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Natural Gas heating is surprisingly good in practice, especially in the days where we only had fossil fuels on our electricity grid. If you go fossil fuel, you

Natural Gas heating is surprisingly good in practice, especially in the days where we only had fossil fuels on our electricity grid. If you go fossil fuel, you have only 40% efficiency for Fossil Fuel -> Electricity, then Electricity -> Traditional heat is only 100% efficient. So 100W of chemical energy turns into 40W of electricity, and then turns into 40W of heating. --------- Today, a Heat Pump can be like 200% efficient, so you 100W of chemical energy turns into 40W of electricity, then turns into 80W of heating from the heat pump. Alas, a Gas Furnace is like 90% efficient (10% of the heat escapes in the steam / waste products that needs to be pushed out the chimney, but everything else turns into home heating). So your 100W of chemical energy turns into 90W of heating, and you're done. And that's why our infrastructure in the USA is so much around gas heating, because its better. Especially since we are very rich in domestic natural gas production. Yeah, we're getting to the point where Heat Pumps + Solar Electricity are coming. But... we're not there yet. On today's grid, Natural Gas heating is likely the most efficient option. EDIT: Got my units wrong. It should be 100J of energy, not 100W of energy. Watts are power. Though in USA, we don't use Joules for energy, but instead "BTUs". Whatevs.... I think my point is still clear :-)

