Earth-to-air heat exchanger is an efficient complement to the space heating and cooling systems. An earth-to-air heat exchanger system consists of a set of subterranean pipes leading outdoor air to a ventilation room and by collecting geothermal energy saves some energy. This article presents testing of an earth-to-air heat exchanger installation in a residential building in Coimbra (Portugal) during 1 year. An analytical model is developed and verified with data from the system monitoring. Many variables affect the outcome of the model and they are included in the parametric study, namely, pipe length and diameter, air velocity, pipe wall material and type of soil. While the difference between outlet and inlet air temperatures is proportional to the pipe length and ground thermal conductivity and inversely proportional to pipe diameter and air velocity, the evaluation is made in terms of a coefficient of performance. For that, the most important factor is the air velocity while material of the pipe does not have a significant effect.