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As someone who switched to a heat pump recently, you should know "your mileage may vary." Don't confuse physical efficiency for cost efficiency. In many places,

As someone who switched to a heat pump recently, you should know "your mileage may vary." Don't confuse physical efficiency for cost efficiency. In many places, natural gas is still more cost efficient, even if it isn't as efficient in terms of physics.

sgerenser 3y ago
Natural gas is dirt cheap in most of the U.S., so it does make it hard for heat pumps to compete, especially if electricity is expensive. Just checked my most recent gas bill and I only paid $1.09/therm (plus 7% sales tax and $10 fixed fee). OTOH if you’re heating with propane or fuel oil, heat pumps are probably a good alternative.
- grumpyinfosec 3y ago
  Thats kind of high. I only pay $0.78 a therm here in Wisconsin. 1 therm is around 30kwh so im paying like 2.5c a kwh vs 17c for electricity. So unless I can get a CoP of 700% from a air source heatpump im literally lighting money on fire. That really is the main issue, as much as I care about emissions I don't care enough to spend money on a heat pump to then spend more money on utilities. And the calculus gets worse and worse when your poorer.
  - sgerenser 3y ago
    Looks like Wisconsin has lower than average natgas prices vs. rest of U.S.: https://www.eia.gov/dnav/ng/ng_pri_sum_a_EPG0_PRS_DMcf_m.htm https://www.eia.gov/dnav/ng/ng_pri_sum_a_EPG0_PRS_DMcf_m.htm
    - grumpyinfosec 3y ago
      seems pretty comparable to the other colder parts of the country. (besides the east coast) The warmer parts of the US i'd imagine are less sensitive to residential gas prices.
- kevstev 3y ago
  Last year I had to replace my HVAC. I was set on getting a heat pump, being a huge fan of efficiency. I was averaging a $1.05/therm delivered for gas, and about 17.5 cents/kwh for electricity delivered. A therm is about 29 kwh, so I pay the equivalent of $5.07/therm in electricity. 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.
electric_mayhem 3y ago
As someone who switched four years ago to a heat pump plus conventional furnace, I can state from experience that my thermostat takes electricity cost per kWh and gas cost per therm (other units are available, these are just the ones that match my utility bills) and efficiency of both the heat pump and furnace and runs whichever is cheaper. 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.
- solardev 3y ago
  It really depends on your area's natural gas vs electricity prices, which can vary wildly. Electricity can range from 11¢/kWh to 29¢/kWh in California or higher: https://www.energybot.com/electricity-rates/ 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 https://www.eia.gov/energyexplained/natural-gas/prices.php (using conversion factors from https://www.nrg.com/resources/energy-tools/energy-conversion-calculator.html 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.
- throw0101b 3y ago
  > As someone who switched four years ago to a heat pump plus conventional furnace, I can state from experience that my thermostat takes electricity cost per kWh and gas cost per therm […] What is the make and model of the thermostat you are using? Is it from the heat pump OEM (Trane?) or a third party?
epistasis 3y ago
Especially if you get your electricity from PG&E, who charges ridiculously high transmission and distribution fees. 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.
data_ders 3y ago
For how long is gas likely to be cheaper? It’s generally more scarce right? Does anyone have predictions on US price over the next few decades?
- epistasis 3y ago
  As gas use declines, prices are likely to stay low. So probably a long time.
- sgerenser 3y ago
  Fracking has made natural gas extremely cheap in the U.S over the past several years. Apparently, right now its at the lowest inflation-adjusted price since 1990 per the WSJ: https://archive.is/8wEi7 https://archive.is/8wEi7
throw0101b 3y ago
> In many places, natural gas is still more cost efficient, even if it isn't as efficient in terms of physics. As page where you can enter some numbers: * https://www.heatpumpswork.com/cop-target 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 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-temperature-vs-degree-days https://www.greenbuildingadvisor.com/article/design-temperat... * https://www.airequipmentcompany.com/2021/what-does-design-day-really-mean/ 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%.)
_yb2s 3y ago
Gas powered heat pumps also exist, using the same principle as gas powered refrigerators… from what I’ve heard they are already used in some countries but not on in the USA.
- simonblack 3y ago
  They are very likely denigrated as 'obsolete technology', but like all technology there are use-cases where a particular technology works best.
  - _yb2s 3y ago
    Why they would be obsolete if more efficient than regular natural gas heat, which is by far the currently most widely used home heating technology?
    - simonblack 3y ago
      :) 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.
      - _yb2s 3y ago
        modern RVs still widely use propane powered absorption refrigeration, although that is starting to move over to solar and battery arrays. 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.