xxpor 4y ago
>Today, a Heat Pump can be like 200% efficient, so you 100W of chemical energy turns into 40W of electricity, then turns into 80W of heating from the heat pump. This isn't true today. The absolute minimum COP is 3.1 in the US. https://www.pickhvac.com/heat-pump/basics/cop/ https://www.pickhvac.com/heat-pump/basics/cop/
- ericpauley 4y ago
  This appears to be the minimum for geothermal. The vast majority of heat pump installs would be air source, and while these can often get 3+ it’s highly dependent on climate and local grid efficiency. It also depends on local prices. In Madison, WI our implied (not actual) electric grid efficiency based on prices is under 20%.
  - xxpor 4y ago
    The energy.gov page has more details, it's 3.3 for air source at 47 deg F and a reasonable size: https://www.energy.gov/eere/femp/incorporate-minimum-efficiency-requirements-heating-and-cooling-products-federal#airsource https://www.energy.gov/eere/femp/incorporate-minimum-efficie...
- maxerickson 4y ago
  Not for air source. Source: your link. Air source heat pumps are a lot easier, so they are the majority of installs. I expect the national code doesn't give a minimum COP for air source because the performance changes with air temperature. The bulk of my heating cost occurs when it is 10-20 ⁰F outside, where someone located in a warmer spot might have most of their heating at 35-45 or whatever.
  - xxpor 4y ago
    I definitely read it too quickly, but clicking through to the energy.gov page does clarify that the COP is measured at 47 deg F (which is warm)
- xyzzyz 4y ago
  You will not get the COP of 3 during most of the winter in the interior US with an air source heat pump. Their efficiency go down significantly once the temperature is below freezing, due to required thawing cycles, and because the bigger delta between inside and outside temperatures reduces pumping efficiency in general (efficiency is best when outside is not much colder than inside). Air source heat pumps are really good tech overall, especially because they also double up as AC in summer. However, in winter, in a head to head comparison, they only handily win in areas with mild climate, like eg. all west, or much of southern US. In the northwest or midwest, they are unlikely to beat efficient gas furnaces.
  - xxpor 4y ago
    Here's a heat pump that has a minimum COP of 2.93 at 5 F, and 9.42 (!!!!) at 47 F: https://ashp.neep.org/#!/product/56885/7/25000///0 https://ashp.neep.org/#!/product/56885/7/25000///0
    - yial 4y ago
      Your point stands, but your 1,500 sqft home needs about 68,000 btus. That heatpump would be for about a 300-400 sqft room.
      - morsch 4y ago
        Seems like a bigger one would only be more efficient.
        rgmerk 4y ago
        Surprisingly, this doesn’t seem to be true for most of the split system ductless heat pumps (aka “reverse cycle air conditioners), I’ve seen. The smallest ones are almost the most efficient ones in the range. I’m not sure why this is, and whether it generalises to house-size ducted systems, but it’s pretty striking nonetheless because it’s the exact opposite of most heat related systems I can think of.
- zrail 4y ago
  Geothermal is kind of amazing. We have a geothermal system that can get to 5.1 COP. We used 650 kWh for heat in December, which translates to 22 therms. The average household in my area uses roughly 110 therms per month for winter space heating.
  - twothamendment 4y ago
    Yup, I have a ground source heat pump, sometimes called geothermal - it is amazing! My neighbor has a slightly larger house, but close. Their bill one month was almost $500 and mine was $110. It didn't cost that much more to install and there isn't any equipment outside in the weather.
    - daydream 4y ago
      My understand was geothermal installation is extremely costly due to the deep bores you need to dig. Or do you have enough land to go out instead of down? Can you or the GP share more about the economics of your installations?
      - twothamendment 4y ago
        I've build 3 houses. For the first I had to get a bid for 3 bore holes, that was too much for me. I opted to insulate like crazy and use natural gas. I didn't bother with a bid the second time because the situation was the same. Air source was really coming along at this point (at least in the US), I should have pushed harder to get it. My current home has enough land to go horizonal. There are 4 trenches, 6 feet deep, 3 feet wide and 300 feet long. The pipe loops down and back on each trench. Excavation was about $1000 (full day for a man and a machine) and another $1000 to bury them and a day of labor to lay the plastic pipe and weld it together. Equipment was about $8,000 more than my other options (no natural gas here), but after tax breaks it was about $3000 more. I think it was worth it, even if there weren't tax breaks. I really had to push hard to get this. I had to use a general contractor on this house and he swore it wouldn't work. I made the calls and found someone to do it. The system runs often when the highs are -20f, but I've never flipped on the backup electric resistance heat. During the summer the A/C is so cheap it is practically free. It doesn't take much compared to heating. Cooling might have to get the house 30 degrees less than the outside air, but heating has to raise the house nearly 100 degrees f warmer than the outside air. Ground source is always my first recommendation, but air source should be more popular than it is. A funny note about the builder who thought ground source wouldn't work well, he also tried to talk me out of a tankless hot water heater because the well water would be too cold in the winter! I guess he didn't understand that the ground down far enough is a pretty steady temperature.
- pandaman 4y ago
  The US Code vs the Carnot's theorem, who would win? The answer might surprise you!
HDThoreaun 4y ago
But having a furnace means you also have central air. So the question isn’t furnace or heat pump, it’s furnace and one directional heat pump or just a heat pump. Yes, on cold days the furnace will be cheaper, but on most days the heat pump is cheaper and requires less maintenance since you’re turning two appliances into one.
- sokoloff 4y ago
  Many places in heating-dominated climates do not have central air. I’ve lived 35 years in New England and only one of those places (a modern high-rise) had central air.
  - HDThoreaun 4y ago
    Are we talking window unit plus radiator or just no cooling? For window + radiator heat pumps make less sense, but window unit heat pumps work well and are worth considering as a radiator replacement when the window unit is replaced.
