> The next someone gets excited about installing a shiny new heat pump in a place that can get very cold (which includes parts of Arizona!), remember that its c

> The next someone gets excited about installing a shiny new heat pump in a place that can get very cold (which includes parts of Arizona!), remember that its coefficient of performance can get quite low on a cold winter night, Ground loop heat pumps are efficient in nearly any climate short of perma-frost. They do cost a lot and I imagine they aren't exactly cost efficient in Arizona, but the technology means heat pumps are viable even in places where the temperature drops below 0 degrees fahrenheit. The other solution is good insulation so the house doesn't need a ton of heating at night.