Geothermal HVAC systems typically require a well or loop field to be installed in order to operate. The depth of the well or loop field depends on the size of the system and the climate of the area. Generally, the well or loop field should be installed between 50 and 400 feet deep. The deeper the well or loop field is, the more efficient the system will be. Additionally, the deeper the well or loop field is, the more energy it will be able to extract from the ground.