The combination brick vents come in standard brick size and permit high levels of ventilation through walls whilst also protecting from driving rain and large insect ingress. When used with the HD 9600M, they provide entry of air into underfloor voids of suspended floors.
The bricks can be clipped together for 220 x 150mm or 220 x 225mm combinations.
The gas vent grille, code HD 9300G. This vent meets with the aperture grille requirement of BS5440-2:2000, section 4:1:1:2. (Prevents the entry of a 10mm diameter ball, but allows entry of a 5mm diameter ball.)