Carbon dioxide (CO2) levels can provide incredibly valuable insights into ventilation and air exchange inside your home.
People continuously exhale CO2, so concentrations can rise in bedrooms, home offices, living rooms and other enclosed spaces; especially when doors and windows are closed or fresh-air ventilation is limited.
A home CO2 indoor air quality monitor allows you to track these changes in real time and identify rooms or situations where additional ventilation may be helpful.
While CO2 alone does not represent every aspect of indoor air quality, monitoring it can help you better understand how occupancy, airflow and even everyday activities affect the air inside your home.
What Is a Normal CO2 Level in a Home?
It's important to recognize that outdoor carbon dioxide concentrations are generally around the low-400 ppm range and actual levels vary by location and conditions. Inside a home, CO2 levels typically rise above outdoor concentrations as people breathe, cook, sleep, work and spend time in enclosed rooms. The exact reading considered typical will depend on occupancy, ventilation, room size, outdoor CO2 concentration and other factors.
Rather than treating one CO2 reading as a universal pass-or-fail number, look at CO2 as an indicator of how effectively fresh air is reaching an occupied space.
For example, a bedroom that climbs significantly overnight or a home office that steadily increases during the workday may indicate limited air exchange.
Tracking trends with a CO2 monitor can help homeowners and occupants understand when ventilation changes can make a measurable difference.
CO2 Levels: What's Normal, What's High & How to Measure Them
The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) sets standards for recommended indoor CO2 levels in homes.
Here is a list of CO2 levels per ASHRAE.
This list will not only help you understand the levels in your home but you can refer to this list when you read your CO2 monitor.
ASHRAE suggests keeping indoor levels below 1,000ppm in schools and 800ppm in homes for better air quality.
| 400ppm | background (normal) outdoor air levels |
| 400 - 1,000ppm | typical levels found in occupied spaces with good air exchange |
| 1,000 – 2,000ppm | levels associated with complaints of drowsiness and poor air |
| 2,000 – 5,000ppm |
levels associated with headaches, sleepiness, and stagnant, stale, stuffy air Poor concentration, loss of attention, increased heart rate and slight nausea may also be present |
| > 5,000ppm | Workplace exposure limit (as 8-hour TWA) in most jurisdictions. |
Why Do CO2 Levels Get High Inside a Home?
CO2 levels commonly rise indoors when people produce carbon dioxide faster than fresh outdoor air replaces it.
Bedrooms can experience higher readings overnight when doors and windows are closed, while home offices, living rooms and other frequently occupied spaces can see CO2 increase throughout the day.
The number of occupants, room size, building tightness, ventilation rate and operation of the HVAC system can all influence indoor CO2 concentrations.
Everyday activities can also affect indoor readings as well.
Fuel-burning appliances, cooking, fireplaces and gatherings with multiple people may contribute to changing indoor conditions. A CO2 monitor can help homeowners see these changes as they occur and determine whether actions such as opening a door or window, using appropriate mechanical ventilation or adjusting airflow reduce the measured CO2 concentration.
Where Should You Place a CO2 Monitor at Home?
Place a home CO2 monitor in an occupied area where you want to understand typical breathing-zone conditions, such as a bedroom, home office, living room or other frequently used space.
Follow the monitor manufacturer's placement instructions and avoid locations where the reading could be disproportionately affected by someone's breath, direct outdoor air or other localized conditions.
For example, avoid placing the monitor directly beside an open window, HVAC supply vent, fireplace, or immediately next to someone's face while sleeping or working. If you're trying to understand CO2 throughout your home, consider testing multiple rooms at different times of day.
Bedrooms and home offices are particularly useful places to monitor because people often spend several continuous hours in these spaces.
Real-World Test: How CO2 Levels Change Throughout the Day
Using a Wireless Indoor Air Quality Monitor, I tracked CO2 levels in my home over a typical day.
| Time/Location | CO2 Reading | What Happened |
|---|---|---|
| Bedroom, door closed | 1,380ppm | Two people sleeping |
| Bedroom, door opened | 650ppm | Fresh-air exchange increased |
| Outdoors | 400ppm | Outdoor baseline |
| Car, windows closed | Up to 2,400ppm | CO2 accumulated quickly |
| Home office | 750–800ppm | Door remained open |
| Evening living area | 1,100ppm | Multiple occupants |
Takeaway: CO2 levels can change dramatically based on occupancy and ventilation
How to Choose a CO2 Monitor for Your Home
Look for a CO2 monitor designed for continuous indoor air quality measurement with clear, easy-to-read real-time data.
Depending on your needs, key features may include temperature and humidity monitoring, data logging, smart connectivity, configurable settings and the ability to track changes throughout the day.
CO2Meter's Wireless Indoor Air Quality Monitor measures CO2, temperature and relative humidity and allows users to monitor changing indoor conditions over time. For homeowners, families, remote workers, and other indoor occupants, continuous CO2 measurement can provide useful insight into how ventilation and everyday activities affect the air inside a room.
How to Lower CO2 Levels at Home
The most effective way to reduce elevated indoor CO2 is generally to increase the amount of fresh outdoor air entering the home.
Practical steps may include opening doors or windows when conditions allow, using properly designedventilation, ensuring HVAC and fresh-air systems are operating as intended, using exhaust ventilation appropriately during cooking and avoiding overcrowding in poorly ventilated rooms.
Continue monitoring CO2 after making any changes also, so you can see whether the actions actually improve the measured concentration.
For more information regarding indoor air quality, carbon dioxide solutions and your home or workspace - contact a CO2Meter expert or call us directly at 877-678-4259.
Frequently Asked Questions About CO2 Levels at Home
What is a normal CO2 level at home?
Indoor CO2 varies based on outdoor concentration, occupancy, room size and ventilation. In occupied homes, readings typically rise above outdoor background levels as people exhale CO2.
Why does CO2 increase in my bedroom overnight?
People continuously exhale CO2 while sleeping. In a closed bedroom with limited ventilation, CO2 can accumulate over several hours.
Does opening a window lower CO2?
When outdoor conditions and airflow allow, introducing outdoor air can reduce indoor CO2 concentrations.
Can an air purifier remove CO2?
Typical particle air purifiers, including standard HEPA filtration systems, are not designed to remove carbon dioxide. Ventilation and fresh-air exchange are generally more relevant for reducing accumulated indoor CO2.
Where should I put a CO2 monitor?
Place the monitor in a frequently occupied area according to the manufacturer's instructions and away from locations that could distort the reading, such as directly beside an open window, supply vent, or a person's face.
Are CO2 and carbon monoxide the same thing?
No. Carbon dioxide (CO2) and carbon monoxide (CO) are different gases and require appropriate detection methods.
