Measuring carbon dioxide, or CO2 is the current standard for measuring indoor air quality in a home, school or office. High carbon dioxide levels indoors mean there is not enough fresh air in a building. In addition, high CO2 levels are shown to be correlated with high levels of airborne dust, mold, bacteria and indoor air pollutants.
To analyze carbon dioxide in the air, you can use CO2 indoor air quality monitors. These monitors have small sensors inside that use infrared technology to measure the amount of CO2 in the air. These devices range from $50-$500.
How accurate is a CO2 home tester?
The accuracy of a CO2 tester depends on its type, model, and the conditions it is used in.
Most home carbon dioxide testers are accurate within a range of +/- 50 ppm. For example, if the carbon dioxide level is 400 ppm, the CO2 tester reading can range from 350 to 450 ppm on the display. While factors like temperature, humidity, or airflow can influence a tester's accuracy, in general, the higher the accuracy listed by the manufacturer, the better the device.
So while a CO2 tester is a good way to check indoor air quality its accuracy depends on the device and environment.
CO2 Tester for Home Use and Indoor Air Quality
In order to measure CO2 levels in your home, you will need a carbon dioxide monitor or tester. With a CO2 tester you can easily and affordably measure carbon dioxide levels in your home. These devices come in several different types including handheld, desktop, or wall-mounted units. Some testers may also measure temperature, dew point, humidity, or VOCs (volatile organic compounds).
When picking a CO2 tester for home, think about accuracy, range, and how easy it is to use. Look for a device that is easy to maintain. For example, an NDIR CO2 tester that has an ABC (automatic background calibration) feature will recalibrate itself weekly. This guarantees an accurate reading over many years of use.
But once you know a CO2 level in your home, office or classroom you need to know the normal and above average CO2 levels.
What is an acceptable level of CO2 in a home?
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 help you understand the levels in your home. You can refer to this list when you read your CO2 monitor. ASHRAE suggests keeping indoor levels below 1,000 ppm in schools and 800 ppm in offices for better air quality.
| ~400 ppm | background (normal) outdoor air levels |
| 400 - 1,000 ppm | typical levels found in occupied spaces with good air exchange |
| 1,000 – 2,000 ppm | levels associated with complaints of drowsiness and poor air |
| 2,000 – 5,000 ppm |
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 |
| > 5,000 ppm | Workplace exposure limit (as 8-hour TWA) in most jurisdictions. |
CO2 Levels and your Health
Normal outdoor air has approximately 400 ppm (0.04%) CO2 by volume. Occupied spaces with good air exchange usually have 400 -1,000 ppm. Levels of 1,000-2,000 ppm often associate complaints of drowsiness and poor air quality.
Levels at 2,000 - 5,000 ppm CO2 by volume are often indicators of poor air quality and can be associated with headaches, sleepiness, and stagnant or stuffy air. Many professionals view this level as a core indicator for poor concentration, loss of attention, and reduction of cognitive thinking in confined classroom settings.
We recommend staying between 400 ppm (outdoor CO2 concentration) and 800 ppm for the best quality indoor air.
CO2 Home Tester Experiment
I tested indoor air quality in a home using a TIM10 Desktop IAQ Monitor. CO2Meter has gained recognition for its expertise in indoor air quality and CO2 monitoring.
I gathered data to demonstrate a typical day of CO2 monitoring. This helps to understand the different CO2 levels you might come across on a daily basis.
I used the monitor all day, recorded it as a text file and made a graph in Microsoft Excel. Here's what I learned.
6 a.m.
Woke up and checked the monitor. The CO2 level was 1,380 ppm with two people sleeping in a bedroom and the door closed. While this exceeds the recommended indoor CO2 limits it was not dangerous.
I decided that in the future I'd keep my bedroom door open at night.
7 a.m.
With the bedroom door open, the CO2 level quickly dropped to 650 ppm. In a home or office with people, this CO2 level is normal. If my CO2 levels at home were higher, it would mean I wasn't getting enough fresh air. If the CO2 level was too low, it would indicate too much fresh air and wasted HVAC energy.
