An air-source heat pump needs some open space to draw air in and push air out. It may not work well in a narrow alleyway, for example, or up against a hedge. You’ll also need to leave space for people to access the heat pump for servicing and maintenance. For these reasons, heat pumps usually sit on the ground at the back of a property, facing the garden. The unit also needs to be in a spot that isn’t prone to a build up of leaves or localised flooding.
Ground-source heat pumps can be inside, because they don’t need airflow. These heat pumps can be large though, so they’re best suited to a basement or utility room. You also need space for the length of underground pipes. If the pipes are laid horizontally, you’ll need around 250 metres squared of land. The pipes need much less area when laid vertically, so this is a good option for properties with small gardens.