An analytical and computational model for a solar assisted heat pump heating system with an underground seasonal cylindrical storage tank is developed. The heating system consists of flat plate solar collectors, an Underground cylindrical storage tank. a heat pump and a house to be heated during winter season. Analytical solution of transient field problem outside the storage tank is obtained by the application of complex finite Fourier transform and finite integral transform techniques. Three expressions for the heat pump space heat requirement during the winter season and available solar energy are Coupled with the solution of the transient temperature field problem. The analytical Solution Presented can be utilized to determine the annual variation of water temperature in the cylindrical store, transient earth temperature field surrounding the store and annual periodic performance of the heating system. A computer simulation program is developed to evaluate the annual periodic water and earth and system performance parameters based oil the analytical Solution. Copyright (C) 2003 John Wiley Sons, Ltd.