What is a good CO2 level indoors?

What is a good CO2 level indoors?

Imagine a meeting room full of engaged colleagues. The discussions are lively, but after an hour, concentration starts to wane, headaches creep in, and energy levels drop. It’s not necessarily the coffee’s fault – it could be the CO₂ level in the room that has increased. The invisible composition of the air has a major impact on how we feel, think, and perform. But what exactly is a good CO₂ level indoors? And how do we ensure that the air around us supports both health and productivity?

Why is CO2 level important?

CO₂ – or carbon dioxide – is a natural part of the air and a byproduct of our breathing. When we are in closed spaces, the concentration of CO₂ increases rapidly, especially if ventilation is inadequate. A high CO₂ level is not dangerous in itself, but it is a clear sign that the air is not being renewed, and this has consequences.

According to the Danish Working Environment Authority, CO₂ concentration in indoor environments should not exceed 1,000 ppm (parts per million) over a long period of time. When the level exceeds this limit, we start to feel it in our bodies and minds: fatigue, decreased concentration and headaches are common symptoms.

CO₂ levels and their significance:

• Below 1,000 ppm: Good air quality. Ideal for learning, work and well-being.
• 1,000–2,000 ppm: Poor indoor climate. Can lead to discomfort and reduced performance.
• Above 2,000 ppm: Very poor indoor climate. Immediate action is necessary here.

CO2 and human well-being

CO₂ levels are more than just a number – they are a direct indicator of how we feel in our indoor environment. Studies show that high CO₂ levels can negatively affect our cognitive abilities. According to DTU , good ventilation during sleep can improve our mental performance the next day. This applies not only at home, but also in workplaces, schools and daycare centers.

In daycare centers, it is especially important to monitor air quality. A report from Realdania and the Danish Council for Good Indoor Climate documents how poor indoor climate negatively affects children's well-being and learning. The same applies to adults: a poor indoor climate can lead to more sick days and lower productivity.

How to achieve a good CO2 level indoors

The good news is that there are several concrete measures you can take to improve CO₂ levels and thus the indoor climate. Here is an overview of the most effective actions.

1. Frequent and effective ventilation

The classic solution – opening windows – still works. But it’s not just about airing out, it’s about doing it right. According to Bolius , short, thorough ventilation is more effective than leaving the window ajar all day. In winter, it’s especially important to be aware, as heat loss and drafts can be a nuisance. Here, 5–10 minutes of thorough ventilation several times a day is a good solution.

2. Open doors – especially at night

At home, opening doors to, for example, children’s rooms at night can make a big difference. When the door is closed, CO₂ levels rise quickly, especially if the room is small and isolated. By leaving the door open, air can circulate and CO₂ levels can be kept down – a simple but effective solution that many people overlook.

3. Technological support: Indoor climate made visible

In professional environments – schools, offices and institutions – it can be difficult to keep track of air quality manually. Here, technology is a game changer. At ÅBN, we have developed solutions that make it possible to visualize CO₂ levels in real time. Our intuitive sensors and dashboards make it easy to understand and act on the indoor climate – just like checking the weather forecast.

When CO₂ levels become visible, it also becomes easier to change behavior. For example, you can plan breaks, open windows or adjust ventilation when you see that the level is rising. It is an approach that is based on behavior change and data – and one that we at ÅBN have documented the effect of. Read more about our approach to behavior change here .

4. Ventilation systems and maintenance

A well-functioning ventilation system is one of the most effective ways to ensure a good CO₂ level. But this requires that the system is correctly dimensioned, cleaned and maintained. Many buildings have older systems that no longer meet the needs. In this case, a technical assessment and possibly an upgrade may be necessary.

At ÅBN, we collaborate with both public and private stakeholders to analyze and optimize ventilation solutions based on actual measurements and usage patterns. Our Inside solution provides a detailed overview of the development of the indoor climate over time, so decision-makers can make informed choices.

The CO2 level as a strategic parameter

For leaders and facility managers, CO₂ levels are not just a matter of comfort – they are a tool for optimizing the working environment, well-being and operations. A good indoor climate can help reduce sick leave, increase efficiency and attract employees and users. In a time when sustainability and health are on the agenda, it is an investment that makes sense.

Furthermore, measuring and documenting CO₂ levels can be an important part of ESG reporting and green profiling. By integrating technological solutions like those from ÅBN, you don't just get data – you get actionable insights.

FAQ: Frequently asked questions about indoor CO2 levels