A modular heat exchange system for use in central heat exchange installations in buildings, comprising - at least one heat exchange element (100; 120; 140; 160) equipped for exchanging heat between environmental air and a fluid which is conducted through the heat exchange element, said heat exchange element comprising a technical part for conducting said fluid, a wall mount adapted for being fixed to a wall and for holding said technical part and a cover (400; 450) for covering said technical part, the cover having a predetermined first shape with opposite lateral sides (101, 102; 121, 122; 141, 142; 161, 162), and - at least one non-heat-exchange add-on element (500; 520; 540; 560; 580; 600; 620; 640; 660), equipped for adding a given additional functionality to the system, having a predetermined second shape with a complementary lateral side (501, 502; 521, 522; 541, 542; 581, 582; 601; 622; 641, 642) to one of the opposite lateral sides of the cover of the heat exchange element, such that when the heat exchange element and the add-on element are fixed adjacent each other with said complementary sides facing each other, the first shape of the cover of the heat exchange element continues into the second shape of the add-on element, wherein the technical part comprises a front member in a non-heat conductive material, a back member in a heat conductive material and a sealing in between the front and back members for making the technical part substantially fluid-tight; wherein said back member comprises a flat base having one side for contacting said fluid and an opposite side provided with a plurality of upstanding fins spaced at regular distances from each other for exchanging heat with said air; wherein the wall mount is constructed in a non-heat conductive material; and wherein a ventilator is provided at a bottom side of said heat exchange element (100, 120, 140, 160) for drawing air into said heat exchange element. - at least one heat exchange element (100; 120; 140; 160) equipped for exchanging heat between environmental air and a fluid which is conducted through the heat exchange element, said heat exchange element comprising a technical part for conducting said fluid, a wall mount adapted for being fixed to a wall and for holding said technical part and a cover (400; 450) for covering said technical part, the cover having a predetermined first shape with opposite lateral sides (101, 102; 121, 122; 141, 142; 161, 162), and - at least one non-heat-exchange add-on element (500; 520; 540; 560; 580; 600; 620; 640; 660), equipped for adding a given additional functionality to the system, having a predetermined second shape with a complementary lateral side (501, 502; 521, 522; 541, 542; 581, 582; 601; 622; 641, 642) to one of the opposite lateral sides of the cover of the heat exchange element, such that when the heat exchange element and the add-on element are fixed adjacent each other with said complementary sides facing each other, the first shape of the cover of the heat exchange element continues into the second shape of the add-on element, wherein the technical part comprises a front member in a non-heat conductive material, a back member in a heat conductive material and a sealing in between the front and back members for making the technical part substantially fluid-tight;