N
nauseous
I can almost guarantee those claimed BTU figures are exaggerated. Like most things all done under ideal settings that bear little to the reality.
Ain't noone got time for dat.You could get a couple of heat meters, plumb them in to the flow and return, make sure that the radiator has the correct flow temperature and delta t, make sure your room is at exactly 20 degrees, and hope it all works.
Compare difference in heat meter readings, convert units as appropriate, and bob's your uncle.