Radiant heating systems by floor and/or ceiling panels are examined by the detailed measuring of the inside microclimate in an experimental room in relation with heat transmission through an exposed wall and with ventilation enthalpy flow. The efficiency of the system relates to thermal comfort conditions as well as to energy consumption. The Predicted Percentage of Dissatisfied is computed from every distribution of internal temperatures.What is presented is a rational interpretation of differences observed between experimental and theoretical values of the overall heat transfer coefficient of the exposed wall as of the volumetric heat loss coefficient.The results are compared with those previously obtained with a warm air System. Some information is given about comfort experiments with subjects, performed to confirm the physical diagnostic of the inside micro-climates realized by all the heating systems previously studied.