Office CO₂ monitoring & carbon dioxide testing

Office CO₂ monitoring is the single most cost-effective intervention available to a facilities team. Indoor CO₂ above ambient is generated almost entirely by people breathing, and the rate at which it rises and falls is a direct proxy for how effectively outdoor air is being supplied to occupied zones. Two CO₂ sensors and a fortnight of data tell you more about a building's real ventilation performance than a year of complaint logs.

Above 1000 ppm, measurable declines in concentration and decision-making appear. Above 1500 ppm, occupant complaints multiply. The Harvard COGfx studies recorded an 11% improvement in cognitive scores when meeting-room CO₂ fell from 1400 to 600 ppm — an effect size large enough to matter to any knowledge-work organisation.

We use NDIR sensors with ±30 ppm accuracy, deployed at desk and breathing-zone height across a representative sample of open-plan workspace, meeting rooms and shared areas. Sensors are wireless, mains or battery powered, and stream data to a secure cloud dashboard. A typical office floor needs 6–12 sensor locations to characterise ventilation effectiveness reliably.

Where the AHU has built-in CO₂ control, we add reference sensors at the breathing zone to verify that the control signal matches what occupants actually experience — they often do not.

A healthy office shows CO₂ that stays below 1000 ppm during steady-state occupancy, with peaks in meeting rooms that fall away quickly when the room empties. The shape of the curve matters as much as the headline number — a slow morning rise that plateaus around lunchtime, then climbs again to a 4pm peak, is the classic signature of under-sized ventilation in a building running fixed-schedule supply against hybrid occupancy.

We benchmark every zone against BS EN 16798-1, CIBSE TM40 and WELL Air thresholds, then make a specific recommendation: rebalance, recommission, upgrade to demand-controlled ventilation, or hold and re-measure.

One-off CO₂ spot tests have their place — typically as part of a wider office air quality survey — but continuous monitoring is now the operational norm. Twelve months of CO₂ data gives facilities teams the evidence to defend ventilation upgrades to finance, satisfies WELL Performance Verification, and provides the live dashboards tenants increasingly expect at lease renewal.