[timothyb89]

By far the simplest solution is to just crack a window. Even a modest amount of fresh air exchange is enough to offset most of the CO2 generated by the people inside.

I use a relatively small 10x11ft spare bedroom as my home office. If I close the door and window, it'll quickly climb above 1200ppm after 15-30 minutes (and set off an alarm on my sensor). It'll cross 1500ppm easily if left unchecked. HVAC helps but gets outpaced quickly if my apartment windows are all closed.

That said, keeping doors open, running HVAC normally, and cracking a small window open, even 1-2 inches and on the opposite side of my apartment, is enough to keep CO2 levels around 550ppm while sleeping and 700ppm (in occupied rooms) while awake.