I've found an in-window fan unit (blowing outward) is very effective at keeping CO2 levels down. Noisy, though. Before that, overnight CO2 levels exceeded 2,60

I've found an in-window fan unit (blowing outward) is very effective at keeping CO2 levels down. Noisy, though. Before that, overnight CO2 levels exceeded 2,600ppm. Now around 700 or so. Can go lower if I crank the fan up. Now I have the new problem of poor thermal regulation. My window is directly above my HVAC duct, so cool air goes straight from my air conditioner through the fan and out the window. I plan to wire up a microcontroller to turn the window fan on and off based on both CO2 levels and A/C activity, but I'm not really happy with the the setup. Too hacky, too much noise, and I need to seal the window screen better to keep bugs out. I've tried just keeping a window open, with no fan, but my CO2 sensor indicated it wasn't super effective. Plus you have to make sure you close the window when it rains otherwise muggy air fills the bedroom.