> I use co2 measurements in my home to do just what you're describing here - automate control of a DIY fresh air intake (through a custom built filter box/fan enclosure w/ 5" merv 14 filter).

That’s awesome! A cardboard POC that actually works is a cool project.

> Sadly, it took me a while to figure out that having this window fan in my kitchen on "exhaust" rather than "intake" was creating a negative pressure environment and that was.. not optimal.

Maintaining positive pressure is tricky, one thing that can help is monitoring outdoor air pressure and duct static pressure in the supply duct and controlling fans/dampers to maintain positive pressure by keeping indoor higher than outdoor.