Our radiators are tested in qualified laboratories according to EN-442 regulations which determine the ouput value by fixing the Δт at 50° C. Δт is the difference between the average temperature of the water inside the radiator and the room temperature. The formula is: (((T1 +T2 )/2)-T3 ). Ex.: ((75+65/2)-20)= 50° C. For output values with a different Δт use the following formula: ɸx = ɸΔт50 *(Δтx /50)n . See calculation example of the output at Δт 60° of article 383856: 419*(60/50)1,31404= 533. Output values in kcal/h = watt x 0,85984. Output values in btu = watt x 3,412. LEGEND T1 = supply temperature – T2 = return temperature – T3 = room temperature. ɸx = output to be calculated – ɸΔт50 = output at Δт 50° C (table) – Δтx = Δт value to be calculated – n = exponent ‘‘n’’ (table).