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 have serious health effects ranging from minor complaints of drowsiness to oxygen deprivation in extreme scenarios. Therefore, it is wise to monitor CO2 levels and make sure building ventilation is adequate.

I remember during my Environmental Sciences studies that it was particularly hard to concentrate during the Earth and Environment lectures. One day, the teacher brought an air quality monitor and it revealed that the CO2 levels during class increased fivefold. No wonder we were falling asleep!

What is CO2 exactly?

Carbon dioxide is an odorless, colorless 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 covers all the levels of CO2 and their effects on human health. The levels are given in parts per million (ppm), this is an indication of the amount of CO2 particles in the air per 1 million particles in the air (there are many different particles in the air 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 the potential of houseplants to remove CO2 in an office concluded that in order to remove 10% of a persons exhaled CO2, about 15 high performing CO2 removing plants were needed. High performing in this case meant:

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

In normal conditions, however, it is likely that you will need about 100 plants to reduce CO2 levels. And then still only 10% of one persons exhaled CO2 will be removed.

So if you are serious about your CO2 levels, make sure you have proper ventilation installed. Consider plants for their plethora of other benefits such as adding color and improved happiness and well-being.

If you are interested in all the ins and outs about plants and indoor air quality you can read our article: Do house plants improve indoor air quality?

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

Monitoring air quality

An air quality monitor is a great tool to measure your indoor CO2 levels. With an air quality monitor you are always aware of your surroundings and can respond to deteriorating air quality in time. An air quality monitor makes you feel safe and prepared.

If you are looking to purchase and air quality monitor it is wise to consider a device that measures more than just CO2 since there are many other factors influencing indoor air quality.

I found a Norwegian company called airthings, that produces excellent air quality monitors. They are easy to operate (just wave your hand in front of the device) and send their data to an app on your phone.

Discount on Airthings air quality monitor

By using this link to the Airthings Wave Plus air quality monitor you will get a discount of about 10%!

The Airthings Wave Plus air quality monitor not only measures CO2 levels but also VOCs, humidity, temperature, air pressure, and radon.