Open Loop Geothermal Systems

What is a closed loop geothermal system?

A closed loop geothermal system continuously circulates a mixture of water and non-toxic antifreeze through buried or submerged plastic pipes. These underground pipes connect to an indoor heat pump. 

There are 3 primary types of closed loop geothermal systems:

Horizontal Ground Loop: A horizontal ground loop is installed over a wide area of ground and requires enough space to dig trenches hundreds of feet long and 6-10 feet deep.

Vertical Ground Loop: A vertical ground loop is installed in one or more boreholes about 200 to 500 feet deep in the ground. Each hole is 6 to 8 inches in diameter, and if you have more than one, they’re about 20 feet apart.

Pond / Lake Ground Loop: A pond / lake ground loop is installed in a nearby pond or lake with adequate size, depth, and flow. Because this type of ground loop requires a body of water on the property, it’s relatively uncommon. 

What’s the difference between a closed loop and an open loop geothermal system?

Closed loop systems constantly circulate heat-transfer fluid within buried or submerged plastic pipes. The loop is filled just once and requires only a moderate amount of water. The same water is used again and again in a closed loop! That means that the heat-transfer fluid continuously circulates: no fluid can escape, and no outside materials can enter.

In contrast, open loop systems use clean ground water from a nearby well or pond as a heat source or heat sink. After the water transfers its heat with the geothermal heat pump, it’s expelled back into a well, pond, or drainage ditch depending on local codes. Fresh water is continuously pumped into the system and dumped back out. 

Which is better: closed loop or open loop geothermal systems?


Open loop systems are the simplest and often cheapest type of geothermal system to install. Groundwater from an aquifer is piped directly from a well to the home, where it transfers its heat to the geothermal heat pump. After the water leaves the building, it is expelled back into the same aquifer via a second well, called a discharge well, which is located a suitable distance from the first.

That means no trenching, drilling, or burying hundreds of feet of plastic pipe. These costs are unavoidable when installing closed loop geothermal systems. 


Closed loop geothermal systems are practical for small and spacious properties with and without a nearby water source.

Open loop geothermal systems are only an option if there’s a plentiful supply of clean, fresh water on-site. This water source must also meet the geothermal system’s gallons-per-flow requirements, even through seasonal changes. Furthermore, homeowners may only install open loop systems that adhere to local codes and regulations. For fear of environmental contamination or disturbance, some municipalities don’t allow open loop systems at all. 

To learn more about closed loop geothermal systems, check out these frequently asked questions.