In recent years, heat pump systems have become more energy-efficient and versatile. Much of California is an ideal location for heat pump installation, but in areas where winter temperatures regularly dip below 40°, these systems can be equipped with gas or electric burners that provide supplemental heat in colder weather. Other innovations include the mini-split heat pump, developed for homes without air ducts, and the reverse chiller, a system that generates hot and cold water to circulate in a radiant floor system.