An air filter unit for removing contaminations from air comprising: - airflow generating means configured to generate and direct at least one airflow (F) from an air inlet to an air outlet ; - filter means disposed between the air inlet and the air outlet and including at least one filter layer for removing contaminations from the airflow (F); - heating means disposed upstream of the filter means and adapted to heat the airflow (F) directed towards the filter means ; - ejection means disposed upstream of the filter means and adapted to inject a vaporized, gaseous or liquid sterilizing agent into the airflow (F) directed towards said filter means ; and - a duct interposed between the air inlet and the filter means and adapted to feed the airflow (F) to the filter means ; wherein said duct comprises at least a volute-like outlet portion for conveying the airflow (F) to the filter means ; 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 (F), 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 , 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 (F) from an air inlet to an air outlet ; - filter means disposed between the air inlet and the air outlet and including at least one filter layer for removing contaminations from the airflow (F); - heating means disposed upstream of the filter means and adapted to heat the airflow (F) directed towards the filter means ; - ejection means disposed upstream of the filter means and adapted to inject a vaporized, gaseous or liquid sterilizing agent into the airflow (F) directed towards said filter means ; and - a duct interposed between the air inlet and the filter means and adapted to feed the airflow (F) to the filter means ; 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 , 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 . <EOS>