Don't just assume, measure. I have a newer ~1800sqft home with a good HVAC system and 2 adults and 3 kids in it. We pretty much have to open a door and window

Don't just assume, measure. I have a newer ~1800sqft home with a good HVAC system and 2 adults and 3 kids in it. We pretty much have to open a door and window a couple times a day in the winter to get CO2 levels back down from ~1800-2200. During the milder seasons, we just leave doors and windows open most of day.