What CO2 level should I target in a UK office?

The recommended maximum CO2 concentration for occupied offices is 1000 ppm per CIBSE Guide A and the HSE Workplace (Health, Safety and Welfare) Regulations. Outdoor air is typically 400 ppm, so the indoor-outdoor differential should not exceed 600 ppm. Post-pandemic guidance recommends aiming for 800 ppm where possible, with ventilation boost activated at 800 ppm.

How many CO2 sensors do I need per room?

As a minimum, install one CO2 sensor per occupied zone. For open-plan spaces, use one sensor per 100 m² of floor area. Sensors should be mounted at breathing height (1.2-1.5m) away from windows, doors, and supply air diffusers. Each zone with independent ventilation control should have its own sensor.

What is demand-controlled ventilation (DCV)?

DCV uses CO2 sensors to modulate ventilation rates in real time based on occupancy. When CO2 rises (indicating more people), fan speeds or damper positions increase to provide more fresh air. When the space is lightly occupied, ventilation reduces, saving energy. DCV can reduce ventilation energy by 20-40% compared to fixed-rate systems.

Do I need CO2 data logging?

CO2 data logging is recommended for Building Regulations compliance evidence, TM44 air conditioning inspections, and WELL Building Standard certification. Logged data at 5-15 minute intervals helps identify ventilation issues and demonstrate ongoing compliance. Many modern sensors include cloud-based logging.

At what CO2 level should ventilation boost activate?

Ventilation boost should trigger at 800 ppm (80% of the 1000 ppm target) to prevent levels exceeding the maximum. This gives the ventilation system time to respond before occupants experience discomfort. A second alarm at 1500 ppm indicates a ventilation system failure that requires investigation.

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CO2 Monitoring Calculator — Sensor Placement & Ventilation

Calculate CO2 sensor requirements, target levels, and ventilation boost triggers for occupied spaces per CIBSE and HSE guidance.

Space Type

Determines target and alarm CO2 levels

Floor Area

Maximum Occupants

Number of Zones

Each zone with separate ventilation control

How We Calculate This

This calculator determines CO2 sensor requirements and ventilation rates needed to maintain safe indoor air quality levels per CIBSE Guide A and HSE guidance.

CO2 generation rates

Each sedentary person generates approximately 0.005 L/s of CO2 (CIBSE Guide A). Active people in gyms generate 2-3 times more. The required ventilation rate is calculated to dilute CO2 below the target concentration.

Sensor placement rules

Minimum 1 sensor per occupied zone
1 sensor per 100 m² in open-plan spaces
Mount at 1.2-1.5m height (breathing zone)
Away from windows, doors, and supply diffusers

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.