Also worth considering in a conduction heating applications is the amount of heat being generated by the element versus the amount of heat being absorbed by the target material. Some losses are unavoidable, but if the part being heated can only absorb 1,000 watts of heat energy per minute at a given temperature differential, and your heating element is creating 2,500 watts of heat per minute, then valuable energy is being wasted. Generating less heat may decrease the temperature differential between heater and part, which can increase the time required to get to a specific temperature, but it can save energy. This see-saw problem of energy efficiency versus time efficiency is a common consideration in the design of a heating process. 

Related: Understanding the Mechanics of Heat Transfer