"Open a window" is the lay version. The engineering version is in two ASHRAE standards. ASHRAE 62.1 sets ventilation rates for commercial and institutional buildings, offices, schools, hospitals, restaurants. ASHRAE 62.2 sets ventilation rates for residential buildings.
The 62.2 formula (current 2022 edition) is: 7.5 CFM per occupant + 0.03 CFM per square foot of floor area, delivered continuously. A 2,000 ft² home with four occupants needs about 90 CFM of continuous outdoor-air intake. That is roughly equivalent to running a single bathroom exhaust fan around the clock, and that is by design.
In practice, U.S. and Canadian homes meet 62.2 in one of three ways: continuous-running bathroom or kitchen exhaust fan, a balanced HRV/ERV unit (energy-recovery ventilator: the right answer in cold or hot-humid climates), or intentional natural ventilation (cracked windows, trickle vents). The dashboard estimates your effective ventilation rate from the CO2 decay curve when the room is occupied and shows you whether you're meeting 62.2.
Fisk's reviews are unambiguous that increases above 62.2 minimums produce measurable productivity and health benefits, schools and offices benefit from 2× to 3× the minimum rate. The 62.2 minimum is a floor; it is not an optimum.
