How to calculate the calorific value of the electric heating tube?

Calculation of the calorific value of the electric heating tube:

A voltage regulator can be used to change the heat output by changing the input voltage and current.

The calorific value is proportional to the square of the voltage and proportional to the square of the current.

When the voltage becomes 1/2, the calorific value becomes 1/4

When the current becomes 1/2 of the original, the calorific value also becomes 1/4