I live in Phoenix, and a heat pump works fine for all my climate control needs, even in summer when I need it cooled by >40 degrees. My brother lives in HI, and he doesn’t have any kind of heater/cooler in his $1M house.
A heat pump is an amazing concept. With the control valve facing one way, you have standard A/C evaporator/condenser and flip it the other way, the evaporator and condenser switch functions, thus turning an A/C into a furnace.
Yup. The Carnot cycle. Pretty cool (pun intended) how nature works.