To understand the performance of a TEC, one must have an understanding of the total thermal system. A simple resistance model of the thermal circuit can help determine the size of TEC and the operational range from the published curves. For example, if the desire was to control a specific piece of electronics at 55°C and the maximum power of the electronics was known, say 10 W, then a simple thermal circuit diagram could be made using the known or estimated values for thermal resistance for all the parts of the thermal circuit. Shown here in this example, the temperature difference and power input can be estimated for this particular TEC based on the diagram. It may be necessary to iterate the model around the TEC power and delta-T until all the parts of the circuit are consistent. From this model, one can see that the delta-T across the device is 30°C while pumping the 10 W of electronics power. The chart on the left (marked by red stars) shows that the TEC will take 10 W of additional power to pump this wattage across the delta-T. So, the total power rejected to the ambient is 20 W.