    - sokoloff 4y ago
      Many have no cooling at all. Others have window shaker ACs only in bedrooms (which aren’t practical to use window heat pumps as a replacement for radiators since the heating balance would be terrible with the rest of the house and the air leakage around a window unit is really bad when the inside/outside delta-T is 60+°F in winter [versus ~15°F in summer])
    - dsfyu404ed 4y ago
      Window units in practice are "no cooling until there's a heat wave half way through July that prompts you to actually install them".
  - PaulDavisThe1st 4y ago
    Uhm. The entire midwest is almost as cold as New England (or colder) and yet has widely installed A/C to deal with hot humid summers. Modern (i.e. non-adobe, non-stone) construction in the higher-altitude mountain west has similar issues (without the humidity). New England is really the exception to the rule, not the rule (it's a lovely, lovely exception though).
nfriedly 4y ago
FWIW, modern heat pumps can exceed 400% efficiency, so the math is starting to work out in their favor even for fossil fuels burned at a power plant.
rainsford 4y ago
You're at the low end for heat pump efficiency, but more importantly, you're overlooking the fact that the fossil fuel usage of heat pumps benefits from the ability to use electricity generated by non-fossil fuel sources. In the US that's a significant fraction of electricity generation and in many places it's the majority of electricity. The ability to combine the electricity produced by chemical energy with nuclear, hydro, solar, wind, etc, gives heat pumps an significant advantage over directly burning fossil fuel for heat if what you care about is fossil fuel usage.
- robocat 4y ago
  Renewable fuel sources are already nearly 100% in use. So if you add electricity demand, that new demand usually comes from fossil fuel. That is, you need to consider marginal electricity generation.
  - ec109685 4y ago
    At worse, it’s replacing natural gas with fossil fuel. At best, it increases demand so more renewables are built.
    - dragontamer 4y ago
      Heating and AC are unlikely to be powered by renewables, because they're highly correlated and bursty. Ex: Your town might be fine with 100MW of power at 60F. But if the temperature drops to 40F, everyone turns on their heaters more, so the entire town uses 150MW or more. So how much renewables do you build? Not 100MW, but 150MW. Which is absurd, no one is going to overbuild capacity like that. And even at 150MW, if the temperature drops to 20F or 10F, even more energy will be used. In contrast, the Fossil Fuel / Natural Gas peaker methodology is to overbuild on capacity, because capacity is extremely cheap. Maybe the town has a 200MW plant for example. You only use what the people need, so the 200MW plant consumes 100MW at 70F, 150MW at 40F, and everyone has capacity left to grow and expand the town. ---------- Renewables are great for baseload / constant loads that are predictable. But weather isn't always predictable. In this example, 100MW of baseload renewables would be ideal, and the gas-peaker plant is used for everything in addition to that.
radicaldreamer 4y ago
You lose a lot of heat due to improper insulation or in the case of northern california, no insulation whatsoever.
cobertos 4y ago
> Alas, a Gas Furnace is like 90% efficient (10% of the heat escapes in the steam / waste products that needs to be pushed out the chimney, but everything else turns into home heating). And there exists even more efficient options today. Like high efficiency furnaces that use the heat from the flue in a second heat exchanger to bring it closer to 99%
comicjk 4y ago
> If you go fossil fuel, you have only 40% efficiency for Fossil Fuel -> Electricity, This is a big underestimate for natural gas now that we mostly use combined-cycle gas plants (basically a jet turbine bolted to the ground, with its exhaust heat used to power a traditional steam plant). Combined-cycle efficiency is over 60%, which changes your math significantly.
- chii 4y ago
  more importantly, decoupling the electricity generation with the heating, means that improvements made to electricity generation instantly flows into each home, vs using gas for home heating means _every home_ would need to purchase new gas equipment if improvements become available, to get the improvements - a major capital cost for the individual which may not be able to do it.
- m4rtink 4y ago
  Ant then you have combined cycle + district heating plants, and you use even more of the energy.
elil17 4y ago
Got all your numbers wrong too, not just your units. Modern combined cycle power plants mean that 100 J of chemical energy turn into more than 40 J of electricity (depends on your energy mix, but could be as high as 60 J). Then you also get a third of your energy from nuclear in some places, or hydro, or solar and wind (that is happening now - not just in the future). Heat pumps can be 300% or 400% efficient for most of the year (it's those few coldest nights of the year where they really struggle). So even if you don't have any nuclear or renewable energy in your mix, just natural gas, you get 60*3 or 4 = 180 to 240 J of heat energy from your 100 J of chemical energy. For most people in America, heat pumps are currently the most efficient option.
bunabhucan 4y ago
You're focusing on "today" when this is a twenty or thirty year machine. Twenty or thirty years from now a gas furnace will still be a 100% emitter. A heat pump has the ability (without upgrades) to move an increasing quantity of the energy to renewables.
_0w8t 4y ago
A modern natural gas power plant has over 60% efficiency of electricity generation. 40% is for rather old ones or those used for peak, not base load. But even those are improving. Moreover, using natural gas at home for heating is not 100% efficient. Some heat is lost with exhaust plus not everything is burned. A good furnace with proper heat exchanger is about 90%, but cheaper ones can be below 80%. So even if your electrical heat pump is just 200% efficient and the electricity comes from a gas power plant, it is already a win compared with a gas furnace at home. Both with electricity and gas there are transmission losses, but they are roughly the same and with electricity we know how to make them smaller long-term.
HyperSane 4y ago
Heat pump's coefficient of performance is more like 3 to 5.
Dork1234 4y ago
Most traditional natural gas heat is only 80% efficient since you have wasted exhaust heat. If you had a air pump you can achieve up to 92%-95% efficient, but with the added cost and complexity of having an electric fan.

