# Material selection of heating element

I am interested in heating coils which are heated using Ohmic/Joule/resistive heating - specifically, how the material for the heating coil is selected.

When I read about heating coil materials - nichrome, carbon fibre etc, the material quality that is mentioned most is electrical resistance (along with a high melting point and stability with changes in temperature). It is my understanding that a high resistance material is typically selected to make heating coils, but how does the thermal conductivity of a material impact the suitability of a material for use as a heating coil?

If two materials had comparable resistance but very different values for thermal conductivity - which material would be the better choice, assuming the goal was a heating coil that heated up quickly using the least amount of electrical power?

1. For maximum power efficiency, you want to match the load impedance (i.e., the heating element resistance) to the source impedance (i.e., the resistance of everything else in the circuit, including the power supply). This is the maximum power transfer theorem. (Volumetric heat generation is $$J^2\rho$$, where $$J$$ is the current density and $$\rho$$ is the resistivity. With a lower load resistance, you're not taking advantage of the circuit current. With a higher load resistance you're dragging down the circuit current.) Choose your material (and its electrical resistivity) and its geometry (cross-sectional area $$A$$ and length $$L$$) accordingly, considering that the linear resistance is $$R=\rho L/A$$.