Experiments were carried out to investigate the performance of a low-temperature radiant floor heating system with different heat storage materials (sand and phase change material) and heating pipes (polyethylene coils and capillary mat) in the floor structure of a test room. Detailed temperatures in both floor structural layers and the air of the room were measured for four different combinations of these thermal mass and heating pipes during charge and discharge operations. The results showed that the floor structure with capillary mat provides more uniform temperature profile in vertical direction of the test room and needs much shorter time (nearly half) to attain the same room temperature than the cases with polyethylene (PE) coils during the charging process. Also, after the heat source was closed, the floor structures using phase change material (PCM) as thermal mass release heat about 2 times longer than the cases using sand. A CFD simulation is also performed which confirms the measured data during the charging and discharging processes. The results indicate the advantages of using PCM - capillary mat combination for low - temperature floor panel typical of solar - hot - water heating system. (C) 2014 Elsevier Ltd. All rights reserved.