If using an AC, it is okay to keep the AC running with the window slightly open. This slows down the CO2 buildup while preserving most of the cooling. I would n

If using an AC, it is okay to keep the AC running with the window slightly open. This slows down the CO2 buildup while preserving most of the cooling. I would never go over 770 ppm though. Also, the Energy Saver mode of an AC obviously results in a much worse indoor CO2 level.