A fluid heating system includes a tank assembly having an interior surface bounding a chamber, the tank assembly including a sidewall and a lid. A collapsible bag is removably disposed within the chamber of the tank assembly, the collapsible bag bounding a compartment adapted to hold a fluid. A boiler can be used for pumping heated fluid through the wall of the tank assembly for heating the fluid within the collapsible bag. An impeller is disposed within the compartment of the collapsible bag. An elongated drive shaft is removably coupled with the impeller such that rotation of the drive shaft facilitates rotation of the impeller within the compartment of the collapsible bag. A drive motor assembly is coupled with the drive shaft, the drive motor assembly being adapted to rotate the drive shaft when the lid is in an open or closed position.
