The article doesn’t go into it, but a key advantage they have is that heat pumps move heat, rather then trying to generate it. So they can move a lot more heat into your house than would be generated by running the electricity they use through a resistor. This makes them effectively more than 100% efficient (the exact amount depends on temperature) as compared with burning a fuel or resistive heat.
It gets hard to say because COP varies with climate. But even in SEER ratings, 17-20 are pretty much the norm for modern systems and I have seen as high as 23. That translates to a 4-4.5 COP in an average climate.
But those COPs get higher the more mild your climate – I am somewhere with quite mild winter where we only get a hard freeze once or maybe twice a year, and generally winter low temps are in the 40-50F range.
I believe the theoretical max efficiency for a heat pump is something like 8.8 COP. In a mild climate like mine, where most of the time if your heat is running it’s to heat to ~70ish from an ~50ish outdoor temp, you’re should be getting a lot closer to 7 than you are to 2.
I’m pleasantly surprised. Right, sometimes I forget that most people don’t live in a deep freeze like Saskatchewan.