This workbook facilitates drawing resistors (and capacitors) for representing a lumped thermal system with a DC electrical analog. The user then applies Excel’s equation solving features to the resulting equations and plots the solution. The simple example illustrated here is steady-state conduction in a Structural Insulated Panel (SIPs) as used in residential construction. The core is expanded polystyrene while the outer layers are oriented strand board (OSB). A similar construction using cement rather than OSB for the outer layers has been proposed for use in earthquake-prone countries such as Afghanistan (Armstrong, D., “Foam Home,” Forbes, June 21, 2004).