Square Charcoal Filter Type B NT AIR Our range hood use a square charcoal filter "Type B" that attaches to the motor to help remove unwanted kitchen smells, this is an optional extra and the chimney section with the pre-cut vent must be used when outside ventilation is not possible. Square Charcoal Filter Type B Compatible with NT AIR Range Hoods, "KA" Line (exception model KA-140) One Square Charcoal Filter Type B for each Range Hood.