CO2 Levels at Home

by Mark Lemon,

Our new SAN-0001 personal CO2 monitor is so small and easy to use, I decided to measure the co2 levels in my home. I wanted see how much carbon dioxide I'm exposed to every day. Of course, I know carbon dioxide at even moderate levels isn't harmful, but the monitor was free and I was curious. After a full day wearing the monitor, I downloaded the data, exported it to a text file and graphed it in Microsoft Excel. Here's what I learned.

6 a.m. Woke up and checked the monitor. The CO2 level was 1,380ppm with two people sleeping in a bedroom and the door closed. This is well over the National Institute for Occupation Safety and Health (NIOSH) limit of 1,000ppm, and even over the 1,200ppm recommended CO2 level for indoor greenhouses. I opened the bedroom door and made a mental note that if I ever wanted to grow plants indoors, I should keep them in the bedroom!

co2 levels in home over a day

7 a.m. With the bedroom door open, my CO2 levels at home drifted down to aroun 650ppm. While this is above the 400ppm fresh air level, it makes sense that in an occupied home or office the CO2 level should be higher than normal. If my CO2 levels at home were too high, 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.

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 FitBit and get in 10,000 steps a day. The moment I stepped outdoors, the SAN-0001 dropped to 400ppm and stayed at that level for the next hour.

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. Over 15 minutes, the CO2 level inside the car rose to 1,900ppm, dropped while I was in the store, and rose again to 2,400ppm on the trip back.

This isn’t surprising. CO2 levels in cars can rise quickly. In a study conducted by SenseAir, they found that with 4 adults in a car, the CO2 level could reach 6,000ppm even with the fresh air ventilation turned on. This is important to know, as between 10 and 30% of all automobile accidents are attributed to drowsiness.

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 500ppm.

10 a.m. - 5 p.m. The remainder of my day was spent alone in my home office with the door open. My CO2 levels at home varied between 750 and 800ppm.

While not shown on the graph, the CO2 level in the house began to rise on the SAN-0001 with two of us in the kitchen making dinner, and peaked at 1,100ppm in the family room watching TV before bedtime.

Why CO2 levels at home matter

While my day was normal, I learned that it’s easy to be unintentionally exposed to high CO2 levels at home. This is important for everyone, but especially for students and office workers. In a study led by Harvard’s environmental health researcher Joseph Allen in collaboration with colleagues from Harvard, SUNY, and Syracuse University, they observed a direct correlation between indoor air quality and cognitive performance.

According to the study, while repetitive task performance was not impacted, certain cognitive scores were 101% higher in an office environment with a high outdoor air ventilation rate. To me, this means that in order to achieve maximum productivity, I need to keep watch on CO2 levels in my home office in the future. Fortunately, simply keeping the door open works for me.

The other reason CO2 levels at home matter is that carbon dioxide levels are considered by many heating & cooling experts to be the "canary in the mineshaft." 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 like the SAN-0001 to regulate airflow in modern office buildings. The same goes for private homes too.

Were my CO2 levels typical for any home?

Perhaps not. It was 70 degrees all day, so the windows were shut, and neither the furnace or 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 IAQ. 

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