Information for Using CO2 monitors

Is CO2 monitoring appropriate for your venue?

CO2 monitoring measures the ingress of outdoor air to dilute indoor sources of CO2. This gives a good indication of ventilation in spaces with high occupancy for long periods of time. It is particularly well suited to venues above 50m2  where customers stay for periods of 1 hour or more. Once spaces become very large (>320m2) then you are likely to need multiple monitors as the outdoor air may enter the space but not mix well across the whole area. 

Smaller venues or venues where customers only stay for short time periods are not well suited to CO2 monitoring. In these cases high readings can still highlight a need for improvement but low readings do not indicate adequate ventilation. 

Where there are significant sources of CO2 in the space the interpretation below cannot be used. Short duration releases of CO2 such as in confetti cannons are not an issue provided you account for them when viewing the results. Where there is significant combustion e.g. in kitchens, then CO2 monitoring will not be reliable. If you use theatrical smoke that is generated using CO2 over long time periods then CO2 monitoring is not recommended. 

Choosing a CO2 monitor

There are many different brands on the market. Below provides a few examples

Mounting your CO2 monitor

Interpreting your CO2 monitor

Firstly check your monitor is working correctly. Following a long period of zero occupancy, or when taken outside you would expect a reading of ~400PPM. CO2 monitors are known to drift over time so you should regularly check this.

Initially, attempt to measure your CO2 levels with your existing ventilation practices for a good period of time (a week at least). This will allow you to capture periods of low and high occupancy so that you can tailor any ventilation strategies to these times. It is particularly important to capture high occupancy periods to ensure your ventilation is adequate when your venue is full. 

Readings below 800 PPM indicate good air flow for the number of people in the space. Be aware of low CO2 readings that rise rapidly. These could indicate poor ventilation. If you observe readings over 1500 PPM then ventilation should be prioritised for improvement. There are some helpful tips below.

Other factors to check include:

If your readings are surprisingly high it is worth checking the results. Did you place the monitor where it catches someone's breath? Can you recheck the calibration by measuring outdoor concentrations. Perhaps do a trial with the monitor in a different location. 

Addressing CO2 readings above 1500 PPM

Short term

Medium term

Long Term

Further information on using CO2 monitors is available from the Health and Safety Executive which you can access via this link.