Anecdotal, but: I have found opening windows to be very effective at reducing C02 (as measured with a good sensor) and not very effective at changing the temper

Anecdotal, but: I have found opening windows to be very effective at reducing C02 (as measured with a good sensor) and not very effective at changing the temperature even when it is significantly colder outside than inside. I live in a single family detached house, so I'm not just getting someone elses heat through the walls. My suspicion is that this has to do with the thermal mass of air versus the thermal mass of the rest of the house - bringing in ~10,000 cubic feet of fresh air with a fan doesnt take long and dramatically improves indoor air quality but doesnt change the temperature much.