Filtering the air that enters buildings is essential to ensure a healthy environment. Although outside air is rich in oxygen, it can be contaminated with pollutants that it is important to remove in order to maintain high standards of indoor air quality. The filter box is a specially designed module to enhance the filtration of outside air. Made of galvanised sheet metal, it can house class F7 and F9 filters and is compatible with ducting of different diameters. Being independent of the mechanical ventilation unit, it can be integrated into any air treatment system.