means the air isn’t being replaced fast enough for the number of people in it. That’s why CO₂ is widely used as a sign of ventilation: ASHRAE, the body that writes North America’s main ventilation standard, describes indoor CO₂ as an indicator of how much outdoor air a space gets relative to its occupants, not as a complete measure of indoor air quality.

What the Guidelines Say

Different organizations answer different questions, which is why the numbers you see vary.

Source	What it says	What it’s for
Health Canada (2021)	A long-term exposure limit of 1,000 ppm, averaged over 24 hours, in homes	Reducing the risk of symptoms such as headaches, tiredness, and eye irritation, and lower performance on tasks, seen in studies of schools and offices
ASHRAE Standard 62.1	No indoor CO₂ limit. An old 1,000 ppm figure was removed from the standard because it was so often misread as a health limit	Designing ventilation for buildings
WHO indoor air quality guidelines (2010)	No guideline value for CO₂; they cover pollutants like carbon monoxide, nitrogen dioxide, formaldehyde, benzene, and radon	Health-based limits for specific indoor pollutants
OSHA (United States)	A workplace limit of 5,000 ppm averaged over an 8-hour shift	Occupational safety for healthy adult workers, not comfort at home

So for a home in Canada, the clearest official reference is Health Canada’s: keep the 24-hour average under 1,000 ppm. Note that it’s an average. A bedroom that reaches 1,400 ppm by morning, with the door closed, and falls back during the day may still average under it, or may not; only a full day’s readings can say.

What’s Less Certain

Some studies have found that people make worse decisions in rooms with higher CO₂, at levels between 1,000 and 2,500 ppm; others haven’t found the same effect when CO₂ alone is raised. ASHRAE’s position document reviews these studies and describes their results as inconsistent. One reason the results differ: in a poorly ventilated room, CO₂ rises together with everything else people and furnishings give off, so it’s hard to separate CO₂’s own effect from that of the stale air it signals.

The practical reading of all this: a high CO₂ reading is a good reason to ventilate, whether or not CO₂ itself is the problem.

Measuring It Properly

• Use a monitor with a real CO₂ sensor. Look for NDIR (non-dispersive infrared) or photoacoustic sensors. Many cheap “air quality” monitors show an eCO₂ or “equivalent CO₂” number estimated from other gases; it can be far from the real value.
• Put it where you breathe, about head height, away from windows, vents, and your face. Right beside your pillow, it can pick up your own breath rather than the room’s air.
• Mind calibration. Some NDIR monitors calibrate themselves against fresh outdoor air from time to time. Your monitor’s manual says how; airing the room fully now and then helps.
• Look at the pattern, not one reading. CO₂ swings with who’s home, doors, and windows. The daily average and the overnight peak tell you more than any single number.

Tracking It in Kaizora

Kaizora keeps your monitor’s readings next to everything else you track, and turns them into the air you breathed.

1. Import your monitor’s history. Today Kaizora imports the Aranet4’s CSV export from the Aranet Home app; you say which device it was and where it was. Readings from any other monitor can be logged by hand on the Air Quality page, with their position. See Importing From an Aranet4 Monitor.
2. Add your location history, from Google Maps Timeline or by turning on tracking. Wherever you were, Kaizora takes the newest reading within 100 m in the hour before as your CO₂ Concentration at that moment, so a reading from your bedroom monitor doesn’t count while you’re at work.
3. Set a habit of “CO₂ Concentration at most 1,000 ppm a day, on average”, which checks each day’s average against Health Canada’s figure. Keep in mind it averages the values at your location fixes, which is close to, but not the same as, a true 24-hour average. See Habits.
4. Add a reference range on CO₂ Concentration, for example a mild band above 1,000 ppm, so high readings are flagged on your chart and on Home. A flagged single reading isn’t the same as exceeding a 24-hour average; it’s a nudge to open a window. See Reference Ranges.
5. Compare it with Time Asleep, or with how rested you feel, on the Correlations page. Moving together doesn’t prove one causes the other, but it’s a good question to ask.

The Short Version

• Outdoor air is about 425 ppm; indoors, more people and less fresh air push it up.
• Health Canada’s guideline for homes is a 1,000 ppm average over 24 hours. ASHRAE and the WHO set no CO₂ limit for homes; 5,000 ppm is a workplace limit.
• Use a real NDIR sensor, place it well, and watch the daily pattern.
• When it’s high, ventilate.

Sources

• NOAA Global Monitoring Laboratory, Trends in Atmospheric Carbon Dioxide. The global mean for 2025 was about 425.6 ppm; check the page for the latest value.
• ASHRAE, Position Document on Indoor Carbon Dioxide (2022, revised 2025).
• Health Canada, Residential Indoor Air Quality Guidelines: Carbon Dioxide (2021).
• World Health Organization, WHO Guidelines for Indoor Air Quality: Selected Pollutants (2010).
• US Occupational Safety and Health Administration, 29 CFR 1910.1000, Table Z-1.