Ventilation is usually the best way. Even when there is a temperature differential between the outside and inside, it's more economical to heat up / cool down i

Ventilation is usually the best way. Even when there is a temperature differential between the outside and inside, it's more economical to heat up / cool down in the new air than trying to scrub CO2 [1] If you have an air quality concern, you can start by installing an indoor air quality monitor with a CO2 sensor. [1] https://en.wikipedia.org/wiki/Carbon_dioxide_scrubber https://en.wikipedia.org/wiki/Carbon_dioxide_scrubber