Abstract: An air temperature control system which is highly energy efficient and virtually maintenance free. The system includes an intake conduit for receiving air at a non-selected temperature, an exit conduit for delivering the air at a controlled temperature to a preselected location, a heat exchanger located below the surface of the ground, and a heat sink preferably of limestone which surrounds the heat exchanger and which adjusts the temperature of the air flowing through the heat exchanger to a controlled temperature. A fan effects the flow of air through the system.