sgerenser 3y ago

Natural gas is dirt cheap in most of the U.S., so it does make it hard for heat pumps to compete, especially if electricity is expensive. Just checked my most recent gas bill and I only paid $1.09/therm (plus 7% sales tax and $10 fixed fee). OTOH if you’re heating with propane or fuel oil, heat pumps are probably a good alternative.

grumpyinfosec 3y ago
Thats kind of high. I only pay $0.78 a therm here in Wisconsin. 1 therm is around 30kwh so im paying like 2.5c a kwh vs 17c for electricity. So unless I can get a CoP of 700% from a air source heatpump im literally lighting money on fire. That really is the main issue, as much as I care about emissions I don't care enough to spend money on a heat pump to then spend more money on utilities. And the calculus gets worse and worse when your poorer.
- sgerenser 3y ago
  Looks like Wisconsin has lower than average natgas prices vs. rest of U.S.: https://www.eia.gov/dnav/ng/ng_pri_sum_a_EPG0_PRS_DMcf_m.htm https://www.eia.gov/dnav/ng/ng_pri_sum_a_EPG0_PRS_DMcf_m.htm
  - grumpyinfosec 3y ago
    seems pretty comparable to the other colder parts of the country. (besides the east coast) The warmer parts of the US i'd imagine are less sensitive to residential gas prices.
kevstev 3y ago
Last year I had to replace my HVAC. I was set on getting a heat pump, being a huge fan of efficiency. I was averaging a $1.05/therm delivered for gas, and about 17.5 cents/kwh for electricity delivered. A therm is about 29 kwh, so I pay the equivalent of $5.07/therm in electricity. 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.

electric_mayhem 3y ago

As someone who switched four years ago to a heat pump plus conventional furnace, I can state from experience that my thermostat takes electricity cost per kWh and gas cost per therm (other units are available, these are just the ones that match my utility bills) and efficiency of both the heat pump and furnace and runs whichever is cheaper. 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.

solardev 3y ago
It really depends on your area's natural gas vs electricity prices, which can vary wildly. Electricity can range from 11¢/kWh to 29¢/kWh in California or higher: https://www.energybot.com/electricity-rates/ 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 https://www.eia.gov/energyexplained/natural-gas/prices.php (using conversion factors from https://www.nrg.com/resources/energy-tools/energy-conversion-calculator.html 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.
throw0101b 3y ago
> As someone who switched four years ago to a heat pump plus conventional furnace, I can state from experience that my thermostat takes electricity cost per kWh and gas cost per therm […] What is the make and model of the thermostat you are using? Is it from the heat pump OEM (Trane?) or a third party?

epistasis 3y ago

Especially if you get your electricity from PG&E, who charges ridiculously high transmission and distribution fees. 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.

data_ders 3y ago

For how long is gas likely to be cheaper? It’s generally more scarce right? Does anyone have predictions on US price over the next few decades?

epistasis 3y ago
As gas use declines, prices are likely to stay low. So probably a long time.
sgerenser 3y ago
Fracking has made natural gas extremely cheap in the U.S over the past several years. Apparently, right now its at the lowest inflation-adjusted price since 1990 per the WSJ: https://archive.is/8wEi7 https://archive.is/8wEi7

throw0101b 3y ago

> In many places, natural gas is still more cost efficient, even if it isn't as efficient in terms of physics. As page where you can enter some numbers: * https://www.heatpumpswork.com/cop-target 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 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-temperature-vs-degree-days https://www.greenbuildingadvisor.com/article/design-temperat... * https://www.airequipmentcompany.com/2021/what-does-design-day-really-mean/ 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%.)

_yb2s 3y ago

Gas powered heat pumps also exist, using the same principle as gas powered refrigerators… from what I’ve heard they are already used in some countries but not on in the USA.

simonblack 3y ago
They are very likely denigrated as 'obsolete technology', but like all technology there are use-cases where a particular technology works best.
- _yb2s 3y ago
  Why they would be obsolete if more efficient than regular natural gas heat, which is by far the currently most widely used home heating technology?
  - simonblack 3y ago
    :) 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.
    - _yb2s 3y ago
      modern RVs still widely use propane powered absorption refrigeration, although that is starting to move over to solar and battery arrays. 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.