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How does a CO2 meter work?

How does a CO2 meter work?
Posted on 23-8-2021 by Nienke Vinkenvleugel
How does a CO2 monitor work?
Why measure CO2?
Overview PPM values
How much PPM CO2 is dangerous?
Which CO2 meter is good?
How do you measure the CO2 level?
Why calibrate a CO2 meter?
How many ppm CO2 is normal?
Where to place a CO2 detector?

How does a CO2 monitor work?

CO2, also known as carbon dioxide, is a colourless and odourless gas that we humans breathe out. We only exhale small amounts, but over the course of an entire day, this can steadily increase in your home, at school or in the office. The ratio of CO2 values in the air is expressed in PPM (parts per million). By installing a CO2 monitor, the amount of carbon dioxide in the air can be measured and, based on the result, action can be taken.

Why measure CO2?

It is important that rooms in which several people are present for a long period of time are well ventilated. When CO2 levels are high in certain rooms, this means that the brain is receiving less oxygen than it should. A CO2 level that is too high can lead to headaches, poor concentration, worsening allergies and a faster spread of viruses such as the coronavirus. In short, this creates an unhealthy living environment and then CO2 can be a cause of health problems.

To prevent this, the installation of a CO2 detector is a good solution. This allows the air quality to be measured and an unhealthy living environment to be prevented. But how does a CO2 meter work exactly? A CO2 monitor gives an accurate indication of the amount of carbon dioxide in the air in parts per million. This meter will sound an alarm when there is a dangerously high concentration of CO2 in the room.

Overview PPM values

Below are the values that the device can indicate and what these values mean for you.

  • 450 to 800 PPM The room you are in is well ventilated.
  • 800 to 1200 PPM A poorly ventilated and crowded room. Long-term exposure may impair your level of concentration, among other things. Ventilation is required.
  • 1200 to 2000 PPM Due to the large amount of CO2, the brain will receive less oxygen than desired. Health problems are not inconceivable in this case. Ventilation is necessary.

When the carbon dioxide tester detects an excessively high PPM value in the room, it will indicate that ventilation is required. You can do this in a natural way by opening a window or door, but this is a temporary solution. Ideally, you should ventilate 24/7 with a mechanical ventilation system. The CO2 monitor will tell you whether you need to ventilate more or less.

EnviSense CO2 monitor with data logger - CO2 smart

How much PPM CO2 is dangerous?

All CO2 levels above 1200 PPM should be avoided because they are bad for your well-being and health. With a CO2 level of around 1200 PPM, you will notice that the air is stuffy and unfresh, and you will experience complaints such as:

  • Fatigue, drowsiness and loss of concentration
  • Headaches
  • Worsening of allergies
  • Greater chance of spreading a virus because much of the air in the room has already been inhaled. Not exactly a fresh idea...


Researchers from the State University of New York, among others, even found that even at a CO2 level of 1000 ppm, their test subjects showed a significant reduction in performance. Partly because of this, we recommend to make sure the green light of the CO2 meter is on at all times; the CO2 level then remains below 800 PPM.

Which CO2 meter is good?

There are many different CO2 meters on the market. The meters of a few tens are not very reliable and often give incorrect readings. The CO2 meters on this page have been carefully selected on the basis of quality and user-friendliness. They all have a NDIR sensor and, after many tests and tens of thousands of sales, we can say that they are good. Our choice: the EnviSense CO2 monitor. It measures CO2, humidity and temperature and indicates with red, orange and green whether the air is healthy. A unique feature of this CO2 meter is that it stores all historical values, which can be viewed on the free digital dashboard. Read more about the EnviSense here .

How do you measure the CO2 level?

The CO2 content in the air is measured with a CO2 meter that indicates the content in parts per million (PPM). The best choice is a CO2 meter with an NDIR sensor, also known as an infrared sensor. An NDIR sensor measures how much infrared light of a specific wavelength is absorbed by the surrounding air. Electrochemical sensors also exist, but these can be poisoned, have a shorter lifespan and break down more quickly at high concentrations. This is why all CO2 meters in our range have a NDIR sensor. We also recommend choosing a CO2 meter that can calibrate, such as the EnviSense CO2 meter.

Why calibrate a CO2 sensor?

Whatever CO2 meter you choose, you must be able to rely on the monitor to warn you in time when the CO2 level is too high. When a CO2 meter is in use for a long time, drift (a small change in measurement results from the same device in the same conditions) can occur, regardless of the sensor supplier. The only way to know if your CO2 meter is responding properly is to check it regularly through calibration. The EnviSense CO2 sensor can be manually calibrated and the temperature and humidity can be manually adjusted. We recommend to manually calibrate the CO2 meter at least once a year. How to do this can be found in the FAQ and in the manual of the EnviSense CO2 meter.

How many ppm CO2 is normal?

The CO2 meters with traffic lights indicate very clearly which CO2 levels are good.

  • Green: 400 to 800 ppm is good
  • Orange: 800 to 1200 ppm is medium
  • Red: 1200+ ppm is bad


Outside air is ± 400 ppm, so anything around that value is good and healthy. If the green light is on, the ppm value is normal and the room is ventilated well enough. If the orange light is on, you need to ventilate more, so make sure the green light is always on. If the red light is on, immediate action should be taken by venting and allowing less people in the room.

Where to place a CO2 detector?

It is best to place the CO2 monitor at table height in a place where people do not breathe in directly, because that gives unreliably high readings. Also place the CO2 meter at least 1.5 metres from an open window or door, which would of course be cheating. You can also hang the monitor on the wall. Some CO2 meters have a cable that is shorter than 1.5 meters, you can then use a longer cable or extension lead, or connect the CO2 meter to a computer for instance.
The device is suitable for spaces of up to approximately 100 m2. If the space is larger, you can place multiple CO2 meters or take measurements at different locations in the room.

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