Filter unit (1) and use of the same, for treating a main through flow (14) of air, said filter unit (1) comprising a main inlet (15) and a main outlet (16) in fluid connection and arranged at a distance from each other, at least one ultraviolet light source (3) adapted for air treatment arranged between the main inlet (15) and the main outlet (16) at least one electrical component (13) for operating the ultraviolet light source (3). The main flow (14), when the filter unit (1) is in use, creates a negative pressure inside the filter unit (1) between the main inlet (15) and the main outlet (16). The filter unit (1) further comprises a compartment (4), separated from the main flow (14), in which compartment (4) the at least one electrical component (13) is arranged. The compartment (4) is provided with a secondary outlet (12) in fluid connection with the main flow (14) and further provided with a secondary inlet (11) in fluid connection to an outside of the filter unit (1) so that a secondary flow (10) from the secondary inlet (11) through said compartment (4) to the secondary outlet (12) is controlled by the negative pressure inside the filter unit (1) when in use.
