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CO2 Monitoring in Classrooms: Plain English Guide for Teachers


This guide is generic and should be appropriate for any classroom and CO2 monitor 


Why monitor CO2?

CO2 is a gas with a known background level, outside (roughly 420ppm that’s parts per million). We also breath out CO2 at a known rate, so between the amount of people breathing, the size of the space and the amount of outside air we bring in, we can use CO2 as a guide to tell us how well the ventilation is working. In the context of this pandemic but also for good general health and wellbeing, ventilation is an important part of reducing risk.


What is good and not good?

It is very hard for us as humans to feel what is good or bad air quality. We can, to a degree, feel if a room is uncomfortable or stuffy but it is hard to quantify.
If a room has a mechanical ventilation system that can deliver a defined volume of air, then it can be set to meet certain levels, that mean we usually don’t have to worry about it.
Most classrooms however rely on windows for ventilation and that requires us to manage them and react to changes in the forces (weather) that drives how much air comes in, by adjusting how open or closed windows are.
What might be enough one day might not the next because of wind or temperature.


But how do we know we are opening them enough or that we haven’t closed them too much because its cold?

That’s where CO2 monitors can help. In most classrooms we want to aim for levels of CO2
• Ideally bellow 800ppm to 1000ppm.
• We should start to react by increasing the window opening as CO2 climbs above 1000ppm
• And if CO2 is consistently above 1500ppm despite your best efforts then it indicates that the room is under ventilated, and we might need to do something else.


Some important points about CO2 monitors

• CO2 can change quite quickly as people move around and there is air movement in the rooms. What we are interested in are averages over time. Is it mostly bellow 800 or not? Is it hanging around 1300ppm or 1700ppm?
• It is not an alarm, there aren’t rules to say that 1500ppm is bad or not, its just a guide, an indication of how much outside air the room is getting. See it as a tool.
• You want to be sure what you are seeing on a monitor is a fair reflection of the space, so keep it away from windows and doors and direct sunlight.
• And importantly because it measures the air you breath, it needs to be at least 1-2metres away from people. This can be a tall order in classrooms with limited sockets, but really think about where it is. Its no good on your desk with you breathing on it.
• Lastly, every now and then make sure if the room has been left unoccupied over night that you see a low reading on the device of around or bellow 450ppm. You can be sure its correctly calibrated then and giving you a true reading as the space is filled.

Follow manufacturers guidance about how to calibrate the device if required. This should be a rare problem to encounter in classrooms.

In Summary
• If I can keep a classroom below 1000ppm (ideally 800ppm) and be comfortable then the space is working
• If I can’t keep it bellow 1000ppm and be comfortable then the space is not working, can I turn up the heat, improve ventilation or supplement ventilation in the short term with a portable HEPA filter for example
• If I cant keep it bellow 1500ppm regardless of temp or my best efforts of opening windows then the space has a fundamental problem with ventilation that will need to be addressed.

We have created a form to help you record information to assess the classroom.

• The weather on the day (is it cold, mild, windy, what direction, what was the average temp)
• CO2 levels (think average over the last hour)
• Ventilation % (100% is everything open- 0% is everything closed)
• Temperature
• Is the heating on

The information you record now, in winter will provide the data you need to improve the space now and over the summer for next winter.


Author: Simon Jones


> Dowload this article as a PDF

> Download table for C02 monitoring


  1. what is the installation height of the co2 sensor from the floor.

    • Usually eye level

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