xxpor 4y ago

>Today, a Heat Pump can be like 200% efficient, so you 100W of chemical energy turns into 40W of electricity, then turns into 80W of heating from the heat pump. This isn't true today. The absolute minimum COP is 3.1 in the US. https://www.pickhvac.com/heat-pump/basics/cop/ https://www.pickhvac.com/heat-pump/basics/cop/

ericpauley 4y ago
This appears to be the minimum for geothermal. The vast majority of heat pump installs would be air source, and while these can often get 3+ it’s highly dependent on climate and local grid efficiency. It also depends on local prices. In Madison, WI our implied (not actual) electric grid efficiency based on prices is under 20%.
- xxpor 4y ago
  The energy.gov page has more details, it's 3.3 for air source at 47 deg F and a reasonable size: https://www.energy.gov/eere/femp/incorporate-minimum-efficiency-requirements-heating-and-cooling-products-federal#airsource https://www.energy.gov/eere/femp/incorporate-minimum-efficie...
maxerickson 4y ago
Not for air source. Source: your link. Air source heat pumps are a lot easier, so they are the majority of installs. I expect the national code doesn't give a minimum COP for air source because the performance changes with air temperature. The bulk of my heating cost occurs when it is 10-20 ⁰F outside, where someone located in a warmer spot might have most of their heating at 35-45 or whatever.
- xxpor 4y ago
  I definitely read it too quickly, but clicking through to the energy.gov page does clarify that the COP is measured at 47 deg F (which is warm)
xyzzyz 4y ago
You will not get the COP of 3 during most of the winter in the interior US with an air source heat pump. Their efficiency go down significantly once the temperature is below freezing, due to required thawing cycles, and because the bigger delta between inside and outside temperatures reduces pumping efficiency in general (efficiency is best when outside is not much colder than inside). Air source heat pumps are really good tech overall, especially because they also double up as AC in summer. However, in winter, in a head to head comparison, they only handily win in areas with mild climate, like eg. all west, or much of southern US. In the northwest or midwest, they are unlikely to beat efficient gas furnaces.
- xxpor 4y ago
  Here's a heat pump that has a minimum COP of 2.93 at 5 F, and 9.42 (!!!!) at 47 F: https://ashp.neep.org/#!/product/56885/7/25000///0 https://ashp.neep.org/#!/product/56885/7/25000///0
  - yial 4y ago
    Your point stands, but your 1,500 sqft home needs about 68,000 btus. That heatpump would be for about a 300-400 sqft room.
    - morsch 4y ago
      Seems like a bigger one would only be more efficient.
      - rgmerk 4y ago
        Surprisingly, this doesn’t seem to be true for most of the split system ductless heat pumps (aka “reverse cycle air conditioners), I’ve seen. The smallest ones are almost the most efficient ones in the range. I’m not sure why this is, and whether it generalises to house-size ducted systems, but it’s pretty striking nonetheless because it’s the exact opposite of most heat related systems I can think of.
zrail 4y ago
Geothermal is kind of amazing. We have a geothermal system that can get to 5.1 COP. We used 650 kWh for heat in December, which translates to 22 therms. The average household in my area uses roughly 110 therms per month for winter space heating.
- twothamendment 4y ago
  Yup, I have a ground source heat pump, sometimes called geothermal - it is amazing! My neighbor has a slightly larger house, but close. Their bill one month was almost $500 and mine was $110. It didn't cost that much more to install and there isn't any equipment outside in the weather.
  - daydream 4y ago
    My understand was geothermal installation is extremely costly due to the deep bores you need to dig. Or do you have enough land to go out instead of down? Can you or the GP share more about the economics of your installations?
    - twothamendment 4y ago
      I've build 3 houses. For the first I had to get a bid for 3 bore holes, that was too much for me. I opted to insulate like crazy and use natural gas. I didn't bother with a bid the second time because the situation was the same. Air source was really coming along at this point (at least in the US), I should have pushed harder to get it. My current home has enough land to go horizonal. There are 4 trenches, 6 feet deep, 3 feet wide and 300 feet long. The pipe loops down and back on each trench. Excavation was about $1000 (full day for a man and a machine) and another $1000 to bury them and a day of labor to lay the plastic pipe and weld it together. Equipment was about $8,000 more than my other options (no natural gas here), but after tax breaks it was about $3000 more. I think it was worth it, even if there weren't tax breaks. I really had to push hard to get this. I had to use a general contractor on this house and he swore it wouldn't work. I made the calls and found someone to do it. The system runs often when the highs are -20f, but I've never flipped on the backup electric resistance heat. During the summer the A/C is so cheap it is practically free. It doesn't take much compared to heating. Cooling might have to get the house 30 degrees less than the outside air, but heating has to raise the house nearly 100 degrees f warmer than the outside air. Ground source is always my first recommendation, but air source should be more popular than it is. A funny note about the builder who thought ground source wouldn't work well, he also tried to talk me out of a tankless hot water heater because the well water would be too cold in the winter! I guess he didn't understand that the ground down far enough is a pretty steady temperature.
pandaman 4y ago
The US Code vs the Carnot's theorem, who would win? The answer might surprise you!

