Ventilation assembly for directing a forced air flow along a heating/cooling device, such as a radiator or convector, to increase heat exchange thereof with the surrounding air, comprising: - a ventilation unit with: • a housing frame; • one or more fans with controllable rotary speed provided in the housing frame (VL1-VL4); • one or more coupling elements that are arranged for fastening the housing frame on the heating/cooling device; and - a temperature sensor that is arranged for measuring a temperature of the heating/cooling device; - a control unit for controlling the rotary speeds of the fans (VL1-VL4) as a function of a temperature of the heating/cooling device measured by the temperature sensor, wherein the control unit comprises several preset ascending use levels temperature-versus-rotary speed, wherein each preset use level temperature-versus-rotary speed follows its own preset course along which a temperature-dependent rotary speed is set for the fans (VL1-VL4) in such a way that at a higher temperature of the heating/cooling device measured by the temperature sensor, a higher rotary speed is set for the fans (VL1-VL4) according to their own preset course, and wherein operating means are provided for manual selection by a user of one of the preset ascending use levels temperature-versus-rotary speed, characterized in that the several preset ascending use levels temperature-versus-rotary speed are modulation curves (MC1-MC6), wherein each modulation curve (MC1-MC6) follows its own preset course along which a temperature-dependent rotary speed is set for the fans (VL1-VL4) in such a way that at a higher or lower temperature of the heating/cooling device measured by the temperature sensor, a higher or lower rotary speed is set for the fans (VL1-VL4) according to their own preset course. - a ventilation unit with: • a housing frame; • one or more fans with controllable rotary speed provided in the housing frame (VL1-VL4); • one or more coupling elements that are arranged for fastening the housing frame on the heating/cooling device; and • a housing frame; • one or more fans with controllable rotary speed provided in the housing frame (VL1-VL4); • one or more coupling elements that are arranged for fastening the housing frame on the heating/cooling device; and - a temperature sensor that is arranged for measuring a temperature of the heating/cooling device; - a control unit for controlling the rotary speeds of the fans (VL1-VL4) as a function of a temperature of the heating/cooling device measured by the temperature sensor, wherein the control unit comprises several preset ascending use levels temperature-versus-rotary speed, wherein each preset use level temperature-versus-rotary speed follows its own preset course along which a temperature-dependent rotary speed is set for the fans (VL1-VL4) in such a way that at a higher temperature of the heating/cooling device measured by the temperature sensor, a higher rotary speed is set for the fans (VL1-VL4) according to their own preset course, and wherein operating means are provided for manual selection by a user of one of the preset ascending use levels temperature-versus-rotary speed, characterized in that the several preset ascending use levels temperature-versus-rotary speed are modulation curves (MC1-MC6), wherein each modulation curve (MC1-MC6) follows its own preset course along which a temperature-dependent rotary speed is set for the fans (VL1-VL4) in such a way that at a higher or lower temperature of the heating/cooling device measured by the temperature sensor, a higher or lower rotary speed is set for the fans (VL1-VL4) according to their own preset course. wherein the control unit comprises several preset ascending use levels temperature-versus-rotary speed, wherein each preset use level temperature-versus-rotary speed follows its own preset course along which a temperature-dependent rotary speed is set for the fans (VL1-VL4) in such a way that at a higher temperature of the heating/cooling device measured by the temperature sensor, a higher rotary speed is set for the fans (VL1-VL4) according to their own preset course, and wherein operating means are provided for manual selection by a user of one of the preset ascending use levels temperature-versus-rotary speed, the several preset ascending use levels temperature-versus-rotary speed are modulation curves (MC1-MC6), wherein each modulation curve (MC1-MC6) follows its own preset course along which a temperature-dependent rotary speed is set for the fans (VL1-VL4) in such a way that at a higher or lower temperature of the heating/cooling device measured by the temperature sensor, a higher or lower rotary speed is set for the fans (VL1-VL4) according to their own preset course.