Air Quality Part 2: Carbon Dioxide While Sleeping
Using furnace fan ventilation at night drops indoor CO2 levels in my house by 700ppm or more. Supposedly this means better quality sleep.
Does reducing the CO2 level in your house give you a better quality of sleep? It seems like yes.
Now that I have this air quality monitor and my radon problem fixed, I have been moving the monitor systematically over the house to verify that the radon is gone. But the monitor also measures other things, such as Carbon Dioxide / CO2. I noticed that our levels change a lot. Here is a chart of four nights, turning the fan off, on, off, on:
Tracking CO2 levels at night over several weeks I see the following trends:
Summertime, windows open, no people: 450ppm
Summertime, windows open, people sleeping in room: 600 - 650ppm
Windows closed, with furnace fan on (no heat, just air): 900ppm
Doors and windows closed, no ventilation: 1600 to 2100ppm
That’s a big difference!
In this case I’m sleeping with the windows and doors closed - it’s still winter! But whether I measured just one person, two people, or two people plus a dog all sleeping in the same room - the CO2 levels all rose at night when there was no ventilation.
Various sources seem to recommend a healthy CO2 level is 1,000ppm or lower, with “good” indoor readings ranging from 500ppm to 900ppm. Anything over 1,500ppm is rated as “take action to fix”, and levels over 3,000ppm seem “bad”.
So I started to wonder - what is the research? Do CO2 levels affect my quality of sleep? Anecdotally - is usually *feels* like I get a better night’s sleep in the summer if I sleep with a window open. But is there scientific evidence?
Research: Effects of High CO2 While Awake
Several studies note that increased CO2 levels make it harder to stay awake or think:
“At 1,000ppm and 2,500ppm CO2 participants had statistically significant and meaningful reductions in decision-making performance.” —Satish et al. 2012
“Effects on cognitive performance begin at 1000 ppm during short-term exposure.” Azuma, Kagi, Yanagi, Osawa 2018
“Cognitive function scores were 50% lower with CO2 concentrations of 1,400ppm.” —Allen et al. 2016. Article in The Guardian 2019
“A mental task requires a greater effort when the CO2 concentration in the air reaches 3,000ppm.” —Kajtár, Herczeg 2012
“Doubling ventilation rates improved performance by 14%.” —Wargocki, Wyon 2013
For pilots: "Compared to a CO2 concentration of 2,500ppm, the odds of passing a maneuver in the simulator were 1.52 times higher when pilots were exposed to 1,500ppm and 1.69 times higher when exposed to 700ppm." —Allen et al. 2019
Does Lower CO2 Help You Sleep Better?
But how about sleeping? Several studies also seem to show evidence that lower CO2 levels improve both subjective and objective measures for quality of sleep:
Reducing CO2 from 2,400ppm to 900ppm while sleeping:
”Both sleep quality and next-day performance [were] improved by increasing the clean outdoor air supply rate. .. Students spent a greater percentage of their time asleep .. and also tended to perform better on the cognitive tests. They reported that they felt better and more rested.” — ASHRAE - “Indoor Air Quality Tactics To Sleep Better” , Wargocki et al. 2015
“Both subjective and physiological results showed that sleep quality decreased significantly with the increase of CO2 concentration [from] 800ppm to 1900ppm or 3000ppm” —Xu, X, Lian, Z, Shen, J, et al. 2020
“Sleep quality would not be negatively affected when the CO2 concentration was below 750ppm, however, CO2 concentration above 2,600ppm would disrupt sleep duration and negatively affect next-day cognitive performance.” —Sekhar et al. 2020
Those ranges - changing from 900ppm to 1,900ppm or 2,400ppm - sound like the same range I am seeing!
I am not an expert, but this makes me feel like I should keep the ventilation on regularly to try and improve my quality of sleep. It is unfortunate that I just spent several years working to air seal and tighten my house to reduce energy use - and now I want to increase ventilation! I can see why modern building experts suggest you really need proper ventilation for your house.
Unfortunately my house was not built with an ERV, and may be too old to easily retrofit one - not without tearing out many walls and ripping apart the house. For now, I’ll stick with the fan.
..
[Edit, summer 2023]: Add numbers for summertime CO2 levels. Usually 450ppm with no one in the room, 650ppm with people sleeping + breathing.