Abstract: The invention concerns a device of controlling the heat exchange in a crystallizer (26; 126; 226; 326) in which there are cooling channels (48; 148; 348) and one or more temperature sensors (154, 158, 160; 260; 360) which are arranged at the outlet (148b; 248b) of and/or inside the channels measuring the temperature of a cooling fluid to calculate, for example, the temperature difference ?T between different values TOUT at the outlet of different channels to identify non-uniformity in the heat exchange during casting. The outlet temperature sensors can be arranged perimetrally on the crystallizer itself or on a separate cover (272; 372a, 372b) that closes a gap (271) between the crystallizer and a relative ingot mould (227). A relative cover with relative kit and relative continuous casting plant and a method for controlling the heat exchange and a use of the device replacing the crystallizers are also described.