> It's surprising how quickly a room with a closed door and one person can go from ~ambient CO2 levels to 1000ppm+.
Yeah, having seen myself how quickly it happens i've recently been thinking of finding automatic window openers that would respond to CO2 levels reported from either my aranet or on its own.
Maybe just get a heat recovery ventilator.
There is actually one in the house, but I'm not in a situation where I can install one in a specific room or upgrade the in/out flow in that room.