Abstract: A heater device that is particularly adapted for use in supplying fluids to a living entity, such as a human or an animal. The heater is a transformer and includes a core, a primary winding and a secondary. The core is preferably a pair of E-shaped core sections, each having outer legs and an inner leg, with the outer legs being longer than the inner legs. The core thus forms a receiver opening intermediate the inner legs that slidingly receives a self-contained cartridge enclosing the secondary. The secondary is a planar, tubular conduit shaped in the configuration of an elongated loop and having an inlet for receiving fluid and an outlet for discharging that fluid at an elevated temperature. The extending ends of the outer and inner legs of each core sections face each other and form a receiver opening intermediate the inner legs. The cartridge is insertable and removable from the opening.