I recently retrofit a new HVAC system and as a result have also gone on a bit of a deep dive on indoor air quality. The big thing I learned is that most homes -- even old "leaky" builds -- have rather poor ventilation, meaning all sorts of compounds build up in the air... CO2, formaldehyde, VOCs, PFAS, etc. Air purifiers work for particulate, but don't really make a dent for chemicals. IIRC, You would need like a 50…
Energy Recovery Ventilators or Heat Recovery Ventilators are absolutely essential (and, I think, part of code in many places!) in this era of tight and sometimes extraordinarily tight (e.g. Passivhaus) home building. When we bought our home, the HRV wasn't working and once I replaced a bunch of parts in it, the difference in the quality of the air was noticeable just in the fact that it smelled fresh like the outdoor…
We have HEPA filters in every room now and portable CO2, PM2.5, VOC monitors, etc for keeping an eye on things. As others have stated, however, this does nothing to address the VOC issue and so I am very keen to take the additional step of installing an Energy Recovery Ventilator or Heat Recovery Ventilator, as you suggest.
If anyone here has Japan or Tokyo-specific information on manufacturers, suitable systems and/or contractors capable of doing the work, I for one would certainly be grateful to hear it!