Filter sequence

Filters sequence for classified cleanrooms

The correct classification of the rooms is achieved if proper filtration is combined with correct air recirculation and also diffused distribution. If one of these items are not satisfied the overall result will be below expectation and validation could be problematic.
Furthermore a correct balance of the overpressure is essential. Consequently, the air escaped by leaks, pass-through and so on, must be replaced with fresh air that must be equal or above the amount required by the personnel working in the clean room.
Here below you can find a table where room classification, air recirculation and filters sequence are related.
For more information refer to manufacturers brochures.

ISO Class Clean room Class F.S. 209 Air Recirculation


Pre Filter Bag Filter 1 Bag Filter 2 HEPA




Ceiling air distribution %
3 1 360-600 G4 F8 H12 U17 90-100
4 10 300-540 G4 F8 H10 U16 90-100
5 100 240-480 G4 F7 F9 U15 20-50
6 1000 40-120 G3 F7 F9 H14 10-20
7 10000 20-40 G3 F6 F8 H14 10-20
8 100000 10-20 G3 F6 F8 H12 5-10