The use of reverberation rooms for the measurement of a source's radiated power is a well defined and accepted engineering practice. Reverberation room qualification and measurement requirements have been developed over many years and are defined in ISO 3741 / ANSI S12.51. Performing formal radiated power tests in a commercial chamber can often be costly and time consuming. This work investigates the use of a typical "hard-walled room", with many acoustical limitations, for obtaining useful engineering radiated power results. The room's reverberation and diffusivity are evaluated and potential limitations identified as compared to the established specifications. A stiffened aerospace grade sandwich honeycomb panel (satellite equipment panel) is tested in the room and its radiated power / radiation efficiency measured using standard power injection techniques. A second set of power injection measurements are conducted in a commercial reverberation chamber for comparison using the same panel structure. The panel radiated power / radiation efficiency results from the hard-walled room compare favorably with those made in the commercial reverberation chamber in spite of the hard-walled room's high aspect ratio and short reverberation times. Comparisons of critical room parameters such as decay rates, modal densities and modal overlap factors are also presented and their roles in the structure measurements discussed.