Special featuresThe filter sets for the DucoBox Energy Premium include the following filters. For supply air (SUP): choice between Coarse 65 % (≈ G4) or ePM1 55 % filter (≈ F7) (Energy Premium only). The ePM1 55 % filter allows less fine particles to pass through and thus has a beneficial effect on air quality (e.g. in case of possible allergic reactions). For extract air (ETA): Coarse 65 % filter (≈ G4)