Heat pumps used for heating pools transfer heat from the outdoors into the water. Unlike gas heaters that require natural gas or propane, they use heat that is already available and just move it from one place to another, thereby using a cleaner heat via electricity, producing no carbon monoxide.

Heat pump water heaters use electricity to move heat from one place to another instead of generating heat directly. Therefore, they can be two to three times more energy efficient than conventional electric resistance water heaters. To move the heat, heat pumps work like a refrigerator in reverse. Image.