Gas cost has varied a bunch over the years I’ve had it, electricity less so. But the furnace has only run a few days per year and only when when it’s been (depending on gas cost) below 10 to -5 degrees Fahrenheit.
My heat pump (trane xv19) kicks ass and if I were doing the hvac upgrade again I’d skip the furnace entirely and let the heat pump work a little harder/longer on the coldest days.
It’s damned near always more cost-efficient to run the heat pump. And my shiny new high efficiency furnace will never, ever pay itself off saving me a few bucks a day the three or four days per year that the math works in its favor.
Electricity can range from 11¢/kWh to 29¢/kWh in California or higher: https://www.energybot.com/electricity-rates/
Natural gas ranges from (converted) ~ 2¢/kWh to 8¢/kWh in Florida: https://www.eia.gov/energyexplained/natural-gas/prices.php (using conversion factors from https://www.nrg.com/resources/energy-tools/energy-conversion..., which I think assumes 1000 ft^3 ~= 1 therm ~= 29.3 kWh)
So your heat pump's COP has to exceed the ratio between natural gas and electricity in your area to make it cost-effective (or you can get solar + battery backup).
Electricity prices can vary quite a bit, too... in Cali, for example, it's gone up from 14¢ to 24¢ over 16 years, which is nearly double the rate of inflation.
What is the make and model of the thermostat you are using?
Is it from the heat pump OEM (Trane?) or a third party?
It’s a rebranded Nexia
* https://www.bayareaservice.com/wp-content/uploads/2020/02/18...
The process to update the costs (which has to be done a few times per year when my utility changes their rates) is not very user friendly - have to get into the technician menus and change scary looking stuff) but it works quite well.
As page where you can enter some numbers:
* https://www.heatpumpswork.com/cop-target
Also, given a US zip code, how often the temperature may drop below 15F / -10C (which is a cut-off for many units):
* https://www.heatpumpswork.com/cold-days
A good HVAC contractor will create a design based on your building and location, and it will cover 99% of average days efficiently for heating and cooling:
* https://www.greenbuildingadvisor.com/article/design-temperat...
* https://www.airequipmentcompany.com/2021/what-does-design-da...
For the remaining 1% it will basically have to run all the time to keep up. (In any given year you may not even get below/above the average outlier 1%.)
OTOH if you’re heating with propane or fuel oil, heat pumps are probably a good alternative.
The best whole house air-source heat pumps had a SEER2 of 18.5, or a COP of just under 5.0. I need a COP of over 5 to just break even in terms of cost efficiency. So a heat pump would actually cost me more on an ongoing basis. And the price for a heat pump installation was $10k more than a furnace/AC.
I just couldn't do it. To pay more up front and then ongoing was just too much. If you showed me even a super long range projection of saving money, I would have been down for it, but it just was not there.
If I can get solar on my house it may make sense, I will cross that bridge in a few years as my roof is almost end of life, but that has its own headaches as I have limited space (brownstone, flat roof), and am in a historic district.
Next go around, as heat pump tech improves and hopefully gets cheaper, it will probably make sense, but for me right now, it just didn't work.
When did you last see a kerosene-powered fridge? It's about 40 years since I last saw one. Hence my 'obsolete technology' label.
Reverse-cycle (heating) heat-pumps rely on fans to extract the heat away from the machine and send warm air into the room. If you have electricity for the fans, you might as well use that electricity to power the heat-pump too.
The fans are a tiny part of the energy used by a heat pump, most of the energy is for running the compressor. Electric heat pumps are more efficient and economical than electric heat, but still generally more expensive than gas heat, and impractical compared to gas if that electricity itself is made from gas in the first place.
If you power a heat pump with gas directly, you are effectively getting over 100% efficiency: you keep all of the heat generated from the gas, plus are 'pumping' heat from outside. It's going to be even more economical than regular gas heat, which is already more economical than anything else.
It makes financial sense in a lot of places to switch to solar plus battery for nearly all energy use. Especially if you can charge your EV directly from solar. Heat pumps at night and in the evening need the batteries though.