A heat engine enclosing a chamber in housing has two zones maintained at different temperatures. The first zone receives heat energy from an external power source. The second zone is connected to the hot zone by two conduits, such that a fluid (e.g., air, water, or any other gas or liquid) filling the chamber can circulate between the two zones. The expansion of the fluid in the hot zone and the compression of the fluid in the cold zone drive the rotation of the housing to provide a power output. The fluid may be pressurized to enhance efficiency. A cooling fluid provided in a stationary reservoir maintains a preferred operating temperature difference between the hot zone and the cold zone. A heat storage structure containing a fluid with a high heat capacity may be provided as a heat reservoir.