The invention relates to a device for thermally conditioning a fluid for a motor vehicle, comprising: at least one heat module comprising a core and a shell defining a circuit for guiding the fluid that is to be heated or cooled between the core and the shell, a fluid inlet box (209a) and a fluid outlet box, the inlet box (209a) having at least one fluid inlet canal (225a, 225b) communicating with the fluid guiding circuit. According to the invention, the fluid inlet canal (225a, 225b) has at least one substantially curved portion which is configured to generate a swirling movement in the fluid. The invention also relates to a heating and/or air conditioning apparatus comprising such a device.