Abstract: A heat exchange apparatus comprises a plastics outer casing for mounting in the exterior wall of a building such that it extends outwardly of the building wall to define an inlet and an outlet spaced from the wall. A heat exchange block is mounted within the outer casing and defines two paths of air therethrough mutually at right angles and both inclined to the horizontal. The block is formed of a plurality of polypropylene extruded sheets (preferably Coroplast) which comprises two thin sheets supported by a plurality of cells passing along the sheets. The Coroplast sheets are separated by spaces to form elongated air channels. The block is supported within the outer casing on resilient mountings and is arranged such that the air exhausted from the building passes through the elongated channels. A fan drawing air into the building from the exterior through the heat exchange block includes a nozzle for directing the air into the building away from the outlet.