Personal computer spreadsheet programs are widely recognized for their business applications but are also well suited for performing numerical thermal analysis. Following a description of the basic steps in numerical thermal modeling, the methodology of implementing spreadsheet solutions is presented. Memory requirements, iteration time, and the structure for parametric studies are discussed. Three techniques for deriving the nodal equations used in numerical thermal modeling are given in detail, Included are the finite-difference approach, the energy balance approach, and the thermal resistance approach. The paper concludes with a detailed example showing how to implement a spreadsheet numerical solution for two-dimensional heat flow through a plate. Heat flux, insulated, isothermal, and convecting boundaries are illustrated.