[stormbrew]

This just seems like unnecessary hair splitting to me. Obviously the efficiency of something is subject to the important inputs and outputs involved.

If someone asks: "how efficient is this heat pump at heating my house?" And you start digressing about how that's the wrong question to ask you'll be giving them an impression opposite reality, which is for most people: it will use less electric energy than heat energy it puts into your house, almost all the time.

[hedora]

There are theoretical upper bounds on the COP though. As heat pumps get better, it may some day make sense to say things like "this heat pump is 95% efficient, so there is no point in replacing it".