Ventilation Grille A (Art. 9017 1000) Fits over the outside of the air inlet/outlet. Size: 10cm x 22cm (installation size: 8cm x 16cm). Ventilation Grille B Aspen (Art. 9018 1040) Beech (Art. 9018 1038) In wood. 14cm x 22cm. Ventilation Grille C (Art. 9018 1032) For sauna rooms over 25 cu.m. in volume. Vent opening 300 sq.cm. Size: 24.5cm x 25.5cm. Contoured shape. Vent Hatch B Aspen (Art. 9018 1036) Beech (Art. 9018 1034) Fits over the air outlet inside the sauna to regulate air flow. Size: 14cm x 37.5cm. Vent Hatch C (Art. 9018 1030) For sauna rooms over 25 cu.m. in volume. Hatch opens 0 - 300 sq.cm. Size: 24.5cm x 45.5cm.