Bedroom overnight: the CO₂ climb you sleep through

A sleeping adult exhales about 11 liters of CO₂ per hour (Fan et al. measured 11.0 ± 1.4 L/h). In a 35 m³ bedroom (a typical small-to-medium room) with the door closed and no mechanical ventilation, that output climbs steadily through the night. At the air-change rates common in closed bedrooms, about 0.3 to 0.5 per hour (a study of 500 Danish children's bedrooms found a geometric mean of 0.46), a one-person bedroom reaches roughly 1,050–1,350 ppm by 7 AM and a two-person bedroom roughly 1,650–2,300 ppm; a child's room with the door shut tight can read higher still relative to room volume.

Xu et al. and Mishra et al. have documented that higher bedroom CO₂ goes with measurably worse sleep: longer time to fall asleep, less slow-wave sleep, and lower self-rated sleep quality. Whether CO₂ is the cause or a marker for poor ventilation (which carries other consequences) is still debated; either way, the intervention is the same.

The overnight shape is characteristic: a steady CO₂ climb that starts after bedtime, peaks just before waking, and drops sharply when the door opens. Humidity tracks alongside (sleeping adults exhale water vapor too). VOCs and PM stay flat. Terrestream does not work out which room is a bedroom from this shape: you choose the room type when you set up the sensor, and in a bedroom it tells you when CO₂ runs high during the night or stays elevated across it.

Practical responses, ordered roughly by cost: leave the bedroom door open if pets and household allow (single largest intervention); crack a window an inch; run a quiet bedroom HRV/ERV (the ~$300 trickle-ventilation units do enough); install whole-house ventilation per ASHRAE 62.2.