HRV F7 filter vs HRV F8 filter
The difference between F7 & F8 filters is 5% at 0.03ppm (parts per million)
F7 85% to 90% efficient at 0.03 ppm
F8 90% to 95% efficient at 0.03 ppm
Fine air born dust that can only be seen in light & smoke is about 1ppm
Even a G4 bag filter will become F8 by the end of its like, this is the mechanical process in these filters.
As they catch more particles the air can only move through smaller holes and the filter becomes finer.
The difference between the F7 & F8 is very minor and completely unnecessary for Home ventilation. The G4 filter is more than adequate for homes.