Radiant panels are composed of 4 and/or 6 metres modules and different lengths are therefore obtained by connecting the pipes of each modular element by means of welding or pressfitting. To complete this operation without damaging painted plates, pipes are left longer than plates themselves on both sides. When pipe coupling is complete, a joint covering is inserted between the plates, to cover the connection area. Joint coverings have the same profile as main plates and laboratory tests confirm that the thermal output is exactly the same as the active plate of the panel where they are positioned. Joint coverings are easily inserted from below between the plates and fastened with clips, so that installation times are reduced to the minimum level.