HDThoreaun 4y ago

But having a furnace means you also have central air. So the question isn’t furnace or heat pump, it’s furnace and one directional heat pump or just a heat pump. Yes, on cold days the furnace will be cheaper, but on most days the heat pump is cheaper and requires less maintenance since you’re turning two appliances into one.

sokoloff 4y ago
Many places in heating-dominated climates do not have central air. I’ve lived 35 years in New England and only one of those places (a modern high-rise) had central air.
- HDThoreaun 4y ago
  Are we talking window unit plus radiator or just no cooling? For window + radiator heat pumps make less sense, but window unit heat pumps work well and are worth considering as a radiator replacement when the window unit is replaced.
  - sokoloff 4y ago
    Many have no cooling at all. Others have window shaker ACs only in bedrooms (which aren’t practical to use window heat pumps as a replacement for radiators since the heating balance would be terrible with the rest of the house and the air leakage around a window unit is really bad when the inside/outside delta-T is 60+°F in winter [versus ~15°F in summer])
  - dsfyu404ed 4y ago
    Window units in practice are "no cooling until there's a heat wave half way through July that prompts you to actually install them".
- PaulDavisThe1st 4y ago
  Uhm. The entire midwest is almost as cold as New England (or colder) and yet has widely installed A/C to deal with hot humid summers. Modern (i.e. non-adobe, non-stone) construction in the higher-altitude mountain west has similar issues (without the humidity). New England is really the exception to the rule, not the rule (it's a lovely, lovely exception though).

nfriedly 4y ago

FWIW, modern heat pumps can exceed 400% efficiency, so the math is starting to work out in their favor even for fossil fuels burned at a power plant.

rainsford 4y ago

You're at the low end for heat pump efficiency, but more importantly, you're overlooking the fact that the fossil fuel usage of heat pumps benefits from the ability to use electricity generated by non-fossil fuel sources. In the US that's a significant fraction of electricity generation and in many places it's the majority of electricity. The ability to combine the electricity produced by chemical energy with nuclear, hydro, solar, wind, etc, gives heat pumps an significant advantage over directly burning fossil fuel for heat if what you care about is fossil fuel usage.

