Ideally yes, they should have a fresh air intake connected to something like an HRV, but there is still value in dust/smoke/pathogen filtration even if the fres

Ideally yes, they should have a fresh air intake connected to something like an HRV, but there is still value in dust/smoke/pathogen filtration even if the fresh air source for removing CO2 is a different one (i.e an open window). They are definitely better than no air filtration at all.