High CO2 (carbon dioxide) levels in the house? High CO2 levels in the office?
Here's what you need to know: how to measure it and how to mitigate it.
Many individuals are surprised when it comes to the importance of carbon dioxide monitoring. High CO2 levels have been shown to have a direct impact on overall well-being, productivity, and cognitive skills.
Organizations like ASHRAE provide data surrounding the importance of monitoring CO2 levels indoors and the potential long-term effects of exposure on individuals exposed to high levels of CO2.
Why CO2 Levels Rise Indoors even in Healthy Buildings
Many people assume elevated carbon dioxide (CO2) levels indicate a dangerous gas leak, but in most homes, offices, classrooms and commercial buildings, CO2 naturally accumulates simply because people breathe.
Every occupant exhales carbon dioxide continuously and when fresh outdoor air is not introduced quickly enough through mechanical ventilation or natural airflow, indoor CO2 concentrations begin to rise.
Modern buildings are also designed to be significantly more energy efficient than older structures, often featuring tighter building envelopes that reduce unwanted air leakage. While these designs help lower heating and cooling costs, they can also reduce natural ventilation if HVAC systems are not properly designed or maintained.
As occupancy increases, indoor CO2 concentrations may climb above recommended comfort levels, making continuous monitoring an effective way to evaluate ventilation performance.
Understanding why CO2 builds up indoors allows homeowners, facility managers, schools, and businesses to make informed decisions about ventilation, HVAC operation and indoor air quality improvements before occupants begin experiencing symptoms.
What is a CO2 Indoor Air Quality Monitor?
A CO2 indoor air quality monitor is a device that measures the concentration of carbon dioxide in your indoor environment, helping you maintain healthy air quality, improve comfort, and reduce the risk of drowsiness or poor focus due to elevated CO2 levels.
CO2 monitors can also provide real-time insight into air quality, helping homeowners, facility managers, and safety professionals take immediate corrective actions such as increasing ventilation, adjusting HVAC settings, or opening windows.
By continuously measuring and displaying CO2 concentration in parts per million (ppm), these devices act as an early warning system that alerts you before air quality becomes hazardous or productivity declines. When paired with proper ventilation controls, a CO2 indoor air quality monitor can help maintain fresh air exchange and ensure compliance with critical quality standards from ASHRAE, OSHA, and other health organizations.
Why Continuous CO2 Monitoring is Better than Spot Measurements
Indoor air quality constantly changes throughout the day as occupancy, weather conditions, ventilation rates and HVAC operation fluctuate.
A single CO2 measurement only provides a snapshot of conditions at one moment, while continuous monitoring reveals trends that help identify recurring ventilation problems.
Continuous CO2 monitoring also allows building owners and facility managers to:
- Detect ventilation deficiencies before occupant complaints occur
- Optimize HVAC performance and outdoor air ventilation
- Improve employee comfort, student learning, and occupant productivity
- Reduce unnecessary energy consumption by balancing ventilation with occupancy
- Maintain historical air quality data for facility management and building initiatives.
Many modern indoor air quality monitors provide real-time CO2, temperature, and humidity measurements, allowing users to quickly identify changing conditions and take corrective action before indoor air quality deteriorates.
Which Indoor Spaces are most at Risk for Elevated CO2?
Certain indoor environments are more prone to elevated carbon dioxide levels due to limited ventilation, high occupancy, or continuous human activity.
Spaces such as basements, classrooms, offices, laboratories, restaurants, fitness centers, and living spaces often experience a buildup of CO2 as people breathe and air circulation becomes restricted. In these confined areas, CO2 levels can quickly climb above recommended thresholds, leading to fatigue, headaches, poor concentration, and even health complaints often mistaken for seasonal illness or allergies.
For businesses and institutions, installing indoor air quality monitors in critical zones like conference rooms, laboratories, classrooms, and storage areas can also enhance occupant safety, comfort, and operational efficiency. In homes, they offer peace of mind by identifying hidden ventilation issues in basements, nurseries, or bedrooms.
What is the acceptable CO2 levels in buildings?
The acceptable CO2 levels in buildings depend on various factors, including the specific purpose of the building and the local regulations or guidelines in place. However, there are general recommendations and standards that are commonly followed to ensure indoor air quality.
