I have several Airthings Wave connected devices, and I also purchased and installed a Panasonic ERV[0], which I have hooked into my HVAC system. Opening windows several times throughout the day was how I used to control the Co2, but in the winter and summer it became a huge hassle with the temp/humidity changes in the house, but with the ERV running 24/7 I will see an empty room drop to 400 ppm fairly quickly after people leave it (Airthings has an app). Generally rooms with people in them hover around 600-800 ppm with the ERV running. The ventilator will keep the humidity/temp levels pretty consistent because it has this cross capillary core that it runs the air through, but I do need a good few humidifiers running in the winter. The ERV also has the benefit of allowing you to control the air pressure in the house, which is useful for radon, as I was unable to get a good radon pump installed without destroying my downstairs (I live in a raised ranch where the "basement" is the first floor). With the positive pressure in my house + constant ventilation I never see the radon levels generally go above .5.

[0]: https://na.panasonic.com/us/home-and-building-solutions/vent...