Side note: if you can, check your thermostat and see if you can set your thermostat’s “fan mode” to on, instead of auto, for all the schedule settings that apply while you’re in the house. Ecobee allows this (comfort settings -> select presets that apply while you’re in the house -> change heat mode fan and cool mode fan to on). It’s the most effective way I’ve found for lowering CO2 for rooms that don’t have windows or when opening a window is impractical.