7 ms·

Isn't the primary issue not the cost of installation, but rather the cost of the fuel? Natural gas in most of the US is far cheaper than electricity, and even i

Isn't the primary issue not the cost of installation, but rather the cost of the fuel? Natural gas in most of the US is far cheaper than electricity, and even if heat pumps are theoretically more efficient than natural gas (energy in:heat out), if the fuel is two or three times cheaper none of that matters.

onlyrealcuzzo 4y ago
In most places in the US, in normal working conditions, Heat Pumps are 30%+ cheaper than a gas furnace to run. However, in some really cold places like Chicago, Minneapolis, etc - the days where current heat pumps are inefficient might be enough to make it cheaper to always run gas. OP is proposing to have both systems and only run the gas furnace on extreme days - which would lead to a ~30% reduction in running costs. I suspect the CapEx of having two heaters wouldn't make sense, though. It'd be better to just have a hear pump that can run efficiently at colder temps.
- Scoundreller 4y ago
  I think it’s the opex of 2 grid connections that messes with the numbers. Depends on how your utility charges, but I feel like many/most sell you the gas roughly “at cost” and then some fixed monthly delivery/connection charge that covers their regulated rate of return on their network equity. Oil or propane supplemental heat might be cheaper than Natgas supplemental heat. My money is on wood pellet stoves for supp heat for those that don’t require full automation. Or maybe even dirty coal…
- BobbyJo 4y ago
  Also, the capex of gas delivery. Not needing infra to deliver gas to each and every house would likely be a pretty big win.
  - bombcar 4y ago
    For new construction sure - for existing it’s already there and apparently needs little maintenance.
- mrep 4y ago
  You generally have an air conditioner though as well as a furnace and you can get those that can also work as a heat pump. Mine supposedly works as both but they only set it up for cooling and my gas furnace does all the heating :(
- deleted 4y ago
  [deleted]
Scoundreller 4y ago
Maybe the gas is cheap, but the monthly and up-front connection costs mess with the economics. And that cost will only go up as people cut the gas cord. Depends on how your utility bills out it’s infrastructure: some charge minimal monthly connection fees, others a lot. I honestly wouldn’t want to own a residential-focussed gas distribution company unless someone revolutionizes stirling engines or micro cogen systems and people start cutting their electric cord.
- lizknope 4y ago
  I live in a pretty standard suburban subdivision in the US. All the houses are 25 years old. I have about 60 coworkers in very similar situations. I think everyone of us has natural gas that was installed when the original company built all the homes in the subdivision over the course of a year. Stuff gets a lot cheaper when everything is put into the ground at the same time. My monthly gas connection fee is $10 so that in the summer my bill is around $19 which is $9 for the water heater and $10 for the connection fee.
kube-system 4y ago
The thing with heat pumps is that they can be as much as 300% efficient (effectively) or more. This is because they can get "free" heat from the environment. So even if per unit of energy gas is way cheaper, heat pumps can still come out ahead.
- Epa095 4y ago
  Modern heat pumps can be up to 500% efficient (using 1kWh of energy gives 5 kWh of heat) at optimal temperature.
  - kube-system 4y ago
    Yes, I went with "300 or more" because that's a more typical number for a run-of-the-mill unit.
    - a9h74j 4y ago
      And even the low-temperature-capable heat pumps reduce toward 100% at the low temperature end, IIRC.
      - mikeyouse 4y ago
        Yep, here's a spec sheet for a unit I'm looking at as a drop-in ducted replacement for my existing system -- it has all of the models listed, but I'm looking at the 4-ton unit (12k btu per ton, so 4-ton = 48k BTU, hence the MDU18048): https://mrcool.com/wp-content/dox_repo/mc-uni-perf-ss-en-01.pdf https://mrcool.com/wp-content/dox_repo/mc-uni-perf-ss-en-01.... It takes 7kw at 17ºF to provide 48k BTU. There are 0.293W/hr per BTU so 7,000W = 25k BTU "in" and 48k BTU "out" or a COP of 1.9. At -15ºF, it's using 5.9KW but can only produce 28,500. So a COP of ~1.4. Still better than electric resistive heating but not by much. At 40ºF, the COP is more like 3.3 which is in line with the very efficient numbers. Fortunately my 99% design temp is ~8ºF and my area only sees 20hrs below zero per year, so this will work just fine for me.
- anikom15 4y ago
Epa095 4y ago
Unless gas is subsidised I don't really understand how gas can be cheaper. A modern heat pump can give 3-5 kWh of heat using 1 kWh of electricity. And a modern gas generator is roughly 50% effecient at creating electricity (according to the Internet). So by using electric and a heat pump you should be able to get 1.5-2.5 times more heat from the same gas by making electricity of it first compared to burning it directly.
- njarboe 4y ago
  At least in the US, electricity rates and natural gas prices are highly regulated for retail customers. Thus the wholesale price of gas does not generally correlate to the retail price of electricity. In places like California electricity prices are very high due to renewable generation requirements. You would definitely want to have your own solar installation before converting over to all electricity in that state.
  - DoneWithAllThat 4y ago
    We’re being forced to. After 2030 no more gas water heaters or furnaces can be sold. The cost of heating your house and water here is going to probably triple or more, and will fail every time there’s a blackout.
    - njarboe 4y ago
      You used to be able to buy water heaters that would last forever. My house had one from the 1950's with a copper tank. Still going strong. Just don't be convinced b y the repair man to get a new one when you have to replace the thermocouple every 8 years or so. The furnace is from the late 1980's, still fine. I'm not sure if such well made devices are still available for purchase however.
- SoftTalker 4y ago
  Modern residential gas furnace is 90% or more efficient.
  - 4y ago
a_square_peg 4y ago
Interesting thing here is that natural gas is about 1/3 the cost of electricity per energy unit, so when the COP is above 3, it's cheaper to heat home using heat pump. The reason why natural gas is about 1/3 of the cost of electriciy is because most natural gas power plants run at thermal efficiency of about 30%.
- pfdietz 4y ago
  Combined cycle natural gas plants have an efficiency of about 60% (lower heating value). Even simple cycle NG plants are about 40% efficient (again LHV).

