Advisory on CO2 Monitoring to Assess Ventilation Adequacy

First released on June 2022

1. Introduction
This Advisory Note guides premises managers on how carbon dioxide (CO2) monitoring can be used as a proxy for ventilation adequacy, so that premises managers can take timely mitigating measures when ventilation is poor (when CO2 levels are above 800ppm). Measures to improve ventilation in indoor spaces can be found in the NEA | Updated Guidance Note on Improving Ventilation and Indoor Air Quality in Buildings for a Healthy Indoor Environment.

2. Prioritisation of premises for CO2 monitoring and ventilation improvements
As Singapore transitions to COVID-19 endemicity, premises managers should take active steps to ensure good ventilation, especially in enclosed, air-conditioned indoor environments. Good ventilation reduces the amount of virus aerosols and other indoor air pollutants that could be present. This will help mitigate the risk of aerosol-based transmission to protect the health of occupants, workers and general public in these premises. Measures to improve ventilation will also enhance our resilience against new COVID-19 variants of concern and future airborne infectious disease threats.

Ensuring good ventilation is critical in premises with higher risk of aerosol transmission, due to risk factors such as mask-off or bioaerosol-generating activities, prolonged time duration spent by occupants within the space, and/or the presence of vulnerable populations. A list of such higher risk premises is shown below. Managers of such premises should proactively ensure that these premises are always well-ventilated.  

List of premises with higher risk of aerosol transmission and/or presence of vulnerable group 
  • Hospitals and clinics
  • Eldercare facilities, including nursing homes and day activity centres
  • Establishments with food and drinks served on-site*
  • Gyms and fitness studios
    *Include food establishments, event venues, function rooms, nightlife establishments, karaoke establishments etc.

CO2 monitoring can be used as a quick, easy-to-implement proxy for ventilation adequacy, and to identify pockets of under-ventilated spaces or overcrowding within the premises. High CO2 levels imply that there is insufficient outdoor air intake and/or overcrowding, and measures should be taken to improve ventilation or reduce occupancy. Managers of higher risk premises should carry out CO2 monitoring regularly and take prompt action to improve ventilation, where necessary.

For more information, please refer to appended Guide to Premises Managers on CO2 Monitoring.



Use a non-dispersive infrared (NDIR) portable CO2 meter or install CO2 monitors (NDIR) with real-time display, depending on your operational needs.

[Note: Refer to Annex for recommended specifications of CO2 meters]

  • Measure at spaces with highest occupant density.
  • Place CO2 meters between 75cm and 120cm from the floor and as close as possible to the occupants’ breathing zone level, away from windows, doors or supply air vent where practicable.
  • Position CO2 meters at least 0.5m away from any human occupant where practicable, as exhaled breath contains CO2, which may influence the readings and give rise to misleading measurement.
  • To better identify locations with poorer air flow, take measurement from multiple locations within the space.

Crowds Sampling Points

  • Measure CO2 levels over a period of 5 min per sampling location.
  • The average CO2 level over the measurement period serves as a quick assessment of ventilation adequacy.
  • Take measurements during peak occupancy, or at timings that are deemed to be representative of the premises’ activity. Instantaneous or ‘snapshot’ readings can be misleading, so several measurements should be taken throughout the day. The frequency of measurements should be sufficient to ensure that changes in the use of the space throughout the day are represented in the readings.

Note: Some CO2 meters can auto-calculate and display the average CO2 reading over measurement period

It is recommended to keep the CO2 levels below 800 ppm over the measurement period in enclosed air-conditioned spaces. If the CO2 levels are above 800ppm[1], premises managers should assess the situation and take the necessary measures to improve ventilation.

[1] The indoor COlevels should ideally not exceed 800 ppm in the context of COVID-19, and under no circumstance should they exceed the SS554:2016 (Singapore Standard SS554: 2016 Code of Practice for Indoor Air Quality for Air-Conditioned Buildings) recommended limit of not more than 700 ppm in excess of outdoor levels, which is approximately 1,100 ppm.

Note: Localised air cleaning will not improve ventilation in indoor space but can help to reduce spread of diseases by removing virus aerosols.



(1) Recommended Specifications for CO2 Meters

✔️ Non-dispersive infrared (NDIR)

✔️ Able to measure between 300 to 3,000ppm or more

✔️ Logging frequency of at least once every minute

✔️ Accuracy of not more than ±50 ppm or ±5% (measured within the specified measurement range)

✔️ Resolution of 10ppm or less

✔️ Can be calibrated

✔️ [Good to have] Provide average readings based on selected measurement duration

(2) References

(A) Guidance Note on Improving Ventilation and Indoor Air Quality in Buildings amid the COVID-19 Situation

(B) Technical Advisory on Use of Air-Cleaning Technologies to Mitigate COVID-19 Aerosol Transmission Risk

(C) List of Portable Air Cleaners Against COVID-19 Virus Aerosols