HSE writes that a single snapshot can mislead and that persistently above 1500 ppm indicates poor ventilation. RevK’s closed home office climbed from about 430 ppm at 09:00 to 1000 ppm after 14:00 with one person. A 1200 ppm screenshot can sit on the way up. Those published series are not AirMeasure UK rooms, and 1500 ppm is not a medical exposure limit.
What HSE already wrote
The HSE carbon-dioxide page asks for several readings through the day, with occupancy and ventilation noted. Persistently above 1500 ppm is written as a sign that ventilation is poor. The eight-hour workplace exposure limit is a different number on a different document. The 1500 ppm line is a ventilation action, not a diagnosis, and not a home health standard. In a room that has an air cleaner, HSE writes that carbon dioxide does not represent ventilation.
What the published climbs look like
RevK logged a British 5 m × 5 m home office, window shut, door shut: one person, about 430 ppm at 09:00, 1000 ppm after 14:00, a dip when the door opened for a delivery, and no plateau that day. Bedroom nights exceeded 1300 ppm. A window blocked by a curtain barely dropped the number. Geerling’s basement office sat near 900 ppm with the vent open and passed 3000 ppm after hours with it closed. His 2025 note, without a laboratory reference, recorded more than 2300 ppm with 15–20 people in a room.
Those curves belong to their authors. They show why a single 1200 ppm screenshot is not “the room”. This publication has not published a room series of its own, so it does not say any UK living room, bedroom or classroom needs a window opened.
Schools are a different pack
SAMHE publishes classroom minute-level records for participating schools. Building Bulletin 101 is the official school-building ventilation document. Those are research and design sources. They are not rewritten here as a domestic rule. This publication has not published a school series.
Sources and scope
Sources checked on 23 September 2026. Numbered references point to the original publishers. Their sample measurements are not AirMeasure UK measurements. Manufacturer, tutorial and official material is identified separately.
- HSE, Using CO2 monitors ↗UK workplace ventilation page. Prefers NDIR on a portable device; head height; more than 50 cm from people; away from doors, windows and supply vents. A single snapshot can mislead. Persistently above 1500 ppm is written as a sign of poor ventilation. In a room with an air cleaner, carbon dioxide does not stand in for ventilation. Workplace guidance, not a home health standard and not an instrument certificate.
- RevK, Air quality and CO₂ levels ↗Adrian Kennard, 20 March 2019. British engineer’s home-office and bedroom logs. A closed 5 m × 5 m office rose from about 430 ppm at 09:00 to 1000 ppm after 14:00 with one occupant. Bedroom nights exceeded 1300 ppm. Outdoor air was written as 430–560 ppm. Those rooms are his. They are not AirMeasure UK measurements.
- RevK, Understanding CO₂ air quality better ↗Same author, 21 March 2019. Cooking sent particles “off the scale” and also raised carbon dioxide. A curtain-blocked window barely dropped the bedroom reading. The author questions treating a weekly minimum, or outdoor air, as a 400 ppm zero.
- Jeff Geerling, Monitoring my home’s air quality with AirGradient DIY ↗8 September 2021. Lists SenseAir S8, Plantower PMS5003 and SHT30. A basement office sat near 900 ppm with the vent open and passed 3000 ppm after hours with it closed. Case heat raised temperature and humidity. Automatic baseline calibration was written as needing about two weeks, during which carbon dioxide could read about 200 ppm high. Those figures are the author’s.
- Jeff Geerling, Air Lab is the Flipper Zero of air quality monitors ↗21 November 2025. The author states there was no laboratory reference instrument. An Air Lab (SCD41) differed from several AirGradient units by about 50–100 ppm. A gathering of 15–20 people exceeded 2300 ppm. Recirculating car air reached 1500–2000 ppm. The sample is disclosed as supplied. Not a UK house and not an AirMeasure UK test.
- SAMHE, About the project ↗UK school research project. Classrooms record minute-level carbon dioxide, PM2.5, TVOC and temperature. The project is a research network, not a monitor-buying guide. Low-cost TVOC in that network is not a reference VOC measurement.
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