Should You Ventilate While Sleeping? The air-Q Practical Bedroom Test

While sleeping, we release a lot of moisture: partly through breathing, partly through nighttime sweating. Per person, considerable amounts of up to 700 ml of water quickly accumulate, collecting in the air, the mattress, or the bedding. But it's not just absolute humidity (φ) that rises, other air readings do too. Interesting here are carbon dioxide (CO₂) and volatile organic compounds (VOC).

Better to open the window at night? The air-Q self-experiment

We asked ourselves: should you sleep with the window open at night, or is it enough to ventilate well before bed? To answer this question, we ran two different tests with our air quality monitor: on the first day, we only ventilated before sleeping, while on the second day, the windows stayed open the entire night. To keep the data comparable, the starting conditions for our experiment always stayed the same: an approximately 9 m² attic bedroom, including sloped ceilings and two windows, as well as two adult test subjects.

Practical test 1: is ventilating before sleep enough?

On the first test day, we ventilated for an extended period before going to bed, so the starting CO₂ values around 11:30 p.m. were relatively low, under 500 ppm (parts per million). After the windows were closed, though, carbon dioxide content in the room air rose quickly and sharply, reaching its first peak of just under 2,000 ppm after just one hour. After a brief ventilation period of about 15 minutes, the air-Q air quality monitor showed that the values had dropped to about 1,200 ppm. This is still an elevated CO₂ value.

After closing the windows again, carbon dioxide content rose sharply once more, reaching its second peak of just under 2,500 ppm around 3 a.m. The room air was noticeably poor, and relaxed sleep was no longer possible. The windows were therefore opened starting at 3 a.m. and left open for the rest of the night. Due to the two high peak values, the average carbon dioxide exposure was still 1,082 ppm, thus exceeding the Federal Environment Agency's recommended limit value of 1,000 ppm.

Practical test 2: is sleeping with the window open healthier?

On the second test day, we didn't ventilate via open windows before going to bed, but only left the door open. As a result, the air-Q showed higher starting values of 680 ppm compared to the previous day. Shortly before going to bed around midnight, both skylights were opened. Since two adults were now in the room, CO₂ exposure initially rose to about 750 ppm. This peak, however, is significantly lower than the maximum values from the first experiment with the window closed. After this peak, the air-Q air quality monitor detected a clear drop in carbon dioxide values in the room air. By just before 2:30 a.m., values had dropped to about 600 ppm, thus even significantly below the starting values. Between 3 and 5 a.m., the air quality monitor showed fluctuations in CO₂ spikes. Further smaller peaks were recorded here, but their values always stabilized again. From 6 a.m. onward, CO₂ content normalized and settled between 620 and 630 ppm. The average carbon dioxide content was 653 ppm, thus staying clearly below the Federal Environment Agency's recommended limit value.

Conclusion

Our practical test clearly shows that sleeping with the window open is healthier. The charts in our air-Q app show a constant exceeding of the recommended limit values during the first experiment. If the window stays open while sleeping, on the other hand, CO₂ values also fluctuate, but always remain within a normal, unremarkable range. So anyone who has the option to sleep with the window open (without disruptive street noise, for example) should take advantage of it. Besides an adequate supply of fresh air, you can also improve the air quality in your bedroom with suitable green plants. Our practical tests with dragon tree and snake plant show which species are especially well suited for this.