What are healthy indoor CO2 levels? (safe levels, health effects and what to do about them)

CO2 (carbon dioxide) is the fifth most common gas and takes up a large part of the atmosphere. Indoor levels can easily become about twice as high as outdoor levels. Since high levels of CO2 are harmful, it is wise to take measures against rising indoor CO2 concentrations.

Healthy CO2 levels are within the 250 – 1000 ppm (parts per million) range. Higher levels of CO2 can lead to serious health effects from complaints of drowsiness to a lack of oxygen in extreme scenarios. Therefore, it is a good idea to continuously measure CO2 levels and make sure ventilation is sufficient.

When I studied Environmental Sciences, I recall that it was very difficult to concentrate during the Earth and Environment lectures. One day, our professor brought an air quality monitor and revealed that CO2 levels increased fivefold during a lecture. No wonder we were falling asleep!

What is CO2 exactly?

Carbon dioxide is a colorless and odorless gas that makes up a tiny part of our atmosphere. About 0.04% to be precise. CO2 is very important for life on earth but has some negative aspects when concentrations become too high. Global warming is one of them, but negative human health effects and sick building syndrome are another.

The word CO2 and a leaf, drawn on a chalkboard
Picture by Gerd Altmann via Pixabay

Sick building syndrome

Sick building syndrome is a term used for the negative health effects attributed to a building. People complain about several health problems and attribute them to being indoors in a building with poor air quality.

The effects include:

  • headache,
  • eye, nose and throat irritation,
  • dry skin,
  • cough,
  • dizziness,
  • nausea,
  • difficulty in concentrating,
  • fatigue

One of the causes of sick building syndrome is a relatively high level of CO2 .

The health effects of high CO2 levels

The following table shows different levels of CO2 and their effects on our health. The levels are given in parts per million (ppm), which is an indication of the number of CO2 particles per 1 million air particles (there are many different air particles, including oxygen (21%), nitrogen (78%), and CO2 (0.04%).

Levels of CO2 (ppm)ValueNegative health effects
250 – 400Normal (background) outdoor valuesNo negative health effects
400 – 1000Typical occupied space with ventilationNo negative health effects
1000 – 2000Exceptionally highComplaints of drowsiness and poor air
2000 – 5000Exceptionally highHeadaches, sleepiness, poor concentration, loss of attention, increased heart rate and slight nausea may occur. Complaints about stagnant, stale, and stuffy air.
5000Maximum 8-hour exposure limitThis indicates conditions where other harmful gases could also be present. Toxicity and oxygen deprivation can occur.
40000Oxygen deprivation levelOxygen deprivation and CO2 toxicity
315 – 415Global rise since 1960Global warming*
(sources 1,2)
*Global warming does not have direct negative health effects since the CO2 levels are still in the normal range. However, CO2 traps heat inside the atmosphere, and a rise in CO2, therefore, means a rise in global temperatures, causing climate change. This causes sea-level rise due to melting ice caps, desertification, extreme weather events, etc.

What can be done about high CO2 levels?

Ventilation is key

The most important and effective measure in controlling indoor CO2 levels is to ensure proper ventilation. Proper ventilation makes sure that there is enough airflow through the room to constantly provide fresh air. Ventilation ensures the removal of high CO2 levels as well as other air pollutants such as fine dust, volatile organic compounds, etc. You can read more about indoor air pollutants and what to do about them in our article.

Additionally, ventilation provides fresh air that contains normal outdoor CO2 levels of about 400 ppm as can be seen in table 1.


Regular airing makes sure you often get a really good flow of fresh air. This is especially important in spaces that are heavily used and the ventilation system is not up for the task. Think of meeting rooms and packed offices where many people are breathing out CO2 and overload the ventilation system.

Do houseplants help remove CO2?

Well, yes, houseplants do take in CO2 and provide oxygen. However, this effect is unfortunately negligible, and you should never rely on plants over ventilation.

A study on houseplants’ ability to remove CO2 in an office showed that to remove 10% of a person’s exhaled CO2, about 15 high-performing CO2-removing plants were required. High-performing plants means they are in:

  • very good health (proper management of plants)
  • very high light conditions (five times higher than in an average office)

Under normal conditions, you will likely need about 100 plants to adequately reduce CO2 levels. And then still only 10% of one person’s exhaled CO2 will be removed.

So if you’re serious about your indoor CO2 levels, make sure to have proper ventilation installed. Consider houseplants for their large amount of other benefits such as adding color and improved happiness and well-being.

If you want to read more about all the ins and outs of plants and indoor air quality you can read my article: Do house plants improve indoor air quality?

Tulips to brighten up your workspace.
Photo by Alisa Anton on Unsplash

Monitoring your air

An air quality monitor is the pefect tool for measuring your indoor CO2 levels. With an air quality monitor you can respond to worsening air quality in time, making you feel safe and prepared.

When looking for an air quality monitor, i recommend considering one that measures more than just CO2. There are many other compounds that influence your indoor air in a negative way.

A Norwegian company called airthings produces excellent air quality monitors. Their devices are easy to operate (just wave your hand in front of the device) and use an app to show their data directly on your phone.

Discount on Airthings monitors

Use this link to the Airthings Wave Plus air quality monitor to get a discount of about 10%!

Their Airthings Wave Plus monitor measures CO2, VOCs, humidity, temperature, air pressure, as well as radon.