I am as well. I started out my own journey convinced that we should keep our existing high-efficiency gas furnaces for backup heat, but when we finally did the math, it would have saved us a whopping $3 over the last twelve months vs. using electric resistive backup, and that was using last year's cheaper gas prices...
In the US, if you need backup heating (and you may not, with the heat pumps that are on the. market today), electric resistive heating (heat strips/coils) is indeed more expensive than high-efficiency gas furnaces BTU-for-BTU, but remember that resistive heating runs in parallel with the heat pumps, whereas furnaces have to take over entirely for dual fuel systems. Natural gas might be cheaper than electric resistance alone, but electric resistance plus the heat pump even at diminished capacity can be a very different story.
By the point that heat pumps are going to need supplemental heating, the heat pump is probably operating under a 2.0 CoP (and maybe close to 1.5), so at some point, electric resistant heating (CoP of 1.0) isn’t that much worse than a heat pump in super-cold temps.
(The huge win is the 99% of the year where supplemental heat isn’t needed.)
>The huge win is the 99% of the year where supplemental heat isn’t needed
People advocating for heat pumps seem to be convinced the normal climate, if it isn't warm all year round, is in-between for most of the year. I have never learned why.
Where I live, and it's not Alaska, northern Minnesota or Maine or something like that, there can't be any "win" for six months of the year because there's essentially no need for burning gas anyway. That's separate from the question of exactly how cold a heat pump can be effective.
But from November through April, lows here range from the high 30s to below zero (F). Based on some poking around .gov websites, that is plausibly well into the resistive range.
And again, it doesn't matter how well it works above 40F, because all of the months (6) with lows above 40 require virtually no furnace use.
I've been told that my experience with a heat pump in an apartment where it had to be set to "emergency" (resistive) heat all winter is outdated...but I can't shake the feeling that people are not understanding climates where heating is needed in the first place.
Even at 17°F OAT, a modern heat pump can be over 2.5 CoP and deliver 90% of its rated capacity. [1]
Even on a day with the low in the teens, the high was probably 10-15° higher. Look at the hourly bin data for your location, not just the daily/monthly lows.
The key with a heat pump in a heating dominated climate (on top of insulation which is needed for any energy source) is sizing it right, creating the ducts right, setting the control strategy to not use H2 (emergency heat) too liberally, and not using deep setbacks that will flip you into H2.
Just as you are rightly skeptical of people who can’t comprehend not installing AC, you might be skeptical of drawing too strong and long conclusions from one heat pump install in a rental of unknown quality and where the incentives aren’t aligned to trade-off capital vs operating costs.
> whereas furnaces have to take over entirely for dual fuel systems
Why is that? I see no reason you can't run both, other than a more complex thermostat setup - probably something with an outdoor reset, that kicks in when outside temperatures are too low.
In the US, if you need backup heating (and you may not, with the heat pumps that are on the. market today), electric resistive heating (heat strips/coils) is indeed more expensive than high-efficiency gas furnaces BTU-for-BTU, but remember that resistive heating runs in parallel with the heat pumps, whereas furnaces have to take over entirely for dual fuel systems. Natural gas might be cheaper than electric resistance alone, but electric resistance plus the heat pump even at diminished capacity can be a very different story.