robocat 4y ago
Renewable fuel sources are already nearly 100% in use. So if you add electricity demand, that new demand usually comes from fossil fuel. That is, you need to consider marginal electricity generation.
- ec109685 4y ago
  At worse, it’s replacing natural gas with fossil fuel. At best, it increases demand so more renewables are built.
  - dragontamer 4y ago
    Heating and AC are unlikely to be powered by renewables, because they're highly correlated and bursty. Ex: Your town might be fine with 100MW of power at 60F. But if the temperature drops to 40F, everyone turns on their heaters more, so the entire town uses 150MW or more. So how much renewables do you build? Not 100MW, but 150MW. Which is absurd, no one is going to overbuild capacity like that. And even at 150MW, if the temperature drops to 20F or 10F, even more energy will be used. In contrast, the Fossil Fuel / Natural Gas peaker methodology is to overbuild on capacity, because capacity is extremely cheap. Maybe the town has a 200MW plant for example. You only use what the people need, so the 200MW plant consumes 100MW at 70F, 150MW at 40F, and everyone has capacity left to grow and expand the town. ---------- Renewables are great for baseload / constant loads that are predictable. But weather isn't always predictable. In this example, 100MW of baseload renewables would be ideal, and the gas-peaker plant is used for everything in addition to that.

radicaldreamer 4y ago

You lose a lot of heat due to improper insulation or in the case of northern california, no insulation whatsoever.

cobertos 4y ago

> Alas, a Gas Furnace is like 90% efficient (10% of the heat escapes in the steam / waste products that needs to be pushed out the chimney, but everything else turns into home heating). And there exists even more efficient options today. Like high efficiency furnaces that use the heat from the flue in a second heat exchanger to bring it closer to 99%

comicjk 4y ago

> If you go fossil fuel, you have only 40% efficiency for Fossil Fuel -> Electricity, This is a big underestimate for natural gas now that we mostly use combined-cycle gas plants (basically a jet turbine bolted to the ground, with its exhaust heat used to power a traditional steam plant). Combined-cycle efficiency is over 60%, which changes your math significantly.

chii 4y ago
more importantly, decoupling the electricity generation with the heating, means that improvements made to electricity generation instantly flows into each home, vs using gas for home heating means _every home_ would need to purchase new gas equipment if improvements become available, to get the improvements - a major capital cost for the individual which may not be able to do it.
m4rtink 4y ago
Ant then you have combined cycle + district heating plants, and you use even more of the energy.

elil17 4y ago

Got all your numbers wrong too, not just your units. Modern combined cycle power plants mean that 100 J of chemical energy turn into more than 40 J of electricity (depends on your energy mix, but could be as high as 60 J). Then you also get a third of your energy from nuclear in some places, or hydro, or solar and wind (that is happening now - not just in the future). Heat pumps can be 300% or 400% efficient for most of the year (it's those few coldest nights of the year where they really struggle). So even if you don't have any nuclear or renewable energy in your mix, just natural gas, you get 60*3 or 4 = 180 to 240 J of heat energy from your 100 J of chemical energy. For most people in America, heat pumps are currently the most efficient option.

bunabhucan 4y ago

You're focusing on "today" when this is a twenty or thirty year machine. Twenty or thirty years from now a gas furnace will still be a 100% emitter. A heat pump has the ability (without upgrades) to move an increasing quantity of the energy to renewables.

_0w8t 4y ago

A modern natural gas power plant has over 60% efficiency of electricity generation. 40% is for rather old ones or those used for peak, not base load. But even those are improving. Moreover, using natural gas at home for heating is not 100% efficient. Some heat is lost with exhaust plus not everything is burned. A good furnace with proper heat exchanger is about 90%, but cheaper ones can be below 80%. So even if your electrical heat pump is just 200% efficient and the electricity comes from a gas power plant, it is already a win compared with a gas furnace at home. Both with electricity and gas there are transmission losses, but they are roughly the same and with electricity we know how to make them smaller long-term.

HyperSane 4y ago

Heat pump's coefficient of performance is more like 3 to 5.

Dork1234 4y ago

Most traditional natural gas heat is only 80% efficient since you have wasted exhaust heat. If you had a air pump you can achieve up to 92%-95% efficient, but with the added cost and complexity of having an electric fan.