I now have almost four years of electricity and natural gas use for my house via our utility companies. We put in a heat pump in May 2022. Previously, we had two window ACs in bedrooms that we ran almost entirely at night (and only some nights) and a bunch of fans. Last summer, with intense heat, you can barely see an increase in usage—particularly when you factor in inflation and a slow climb upwards in rates. (These are all two-month billing periods and average temps.)
This winter, with some bitter cold temps for Seattle last month, it looks like we paid about 5% less with the heat pump than the same period last year. But it's likely we used substantially more therms to heat the house. (Still compiling that data; it's hard to get apples-to-apples.) This chart shows hours used for AC, heat pump heat, and nat-gas heat. (We're still using the nat-gas furnace a bit; need to consider whether turning it off turns into a maintenance problem.)
Based on sheer hours during the coldest parts of December, it's possible we saved something like $75 to $100 in fuel over two months. Hard to pay off a heat pump with those savings, but the overall comfort and the switch to mostly electrical heating and cooling for environmental reasons and efficiency, *and the elimination of all the noise in the summer from fans!* absolutely worth it.
@glennf Electrifying everything is its own reward, but the best deal going is heat pump water heaters which pay for themselves pretty quickly!