Air source heat pumps (ASHPs) transfer heat between your home and the outside air. They work like a fridge in reverse and are therefore sometimes called 'reverse cycle air conditioners'. ASHPs can be used for both heating and cooling. Ground source heat pumps (GSHPs) transfer heat between your home and the ground. They work all year round, providing both heating and cooling, although they are most commonly used for heating. GSHPs need a ground loop, which can be installed in a number of ways: horizontal, vertical or a pond/lake system. Both ASHPs and GSHPs use renewable energy to heat and cool your home more efficiently than traditional fossil fuel systems such as gas boilers. They can also provide hot water. ASHPs are most efficient in relatively milder climates, while GSHPs work best in cooler climates. In the US, ASHPs are more commonly used than GSHPs as the climate is not suitable for GSHPs everywhere.