The most widely accepted guideline for CO2 levels in buildings is based on ventilation rates. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) recommends maintaining indoor CO2 levels below 1,000 parts per million (ppm) as a guideline for acceptable indoor air quality in buildings. Download this CO2 levels chart reference for more information.
Here are the CO2 concentration levels commonly used as guidelines:
Good Indoor Air Quality: Normal outdoor air is around 400ppm. Guidelines state that CO2 levels below 800ppm are often considered as a marker for good indoor air quality. Maintaining CO2 levels below this threshold ensures better ventilation and a higher level of comfort for occupants.
Acceptable Levels: The average indoor environment tends to hold CO2 levels around 400ppm - 1,000ppm. These levels ensure adequate ventilation and a reasonably fresh indoor air quality.
Ventilation Standards: Some countries or organizations have specific regulations or standards for CO2 levels in buildings. For example, the LEED certification system for green buildings recommends a maximum CO2 level of 700 ppm above outdoor levels as part of their Indoor Environmental Quality (IEQ) criteria.
To maintain acceptable CO2 levels in buildings, proper ventilation systems and practices are critical. Regular maintenance and monitoring of HVAC systems, ensuring an adequate fresh air supply, and considering the number of occupants and their activities can help manage CO2 levels effectively.
Click the links below to see each organization's safe carbon dioxide levels and exposure limits:
- OSHA: Occupational Safety and Health Association
- ASHRAE: American Society of Heating, Refrigerating and Air-Conditioning Engineers
- NIOSH: National Institute for Occupational Safety and Health
- USGBC: U.S. Green Building Council
- EPA: Environmental Protection Agency
- U.S. Department of Agriculture
Who Should Use an Indoor Air Quality Monitor?
Indoor air quality monitors are valuable in virtually any occupied building where people spend extended periods of time.
While many people associate CO2 monitoring with commercial buildings, these devices provide benefits for homeowners, schools, healthcare facilities and commercial workplaces alike.
Indoor air quality monitoring is especially beneficial for:
- Homes with limited natural ventilation
- Home offices
- Classrooms and educational facilities
- Commercial office buildings
- Conference rooms
- Fitness centers
- Restaurants and hospitality venues
- Healthcare facilities
- Laboratories
- Manufacturing facilities
By continuously measuring indoor CO2 concentrations, organizations can create healthier indoor environments, improve occupant comfort and make informed decisions about ventilation and HVAC performance.
5 ways to improve air quality in your home
- Replace your furnace air filter
- Control the humidity
- Pay attention to what you bring indoors
- Have your furnace inspected
- Use an Indoor Air Quality Monitor
1. Replace Your Furnace Air Filter
Experts recommend that you change air filters in your central air conditioner, furnace, or heat pump every month they are in use. The air filter’s job is not only to keep the air clean from contaminants, but it also keeps dust and debris out of your heating, ventilation, air conditioning system as well as your duct-work.
Dirty air ducts can be a breeding ground for mold spores in the air. It is far more cost-effective to change your filters regularly than to pay for duct cleaning too.
Replacing air filters is easy - remembering to do it is difficult. Here’s a tip: purchase several air filters at a time, and stack them next to your furnace or HVAC equipment. Next, set an alarm on your smartphone calendar to remind you on the first day of every month to change or clean your filters. Don't have a smart phone? Write the date you've changed the filter on the edge of the filter so you'll know the last time you changed it.
Another common question is, which air filter should I use? According to the experts, the higher the minimum efficiency reporting value, or MERV, the better. MERV ratings signify an air filter’s effectiveness at decreasing airborne particles and contaminants which will improve the indoor air quality in your home.
Learn more about MERV ratings here.
2. Control the Humidity
Your home’s relative humidity should be high enough to prevent coughing and nosebleeds, but low enough that you don’t create moisture problems like mold growth.
Indoor relative humidity levels need to take into account the temperature change between summer and winter. In colder climates, wintertime humidity levels should be 30-40% to prevent condensation on windows and other surfaces. In the summer, humidity can be higher, up to 50-60%.
Learn more about the impact of proper humidity levels in your home.
If you do not have a humidifier or dehumidifier connected to your home’s furnace, you should invest in a humidifier to use in the winter and dehumidifier to use in the summer.
