This chapter discusses the heat distribution systems in buildings, including hot-water radiators and radiant panels (floor, wall, ceiling and floor-ceiling), with emphasis on the selection of heating system, evaluation methods of system thermal load (degree-day and bin methods), design of hot water radiator heating networks, adjustability of radiator and radiant floor heating circuits, optimal radiator efficiency, computational numerical models of radiant panels, and PCM incorporation into radiant floor systems. The primary objective of this study is to analyse the energy savings in central heating systems with reduced supply temperatures for different types of radiators, considering the thermal insulation of the distribution pipes. Also, it involves investigating the performance of various low-temperature heating systems and examining the impact of supply temperature on pumping load. Additionally, a comparative analysis of the energy, environmental, and economic performances of floor, wall, ceiling, and floor-ceiling heating systems is performed using numerical simulation with Transient Systems Simulation (TRNSYS) software. Finally, important information is provided for controlling and maintaining the efficiency of indoor heating systems.