Since the power design of the heating element is different in different environments, we normally measure it in terms of power per meter ( how much power can be achieved in a heating zone of one meter).
(1) The power per metre of water heating is between 1-3;
(2) The power per metre of oil heating is between 1-2;
(3) The power per metre of air heating is between 1-1.5;
Above this range, the greater the power and the shorter the life.