Closed Loop Systems
The most common type of geothermal installation is a closed-loop system . The heat exchanger, a loop of piping filled with fluid, is buried underground . The fluid circulates continuously inside the buried pipe, absorbing the heat from the earth during the winter for use inside your home . In warmer months, the fluid takes heat from indoors and transfers it back into the earth . There are two main types of closed-loop systems, horizontal and vertical .
Horizontal Loops
Horizontal loops are installed if adequate land area without hard rock is available. A horizontal loop installation is usually the most economic. They are often used for newly constructed homes but can be installed in retofit projects . The horizontal system uses a number of trenches, a single pipe, multiple pipes in a narrow trench, or multiple pipes in a wider trench. The trenches are normally four feet deep or more, and vary in length depending on the number of pipes to be buried.
Vertical Loops 
If the land available is limited, a vertical loop is installed for the geothermal piping. Vertical installations might also be used where the land is too rocky for trenching, for existing buildings, or for large commercial facilities . To install a vertical loop, a contractor will bore holes into the ground . Long, hairpin-shaped loops of pipe are then inserted . The pipes are connected to headers in a trench leading back to the building . The drilling depth of 150 to 250 feet is average . Drilling boreholes for geothermal loops is much simpler than drilling to find well water . The borehole is generally smaller, which reduces drilling time, and no casing is required .
