Why does the bedroom feel stuffy by morning? Open the window and see

Floor area 12 m²

Ceiling height 2.5 m

Sleepers

Window

Bedroom door

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CO₂ by 07:00 (ppm)

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Hours above 1,000 ppm

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Assumed air changes per hour

Model: CO₂ rises by about 10 litres an hour per sleeper, spread through the room, and fresh air at about 420 ppm replaces part of it each hour. Starting level 600 ppm at 23:00. Air-change values (closed room 0.3, tilted window +1.5, wide open +4, door ajar +0.5) are rough assumptions for illustration.