The Link Between Bedroom CO2 and Sleep
Most people never think about the air they breathe while sleeping, yet research consistently shows that elevated CO2 levels in the bedroom significantly degrade sleep quality. A 2015 study published in Indoor Air found that participants sleeping with CO2 below 800 ppm reported better next-day focus, fewer awakenings, and deeper sleep stages compared to those in rooms above 1,200 ppm.
Why CO2 Rises Overnight
A sleeping adult exhales roughly 200 mL of CO2 per minute. In a closed bedroom of 25 square metres with no ventilation, CO2 can climb from 420 ppm to well over 2,000 ppm by morning. The smaller the room or the more people (and pets) sharing it, the faster levels rise.
What the Research Says
- Below 600 ppm — Optimal for restorative sleep. Hard to achieve without mechanical ventilation or an open window.
- 600-1,000 ppm — Acceptable. Most people sleep well in this range.
- Above 1,000 ppm — Sleep efficiency drops. You may wake feeling groggy despite eight hours in bed.
- Above 2,000 ppm — Headaches and poor concentration the next day become likely.
A Danish Technical University study found that lowering bedroom CO2 from 2,400 ppm to 800 ppm improved participants self-reported sleep quality by 60 percent and next-day cognitive performance by 12 percent.
Practical Steps to Better Sleep Air
- Monitor your bedroom — place a CO2 monitor on your nightstand. Our best home monitors guide covers great options.
- Crack a window — even a 5 cm gap provides enough airflow to halve CO2 levels overnight.
- Use a timed fan — a quiet fan pointing toward a cracked door improves air exchange without noise disruption.
- Consider an ERV — an energy recovery ventilator supplies fresh air without losing heating or cooling. Learn more in our ERV vs windows guide.
- Set alerts — some monitors can trigger automations when CO2 exceeds a threshold. See how to set up CO2 alerts.
Use the CO2 calculator to estimate how quickly your bedroom CO2 rises based on room size and occupancy.