> the annual cost to run a heat pump sits well between a natural gas furnace and resistive heating.

Why is that? Maybe I'm missing something fundamentally, but this should be a strict function of COP, $/kWh (elect.) and $/kWh (gas) right? The insolation thing is kind of red herring, because that saves kWh-needed and that goes into both, right?

And yes COP will probably be bad/worst on some days of the year. But on most days even Chicago should get a pretty decent COP from a low-temperature heat pump. Is natural gas just so cheap in Chicago?