I have real building with hot water radiators. Operating regime is 65/45oC. The manufacturer data provides radiator nominal capacity at standard conditions (Twin=90oC, Twout=70oC, Tair=20oC). When the operating conditions differ from nominal conditions then every baseboard capacity should be recalculated on operating conditions (in my case operating capacity will decrease so larger radiators are installed in order to cover heating load). I made simplification in my model and tried to model them as Baseboard:Convective:Water. When I calculate UA value from manufacturer data and maximum flow rate, and cross-check when the fields are set to autosize, I see that my values for UA are greatly undersized compared to autosize outputs. I tried to model it first with both radiation and convection, but not sure about water mass flow rate (i can calculate it easily) and rated capacity (active length) since flow rate and active length are not "measured/calculated" during rating.