Why CO₂ matters at home
Indoor CO₂ levels track how well a room ventilates against the number of people in it. A bedroom with the door and window shut overnight can climb from outdoor (around 420 ppm) past 2,000 ppm by morning. Studies have linked CO₂ above 1,000 ppm to reduced cognitive performance and disrupted sleep — particularly relevant for bedrooms, home offices and small meeting rooms.
Unlike PM2.5 or VOCs, CO₂ does not lie. It rises predictably with occupancy and falls predictably with ventilation. Treat it as your ventilation gauge, not a contaminant level.
Unlike PM2.5 or VOCs, CO₂ does not lie. It rises predictably with occupancy and falls predictably with ventilation. Treat it as your ventilation gauge, not a contaminant level.
What to look for in a home CO₂ monitor
Five things matter: (1) true NDIR CO₂ measurement (not eCO₂ derived from VOC); (2) documented accuracy (better than ±50 ppm + 5%); (3) calibration paperwork; (4) at least 1-minute logging resolution; and (5) the ability to export the data so you can verify it against another source.
Avoid devices that only show a coloured indicator without a numerical CO₂ value. Avoid vendor marketing that uses 'eCO₂' without explaining it — eCO₂ is estimated from VOC chemistry and is unreliable in bedrooms (where the human-CO₂-correlation is broken by sleep-related VOCs).
Avoid devices that only show a coloured indicator without a numerical CO₂ value. Avoid vendor marketing that uses 'eCO₂' without explaining it — eCO₂ is estimated from VOC chemistry and is unreliable in bedrooms (where the human-CO₂-correlation is broken by sleep-related VOCs).
What good and bad CO₂ looks like
Below 800 ppm: good ventilation. Outdoor air is around 420 ppm in 2026 — every 100 ppm above that is mostly your breath plus the room's other occupants.
800–1,000 ppm: acceptable. Most rooms with people in them sit here.
1,000–1,500 ppm: consider opening a window or running mechanical ventilation. UK Department for Education guidance suggests classroom CO₂ should stay below 1,500 ppm on average across an occupied period.
1,500–2,000 ppm: clear ventilation problem. Drowsiness and reduced cognitive performance documented at these levels.
Above 2,000 ppm: open windows or leave the room. Common in closed bedrooms by morning, packed meeting rooms, and small podcast booths.
800–1,000 ppm: acceptable. Most rooms with people in them sit here.
1,000–1,500 ppm: consider opening a window or running mechanical ventilation. UK Department for Education guidance suggests classroom CO₂ should stay below 1,500 ppm on average across an occupied period.
1,500–2,000 ppm: clear ventilation problem. Drowsiness and reduced cognitive performance documented at these levels.
Above 2,000 ppm: open windows or leave the room. Common in closed bedrooms by morning, packed meeting rooms, and small podcast booths.
Where to put a CO₂ monitor at home
Start with the bedroom — overnight CO₂ exposure dominates daily dose for most people. Second priority is wherever you do your most concentrated work (study, home office). Third is the room you cook in, because CO₂ is a good ventilation gauge there even though the actual cooking pollutant of concern is PM2.5.
Mount the device at head height where you spend time. Avoid placing it directly in the airflow from an air conditioner or open window — you want room-average, not the supply side of the duct.
Mount the device at head height where you spend time. Avoid placing it directly in the airflow from an air conditioner or open window — you want room-average, not the supply side of the duct.
How Envora One helps
Envora One uses true NDIR CO₂ measurement (±30 ppm + 3% of reading) alongside ten other channels — so the same device that watches your overnight CO₂ also watches PM2.5 from cooking, humidity for mould risk, and VOCs from cleaning chemistry.
Readings stream to a dashboard, expose over MQTT and REST, and history is retained for 3 years on the free Home plan. No subscription. See the product or buy direct for £249.
Readings stream to a dashboard, expose over MQTT and REST, and history is retained for 3 years on the free Home plan. No subscription. See the product or buy direct for £249.