A one-dimensional transient analytical model is proposed to estimate the performance of earth-to-air heat exchangers, installed at different depths, used for building cooling/heating. Two independent space coordinates are considered, one in the longitudinal direction of the buried pipe and the other through the soil, in the vertical direction. With appropriate simplifications, analytical treatment is proposed to predict the temperature fields of the fluid in the pipe and of the soil in the proximity of the buried pipe, taking into account thermal perturbation of the upper free surface and the possible phase change (condensation) in the buried pipes. Moreover, the agreement with some experimental data available in the literature is very satisfactory. (C) 2007 Elsevier Ltd. All rights reserved.