 Heat pump construction that enables carbon dioxide as a refrigerant may have a COP of greater than 2 even down to −20 °C, pushing the break-even figure downward to −30 °C (−22 °F).A ground source heat pump has comparatively less of a change in COP as outdoor temperatures change, because the ground from which they extract heat has a more constant temperature than outdoor air.The design of a heat pump has a considerable impact on its efficiency.