Are CO2 Monitors Accurate?

High CO2 levels negatively affect wellbeing and productivity and strongly correlate with disease spread. Thus, particularly during the COVID-19 pandemic, measuring indoor CO2 levels is useful. Popular CO2 monitors include the IQAir AirVisual Pro and Kaiterra Laser Egg + CO2. But how accurate are these CO2 monitors? Smart Air conducted tests to find out.

CO2 Monitor Accuracy Tests

Our tests involved using 2 Laser Egg+ CO2 and 2 AirVisual Pro monitors to measure CO2 levels in our office over 7 days. At the time of writing, the Laser Egg+ CO2 retails at $199 while the AirVisual Pro retails at $269.

Kaiterra Laser Egg+ CO2

Are the AirVisual Pro and Kaiterra Laser Egg CO2 Monitors Accurate?

AirVisual Pro Air Quality Monitor

Are the AirVisual Pro and Kaiterra Laser Egg CO2 Monitors Accurate?

Results: AirVisual Pro and Kaiterra Laser Egg Monitors Measured CO2 Levels Nearly Identical

As seen in the graph below, the CO2 levels measured by the 4 CO2 monitors were nearly identical, bar a few anomalies (which we will go into later).

Are the AirVisual Pro and Kaiterra Laser Egg CO2 Monitors Accurate?

This consistency is a good indication that the four monitors were measuring accurate values of CO2. Because their measurements did not deviate significantly from each other, they were likely tied to the actual CO2 levels in the room.

The average difference in CO2 readings between the Laser Eggs and AirVisual Pro was extremely low, at 5.59 ppm. This is only 0.3% of a CO2 reading of 1600 ppm, which is typical in a crowded room. Thus, the LaserEgg is just as accurate as the AirVisualPro in measuring CO2.

It is unlikely a coincidence that the deviation between the two monitors was so small. This was more likely due to the fact that both are reliable indicators of true CO2 levels.

Monitors Behaved as Expected

Smart Air also altered the environment the monitors were placed in to observe whether they could detect changes in CO2 levels. The alterations were made in the afternoon on day 4, as highlighted by the red box below.

Are the AirVisual Pro and Kaiterra Laser Egg CO2 Monitors Accurate?

Below shows an enlarged view of the CO2 measurements on day 4.

Are the AirVisual Pro and Kaiterra Laser Egg CO2 Monitors Accurate?

12:30: SmartAir staff left the office for food. All monitors reflected a fall in CO2 levels during the lunch break. After the lunch break ended at 13:30, all staff returned to the office and CO2 started to rise again as expected.

15:30: The windows were opened. CO2 in the office was diluted by the fresh air and this was reflected by a decrease in CO2 shown by the monitors.

16:00: CO2 monitors brought outside. As expected, CO2 dropped before rising steadily again after the monitors were brought indoors at 16:30.  

17:30: Smart Air staff exercised in the office. CO2 rose significantly due to the staff exhaling more CO2. Then, CO2 levels remained elevated before the work ended at 18:00 and staff left the office.

Both the LaserEgg and AirVisualPro monitors appropriately recorded the increases and decreases in CO2 as per change in the environment.

                   Data Anomalies Not Due to Monitor Error

Our tests recorded anomalous data at the circled points. Points C and D occurred right at the time Smart Air’s CEO Paddy moved the Laser Eggs from indoors to outdoors and vice-versa. This likely contributed to the significant increase in CO2 as he exhaled.

Are the AirVisual Pro and Kaiterra Laser Egg CO2 Monitors Accurate?

Therefore, the anomalies were likely due to external factors as opposed to instrument error.

Both the AirVisual Pro and Laser Egg also detect dangerous PM2.5 pollution. How accurate are they at detecting PM2.5? Luckily, we have the data. Check out the results in our rankings of the most accurate PM2.5 air quality monitors.

Read More: Ranking of the Best PM2.5 Air Quality Monitors

Calibrating CO2 Monitors

In order to stay accurate, CO2 monitors should be calibrated periodically. The Laser Egg CO2 monitor can be calibrated automatically and manually. The sensor samples CO2 levels for a week and compares the lowest reading to the background level, and adjusts the baseline accordingly. The AirVisual Pro also automatically recalibrates, which can take two to three weeks.

If a CO2 monitor does not have a proper recalibration system, the monitor can quickly become inaccurate at reading CO2 levels.

Update: Smart Air CO2 Monitor

Since publishing this article, Smart Air has launched CO2 monitors. The new 3-in-1 air monitor from Smart Air measures CO2, temperature and relative humidity. Long-lasting with a battery life of up to 30 days, our low-cost monitor gives you the flexibility of choosing the alert thresholds and the frequency of recording.

smart air CO2 monitor

Bottom Line: Are CO2 monitors accurate?

Our tests show that Laser Egg and AirVisual Pro CO2 monitors are likely accurate, as they were highly consistent with each other (deviating only 5.59ppm), and they appropriately recorded changes in CO2 levels. The low deviation between the two monitors is a good indicator that the two CO2 monitors likely closely track true CO2 levels, but it is not confirmation.

Moreover, as anomalous data was not due to instrument error, the monitors have reliable measurements.

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