An air-exchange device for buildings, designed to be installed between an internal environment and an external environment, comprising, a casing having a substantially flattened parallelepiped shape; a heat exchanger housed inside said casing; and a first fan and a second fan, which have respective intake and delivery sections and are arranged for generating, respectively, a first airflow directed from the inside to the outside and a second airflow directed from the outside to the inside, where the first and second airflows are in a relationship of mutual heat exchange in said heat exchanger.