3. Pay Attention to What You Bring Indoors
So many indoor air quality problems can be solved by using a bit of common sense.
- Thinking about new paint or carpet? Don’t do it until the weather allows you to open the windows and release the volatile organic gases (VOCs) like formaldehyde they produce.
- Are you ready to replace your bedding? Look at latex foam mattresses and pillows instead of ones made from cotton or natural fibers, and encase them with dust mite proof covers.
- Need a new vacuum cleaner? Purchase one that includes a HEPA air filter instead of a paper bag.
For people with allergies or asthma, indoor air quality is critical to their overall health and comfort. Here are some additional recommendations from the Asthma and Allergy Foundation of America.
4. Check Your Furnace Yearly
You visit the dentist for regular cleanings, you see your primary care doctor for checkups, and you change your car’s oil regularly too. It is all called preventative maintenance. Your HVAC system needs regular maintenance too. It’s the technician’s job to make sure that your system is operating effectively and that it is burning fuel at 100% efficiency so that no carbon monoxide is leaking into your home.
In addition, a clean heating system will save you money on fuel and prolong your furnace’s life too.
5. Use a CO2 Indoor Air Quality Monitor
An indoor air quality monitor that measures CO2 levels can be used as an "early warning system" for poor indoor air quality.
A CO2 Monitor like the Wireless Indoor Air Quality Monitor can be placed in an office, on a school desk, nightstand or in a central area of the home. What makes it so helpful is the ability to see your air quality in "real-time".
Are CO2 levels too high? This means your HVAC system isn’t working properly, and your air is filled with airborne chemicals, pollutants, and microorganisms that spread colds or can inflame allergies.
Simply put, ask your HVAC contractor to have your system "bring in more fresh air."
Too little CO2 means you have too much fresh air and are wasting heating or cooling energy. A quick and simple way to make
sure you’re enjoying the best air quality available is by using an indoor air quality monitor.
Understanding the importance of carbon dioxide levels and poor indoor air quality is the first step to improving an individuals' overall well being and performance in any home, office, or classroom setting.
CO2 Monitoring is Important Indoors
To provide further perspective, the staff at CO2Meter frequently receives e-mails from customers who have implemented CO2 monitors into their indoor space and are surprised by the reading their new CO2 meter has indicated.
They've found that high CO2 levels indoors can have a direct impact on their quality of life. Here are some examples we would like to share:
High CO2 levels indoors in the workplace
V. Jakimov writes, “The moment I powered the TIM10 a high CO2 level alarm sounded. My CO2 was around 2,800 ppm. I was a bit surprised at first but then realized that my small office gets filled quite fast with breath exhaust carbon dioxide (CO2).”
In a paper published in the journal Environmental Health Perspectives, researchers found that people working in buildings with below-average indoor air pollution and carbon dioxide showed better cognitive functioning than workers in offices with typical VOC and CO2 levels.
Fall asleep at home watching movies
Stephen L. writes, “My friends and I have been surprised at how quickly CO2 builds up in a room full of people. In a basement home theater setup I installed, with six people in a 20’x 20’x 8’ room watching a 2 hour movie, the CO2 concentration went from 400ppm to 2,000ppm by the end of the movie.”
Children sick, tired at school
Ken. C., a science teacher writes, “In one classroom of 30 students after lunch reached CO2 levels of 4,825ppm with the door closed...We noticed a rise in asthma sufferers needing their inhalers later in the day when CO2 levels were the highest, typically after lunch.
We also found a direct correlation to nausea, and headache complaints when levels were over 2,000ppm.
Yawning started about 2,500ppm and progressed to some students just laying their heads down around 3,500ppm."
According to the EPA, indoor air quality (IAQ) directly impacts student academic performance and health. For example, the Chester School District in Connecticut saw the number of asthma-related health office visits decrease dramatically – from 463 to 256 – in a single year after improving the air quality in their schools. The Hartford school district saw asthma-related incidents decline from 11,334 to 8,929 in one school year.
Tired while driving
David R. writes, “Our studies found carbon dioxide levels rise from 400 ppm to over 3,000 ppm in 30 minutes in an enclosed automobile with a single passenger.”