It turns out that a sealed house can be just as much of a problem as a drafty one. A sealed house can save you money on energy, but it means you can be trapped inside with high levels of CO2, dust, dander, mold spores, bacteria and all kinds of bad things floating in the air.
8 a.m.
After some time in my home office checking email, it was time to take a morning walk. My new year’s resolution is to actually pay attention to my Apple Watch and get in 10,000 steps a day. The moment I stepped outdoors, the CO2 level dropped to 400 ppm and stayed at that level for my walk.
9 a.m.
I decided to make a quick trip to the local Starbucks for coffee. Since it was about 70 degrees outside, I didn’t use the heater or air conditioning in the car. However, with the windows closed, over 15 minute drive the CO2 level inside the car rose to 1,900 ppm.
The levels dropped when I opened the door and got my coffee. However, they rose again to 2,400 ppm on the way back.
This isn’t surprising. CO2 levels in cars can rise quickly. SenseAir found that even with fresh air ventilation on, a car with 4 adults can reach CO2 levels of 6,000 ppm. Knowing this is important, as drowsiness is attributed to between 10 and 30% of all automobile accidents.
To combat the high level of CO2, I turned on the air conditioning. The effect was immediate, as you can see in the graph. Within 4 blocks, the cabin air quality dipped to 500 ppm.
10 a.m. - 5 p.m.
I spent the remainder of my day alone in my home office with the door open. My CO2 levels at home varied between 750 and 800 ppm. Again, this is perfectly normal. As we breathe, we exhale about 3% CO2 which will raise the CO2 levels in a room over time.
The CO2 level in the house rose when two of us were cooking in the kitchen. It reached its highest point at 1,100 ppm in the family room while we watched TV before going to bed.
Why CO2 Levels at Home Matter
Although my day was normal, I discovered that unintentional exposure to high CO2 levels at home is easy. This is important for everyone, but especially for students and office workers. Harvard researcher Joseph Allen and colleagues found a link between indoor air quality and cognitive performance in a study.
The study discovered that repetitive tasks were not impacted. However, certain cognitive scores were 101% higher in an office that had good ventilation. For me, this means I must monitor CO2 levels in my home office to achieve maximum productivity in the future. Fortunately, simply keeping the door open works for me.
High CO2 levels at home are important because they indicate potential problems with heating and cooling systems, according to experts.
As CO2 levels rise, the quantity of volatile organic compounds (VOCs), odors and micro-organisms in the air rise too. That’s why HVAC engineers use carbon dioxide monitors to regulate airflow in modern office buildings. The same goes for private homes too.
Were my CO2 levels typical for any home?
Perhaps not. The temperature stayed at 70 degrees all day, I shut the windows, and neither the furnace nor the air conditioner turned on. The "tightness" of a house (old vs. new windows, etc.) makes a difference too.
However, the experiment was still interesting, and I'm glad I tried it. Since CO2Meter makes low-cost indoor air quality meters, it is easy for anyone to test their home's indoor air quality.
Best CO2 testers for Indoor Air Quality
It's important to note that while there are many different CO2 testers available, each with its own features and capabilities - the best option for you will depend upon your use case, environment and budget.
10 Tips to Lower CO2 Levels in Your Home
After finding high CO2 levels at home, I wanted to study ways to reduce them.
Here are the top 10 tips I discovered.
- Ensure that your furnace and air conditioning system is working properly. A well-designed system will control the amount of fresh air circulated in your house throughout the day.
- Arrange your home for good airflow by moving furniture away from windows, heating and return air ducts. This will ensure the best airflow.
- Limit open flames. Gas stoves and fireplaces release large amounts of CO2.
- Incorporate plants in your home. Live plants can help purify the air.
- Invest in an air purifier. HEPA filter air cleaners help to control airborne particles when your house is closed up in summer or winter.
- Increase airflow while cooking. If you have a gas stove a hood fan can expel CO2.
- Use natural cleaning agents and non-toxic paint
- Monitor your home's humidity levels. Aim for humidity between 30% and 50% for maximum personal comfort.
- Minimize rug use. Airborne pollutants can easily get trapped in rugs over time.
- Get an indoor CO2 monitor - like one of these.
For more information regarding indoor air quality, carbon dioxide solutions and your home or workspace - contact us today