onlyrealcuzzo 4y ago

In most places in the US, in normal working conditions, Heat Pumps are 30%+ cheaper than a gas furnace to run. However, in some really cold places like Chicago, Minneapolis, etc - the days where current heat pumps are inefficient might be enough to make it cheaper to always run gas. OP is proposing to have both systems and only run the gas furnace on extreme days - which would lead to a ~30% reduction in running costs. I suspect the CapEx of having two heaters wouldn't make sense, though. It'd be better to just have a hear pump that can run efficiently at colder temps.

Scoundreller 4y ago
I think it’s the opex of 2 grid connections that messes with the numbers. Depends on how your utility charges, but I feel like many/most sell you the gas roughly “at cost” and then some fixed monthly delivery/connection charge that covers their regulated rate of return on their network equity. Oil or propane supplemental heat might be cheaper than Natgas supplemental heat. My money is on wood pellet stoves for supp heat for those that don’t require full automation. Or maybe even dirty coal…
BobbyJo 4y ago
Also, the capex of gas delivery. Not needing infra to deliver gas to each and every house would likely be a pretty big win.
- bombcar 4y ago
  For new construction sure - for existing it’s already there and apparently needs little maintenance.
mrep 4y ago
You generally have an air conditioner though as well as a furnace and you can get those that can also work as a heat pump. Mine supposedly works as both but they only set it up for cooling and my gas furnace does all the heating :(
deleted 4y ago
[deleted]

Scoundreller 4y ago

Maybe the gas is cheap, but the monthly and up-front connection costs mess with the economics. And that cost will only go up as people cut the gas cord. Depends on how your utility bills out it’s infrastructure: some charge minimal monthly connection fees, others a lot. I honestly wouldn’t want to own a residential-focussed gas distribution company unless someone revolutionizes stirling engines or micro cogen systems and people start cutting their electric cord.