In fact, studies show that drowsiness accounts for between 10% and 30% of all automobile accidents and high CO2 levels are known to cause drowsiness. As a result, high-end auto manufacturers now put CO2 sensors in in their car cabins to automatically add fresh air when needed.
Lower concentration in the morning
A study by the military in South Korea attempted to determine the effect of CO2 levels in sleeping barracks on soldiers shooting accuracy. Two platoons of recruits were put in separate barracks: one with the windows and vents open the other with them closed. After a full night sleep, both platoons participated in shooting accuracy tests.
The military was surprised to discover that the soldiers who slept in well-ventilated barracks had statistically improved shooting accuracy. In fact, they were so surprised that they switched the platoons the second night, repeated the tests, and found that the platoon in the well-ventilated barracks performance improved, while the other platoon’s performance suffered.
How can I monitor my CO2 levels?
There are several methods available to monitor CO2 levels indoors. Here are a few commonly used options:
- Portable/Desktop CO2 Monitors: Portable or Desktop CO2 monitors are devices are devices that can be carried around different areas of a building to measure CO2 levels in real-time. These monitors typically display the CO2 concentration in parts per million (ppm) and may have additional features such as data logging capabilities. Portable monitors are convenient for spot-checking CO2 levels in various locations within a building.
- Fixed CO2 Monitors: Fixed CO2 monitors are permanently installed in specific areas of a building, such as offices, classrooms, or HVAC ducts. These sensors continuously monitor CO2 levels and provide ongoing data. Fixed sensors are often connected to a building's automation or control system, enabling real-time monitoring and integration with HVAC systems for ventilation control.
- Building Management Systems (BMS): Many modern buildings have sophisticated Building Management Systems that can monitor various environmental parameters, including CO2 levels. BMS software can integrate data from multiple sensors throughout the building, allowing facility managers to monitor CO2 levels in different zones and make informed decisions about ventilation and air quality management.
It's important to select indoor air quality solutions based on the specific needs and requirements of the building. Factors such as budget, building size, occupancy patterns, and automation capabilities should be considered when choosing the appropriate CO2 monitoring solution. Additionally, regular calibration and maintenance of the monitoring devices are essential to ensure accurate and reliable measurements.
For more information on indoor air quality solutions or to talk with a CO2Meter indoor air quality expert, contact us today.
Frequently Asked Questions About Indoor CO2 Levels
What causes high CO2 levels indoors?
High indoor CO2 levels are typically caused by inadequate ventilation rather than a dangerous source of carbon dioxide. As people breathe, they naturally exhale CO2, which can accumulate in enclosed spaces if fresh outdoor air is not introduced through open windows or properly functioning HVAC systems. Occupancy, room size, and ventilation effectiveness all influence indoor CO2 concentrations.
What are the symptoms of high CO2 levels indoors?
Elevated indoor CO2 levels can contribute to fatigue, headaches, drowsiness, reduced concentration, slower decision-making, and decreased productivity. While these symptoms are often caused by inadequate ventilation rather than CO2 itself, monitoring indoor CO2 provides an effective indicator of when additional fresh air may be needed.
What is a normal CO2 level in a house?
Outdoor air typically contains between 400 and 450ppm of carbon dioxide. In homes, indoor CO2 concentrations below approximately 800ppm generally indicate good ventilation, while levels approaching or exceeding 1,000ppm may suggest that additional fresh air should be introduced. Actual CO2 levels vary depending on occupancy, building design, and HVAC operation.
Is 2,000ppm CO2 dangerous?
A carbon dioxide concentration of 2,000ppm is generally not considered immediately dangerous for healthy individuals, but it often indicates poor ventilation. At this level, many occupants may experience fatigue, headaches, reduced concentration, and discomfort. Persistent elevated CO2 levels should prompt an evaluation of ventilation performance and indoor air quality.
Resources:
https://indoor.lbl.gov/publications/co2-monitoring-demand-controlled
https://www.osti.gov/servlets/purl/902450
https://www.usgbc.org/credits/new-construction/v21/eqc1
https://www.neefusa.org/health/asthma/health-impacts-indoor-air-quality
https://www.epa.gov/sites/default/files/2014-08/documents/sick_building_factsheet.pdf
