The effective implementation of ceiling radiant panel systems requires a precise determination of nominal cooling capacity, a value that can fluctuate considerably due to the interplay of radiative and convective heat exchange within the installed environment. This variability can significantly impact energy consumption, underscoring the critical need for accurate capacity estimation. This study quantifies these variations by establishing a rigorous framework of building boundary conditions, encompassing building fabric, building location, panel location and room size. Using computational simulation and experimental validation within a controlled test cell environment, we systematically assess the relative influence of each building boundary condition on the overall cooling performance of the ceiling radiant panels. Notably, panel location is critical; perimeter installations exhibit markedly higher nominal cooling capacities, increasing from 16.5 W/m2 in the core to 37.5 W/m2 in the perimeter, representing a 43.9 % increase, due to increased indoor surface temperatures resulting from interactions with the building envelope. This highlights the interdependence between nominal cooling capacity and the surrounding environment. Moreover, our analysis reveals a pronounced amplification of the impact of changes in nominal cooling capacity in scenarios characterized by smaller room sizes, lower wall thermal resistance, and buildings situated in regions with higher outdoor air temperatures. These findings emphasize the importance of a nuanced and context-specific approach to the design and implementation of ceiling radiant panels. By integrating the insights, engineers and designers can achieve more precise calculations of the nominal cooling capacity tailored to specific building conditions, ultimately enhancing energy efficiency and occupant comfort.