Bedroom CO₂ Overnight: A Practical Measurement Log
If you want to investigate bedroom ventilation, a full overnight record is more useful than one morning reading. Record the conditions as well as the numbers so you can make a meaningful comparison.
Before the first night
Use a monitor that measures CO₂ directly, and follow the manufacturer’s placement and calibration instructions. Choose a consistent position away from direct exhaled breath or an inlet jet. Note the model and whether the record is measured CO₂ or an estimated value.
What to record
| Item | Your record |
|---|---|
| Date and room | Keep the same room for a comparison |
| Occupancy | Number of people and occupied hours |
| Doors and windows | Open, closed or changed during the night |
| Ventilation | Equipment and operating settings |
| CO₂ history | Bedtime, overnight trend and morning |
| Other conditions | Changes in weather, routine or equipment |
We suggest repeating the log over several nights. Keep the original data and annotate changes rather than comparing the highest number from one night with the lowest from another.
What the log can tell you
Use the pattern to frame questions about outdoor-air supply and distribution. It does not diagnose a sleep problem or tell you how many hours of sleep were lost. Evidence for direct effects at commonly observed CO₂ concentrations is inconsistent; see ASHRAE’s position document.
What to change and compare
If the room needs a ventilation assessment, show the installer your floor plan, log and normal door positions. Agree one practical change at a time and repeat the measurement. Consider outdoor pollution before changing window-opening habits; investigate particles separately using our PM2.5 guide.
For a general explanation of CO₂ readings, read CO₂ levels in the bedroom. For system planning, see the technical note and pricing.
FAQ
Does opening a window solve it?
Sometimes. It works on low-AQI nights and in a city with clean outdoor air. In Delhi NCR in winter, an open window brings the CO₂ down but lets the outdoor PM2.5 in.
Does an air purifier reduce CO₂?
No. HEPA filters and activated carbon do not capture CO₂. Only ventilation (fresh outdoor air mixing in) lowers it.
Why didn’t I notice this in my parents’ house?
Old homes leak air through gaps. New homes don’t. The sealing improvement is what surfaced the CO₂ problem.
Is 1,400 ppm dangerous?
Not acutely. Submarine crews work at 5,000–8,000 ppm. Studies of direct effects at the levels usually seen in bedrooms are inconsistent. Read a high overnight number as a sign that the room is getting too little fresh outdoor air.
Where does aqi0 keep my bedroom CO₂?
With the bedroom door open even an inch, CO₂ stays under 1,000 ppm overnight with two to three people in the room.