The radiator exponent n indicates the change in heat output of a radiator when the actual conditions, in terms of water temperature and room temperature, differ from standard conditions, i.e., the values that were used to define a radiator’s nominal heating capacity.
This exponent is used to calculate the actual heat output for given conditions. The value of the exponent depends on the geometry of the radiator, but in typically general within the range of 1.3 +/- 0.1. The radiator manufacturer supplies the radiator’s exponent n.
The formula to the right can be used with the exponent n to calculate the actual heat output of a radiator for given supply and return temperatures of the water and room temperature.