A numerical study was conducted for prediction of the thermal performance of an Earth-to-Air Heat Exchanger (EAHE) for three cities in Mexico. The climatic conditions correspond to a temperate climate (Mexico City), a humid-hot climate (Merida, Yucatan) and an extreme weather (Cd. Juarez, Chihuahua). The effect of thermal insulation at the outlet section of the EAHE is investigated. In Mexico City, the insulation with a thickness of 0.05 m (2 '') is recommended because it improved the performance of the EAHE. In winter, the insulation increased the heating effect up to 2 degrees C with respect to the EAHE without insulation. In summer, thermal insulation provided an improvement on the cooling effect up to 1.3 degrees C. In Merida the results indicate that thermal insulation with a thickness of 0.05 m is also the best option. In winter, this measure improved the heating effect up to 2.6 degrees C with respect to the EAHE without insulation. Particularly, for Cd. Juarez during the summer, the thermal behavior of the EAHE was not improved due to the thermal insulation. Therefore for Mexico and Merida the suggested value of insulation made the EAHE to function properly during all months in summer, since it avoided the undesirable heat gain from the soil at the outlet. In other words, the insulation improved the cooling effect up to 5 degrees C with respect to the EAHE without insulation. (C) 2014 Elsevier B.V. All rights reserved.