An open loop system consists of a borehole that has been drilled and lined to abstract water to run though a Heat Exchanger. Unlike a closed loop system that circulates a mixture of anti-freeze and water, the water does not circulate but instead is directed to either a soakaway or discharge point after it has gone through the Heat Exchanger. Typically, due to the volume of water required for the property an abstraction licence and a discharge licence are likely to be required.

Additionally, there is a requirement for filtration and possible chemical treatment of the incoming water to protect the heat exchanger on the Heat Pump. This will require annual maintenance of the system to ensure it continues to function.