An air filter unit for removing contaminations from air comprising: - airflow generating means configured to generate and direct at least one airflow from an air inlet to an air outlet; - filter means (15, 16) disposed between the air inlet and the air outlet and including at least one filter layer for removing contaminations from the airflow; - heating means disposed upstream of the filter means (15, 16) and adapted to heat the airflow directed towards the filter means (15, 16); - ejection means disposed upstream of the filter means (15, 16) and adapted to inject a vaporized, gaseous or liquid sterilizing agent into the airflow directed towards said filter means (15, 16); and - a duct interposed between the air inlet and the filter means and adapted to feed the airflow to the filter means (15, 16); wherein said duct comprises at least a volute-like outlet portion for conveying the airflow to the filter means (15, 16); and in that the ejection means are arranged in said duct, the ejection means being configured to inject the sterilizing agent transversally to the airflow, characterized in that: a hollow body defines a chamber upstream of that filter means delimited by an upper end wall and a plurality of lateral walls; the hollow body creates an air gap between end wall and filter layer and is configured to receive airflows from the air flow generating means, the volute-like outlet portion of each duct extends within chamber and defines a main outlet opening lying on a plane transversal to the filter layers (15, 16), wherein the volute-like portion is delimited by a curved wall, having an arc-shaped lateral profile and facing one of the lateral walls of hollow body, and by two parallel lateral walls extending on the opposite sides of curved wall, the main outlet opening of each duct is delimited by wall and by head edges of the relative curved wall and lateral walls. - airflow generating means configured to generate and direct at least one airflow from an air inlet to an air outlet; - filter means (15, 16) disposed between the air inlet and the air outlet and including at least one filter layer for removing contaminations from the airflow; - heating means disposed upstream of the filter means (15, 16) and adapted to heat the airflow directed towards the filter means (15, 16); - ejection means disposed upstream of the filter means (15, 16) and adapted to inject a vaporized, gaseous or liquid sterilizing agent into the airflow directed towards said filter means (15, 16); and - a duct interposed between the air inlet and the filter means and adapted to feed the airflow to the filter means (15, 16); a hollow body defines a chamber upstream of that filter means delimited by an upper end wall and a plurality of lateral walls; the hollow body creates an air gap between end wall and filter layer and is configured to receive airflows from the air flow generating means, the volute-like outlet portion of each duct extends within chamber and defines a main outlet opening lying on a plane transversal to the filter layers (15, 16), wherein the volute-like portion is delimited by a curved wall, having an arc-shaped lateral profile and facing one of the lateral walls of hollow body, and by two parallel lateral walls extending on the opposite sides of curved wall, the main outlet opening of each duct is delimited by wall and by head edges of the relative curved wall and lateral walls.