lizknope 4y ago
I live in a pretty standard suburban subdivision in the US. All the houses are 25 years old. I have about 60 coworkers in very similar situations. I think everyone of us has natural gas that was installed when the original company built all the homes in the subdivision over the course of a year. Stuff gets a lot cheaper when everything is put into the ground at the same time. My monthly gas connection fee is $10 so that in the summer my bill is around $19 which is $9 for the water heater and $10 for the connection fee.

kube-system 4y ago

The thing with heat pumps is that they can be as much as 300% efficient (effectively) or more. This is because they can get "free" heat from the environment. So even if per unit of energy gas is way cheaper, heat pumps can still come out ahead.

Epa095 4y ago
Modern heat pumps can be up to 500% efficient (using 1kWh of energy gives 5 kWh of heat) at optimal temperature.
- kube-system 4y ago
  Yes, I went with "300 or more" because that's a more typical number for a run-of-the-mill unit.
  - a9h74j 4y ago
    And even the low-temperature-capable heat pumps reduce toward 100% at the low temperature end, IIRC.
    - mikeyouse 4y ago
      Yep, here's a spec sheet for a unit I'm looking at as a drop-in ducted replacement for my existing system -- it has all of the models listed, but I'm looking at the 4-ton unit (12k btu per ton, so 4-ton = 48k BTU, hence the MDU18048): https://mrcool.com/wp-content/dox_repo/mc-uni-perf-ss-en-01.pdf https://mrcool.com/wp-content/dox_repo/mc-uni-perf-ss-en-01.... It takes 7kw at 17ºF to provide 48k BTU. There are 0.293W/hr per BTU so 7,000W = 25k BTU "in" and 48k BTU "out" or a COP of 1.9. At -15ºF, it's using 5.9KW but can only produce 28,500. So a COP of ~1.4. Still better than electric resistive heating but not by much. At 40ºF, the COP is more like 3.3 which is in line with the very efficient numbers. Fortunately my 99% design temp is ~8ºF and my area only sees 20hrs below zero per year, so this will work just fine for me.
anikom15 4y ago

Epa095 4y ago

Unless gas is subsidised I don't really understand how gas can be cheaper. A modern heat pump can give 3-5 kWh of heat using 1 kWh of electricity. And a modern gas generator is roughly 50% effecient at creating electricity (according to the Internet). So by using electric and a heat pump you should be able to get 1.5-2.5 times more heat from the same gas by making electricity of it first compared to burning it directly.

njarboe 4y ago
At least in the US, electricity rates and natural gas prices are highly regulated for retail customers. Thus the wholesale price of gas does not generally correlate to the retail price of electricity. In places like California electricity prices are very high due to renewable generation requirements. You would definitely want to have your own solar installation before converting over to all electricity in that state.
- DoneWithAllThat 4y ago
  We’re being forced to. After 2030 no more gas water heaters or furnaces can be sold. The cost of heating your house and water here is going to probably triple or more, and will fail every time there’s a blackout.
  - njarboe 4y ago
    You used to be able to buy water heaters that would last forever. My house had one from the 1950's with a copper tank. Still going strong. Just don't be convinced b y the repair man to get a new one when you have to replace the thermocouple every 8 years or so. The furnace is from the late 1980's, still fine. I'm not sure if such well made devices are still available for purchase however.
SoftTalker 4y ago
Modern residential gas furnace is 90% or more efficient.
- 4y ago

a_square_peg 4y ago

Interesting thing here is that natural gas is about 1/3 the cost of electricity per energy unit, so when the COP is above 3, it's cheaper to heat home using heat pump. The reason why natural gas is about 1/3 of the cost of electriciy is because most natural gas power plants run at thermal efficiency of about 30%.

pfdietz 4y ago
Combined cycle natural gas plants have an efficiency of about 60% (lower heating value). Even simple cycle NG plants are about 40% efficient (again LHV).