A simplified earth-sheltered building thermal analysis program is described, which makes use of an analytically obtained Fourier-series solution to the governing heat-conduction equation. The Fourier coefficients are obtained numerically by imposing the surface conditions along the boundary. This least squares method requires much less computer storage and run time than other numerical schemes previously used, such as the finite difference and finite element methods. Thus, a method has been developed that could be implemented on a microcomputer and, with further testing, may be used as a tool for design professionals. The simplified thermal analysis program is capable of simulating slab-on-grade, basement, berm, and earth-covered building configurations.