Mitsubishi has heat pumps that not only work down to negative 5F they have a COP above 1 that low as well. These same units will stay in primary mode down to negative 13F at which point the COP drops below one and they switch to secondary heating. This means that until negative 13F this heat pump is more efficient than gas or resistive electrics. It’s a function of physics no amount of political BS can.change the second law of thermodynamics heat pumps will always be more efficient than gas which is a first law combustion process ALWAYS. You cannot avoid the loss of energy from the HHV to LHV due to Carnot. Welcome to the 21st century but luddites gonna be luddites. Ground source heat pumps are the most efficient on the planet bar none as the ground world wide is an avg of 55 degrees below the frost line year round.
https://www.mitsubishicomfort.com/articles/keep-warm-this-winter-inverter-technology-for-any-climate
That's until you draw all the heat from it. For adequate heat you either need a large area dug up 10 feet deep or at least two deep wells tapping into groundwater.
I have an electric hybrid hot water heater that uses the conventional electrical elements and a heat pump. Operating costs are considerably cheaper than an electric water heater. I don’t have access to gas.
We are way behind the far east on heat pumps. Those mini split systems are crazy efficient.
“This means that until negative 13F this heat pump is more efficient than gas or resistive electrics.”
Yep, they are more ‘efficient’ than gas...but gas is (or at least was) FAR CHEAPER per kwh (or BTU), so gas still came out ahead of heat pumps, although not by much.
But what about cost? Quick search looks like an air pump is 2-4x the cost of a regular AC unit, and ground pumps are 3-4x the cost of the air pump, assuming you have the land space to even install the loops. Sure, it might be energy-efficient to get them installed, but is it really cost efficient? Saving $100 a month can, for some systems, take a decade or more to be worth it, ignoring opportunity cost. They might make more sense in places like Europe where electricity is expensive and gas is crazy expensive or non-existent, but are they really worth it here in Texas and other places in these US?
But to your -13F efficiency, that’s not what I’m seeing... Most look to be efficient down to maybe 32F, then electric resistance is a cheaper heating option. And a gas furnace is more cost-efficient at much higher temps, especially in Texas where gas is cheap.
“heat pumps will always be more efficient than gas which is a first law combustion process ALWAYS.”
Heat pumps move heat. Burning gas creates heat.
As I understand your post, below a certain temperature the become less efficient than gas or electric heat so not “always”