Choose the voltage of the power supply you will use to drive the heater. Next calculate the required resistance R as ΔV2PKnowing the resistivity ρ of the material, choose a combination of wire length and cross-sectional area to make.(lA)=(Rρ) You will have to pay for less material if you make both l and A smaller, but if you go too far the wire will have too little surface area to radiate away the energy; then the resistor will melt.