This study investigated the impact of the plenum load on the cooling capacity of ceiling radiant cooling panel (CRCP) systems. A two-dimensional simulation model using Physibel BISCO was developed to represent a small room (3.8 m (L) × 2.9 m (H)) equipped with CRCPs. To analyze the plenum load impact depending on the CRCP type (top insulation, and open- or closed-type installation), three cases were considered: closed-type with top insulation (Case 1), closed-type without top insulation (Case 2), and open-type without top insulation (Case 3). The simulation results showed that the presence of the plenum load increased the plenum air temperature and caused the CRCP to absorb part of the plenum load, consequently leading to the enhanced cooling capacity of the CRCPs. When the plenum load increased to 10%–20% of the room load, the cooling capacity was enhanced by 7.9% ~ 16.8%, compared to the case without a plenum load. This implied that CRCPs could be undersized when they are designed without considering the plenum load. Furthermore, the cooling capacity showed a greater enhancement in the CRCPs without top insulation (Cases 2 and 3) than in those with top insulation (Case 1). Particularly, a higher cooling capacity was obtained with a higher water temperature when applying CRCPs without top insulation. The results suggested that open-type CRCPs without top insulation would be a good cooling solution for a room with a plenum because they are suitable for removing the plenum load even at relatively high water temperatures.