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Comment by SigmundA | Hacker News Reader

They can be, natural gas is about 1000 BTU per cubic foot.

An expensive high efficiency gas furnace might be 95% efficient (most normal furnaces are in the 80's)

1000 x 0.95 = 950 BTU/cuft

A high efficiency natural gas power plant is 60% efficient and a modern high efficiency low temp heat pump can have a COP up to around 2.7 at 17F

1000 x 0.6 x 2.7 = 1620 BTU/cuft

A 40% power pant is still more efficient than a 95% furnace with a 2.7 COP heat pump.

There is obviously more to this, there are some grid losses to account for but has to be compared to piping losses, there is also cost factors and also how much renewable is mixed into your grid supply, but generally once that heat pump is above around 2.5 COP it starts to make sense, this is a no brainer in milder climates which is why I have a heat pump and no gas furnace here in FL even though I have gas to the house for other uses.

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> this is a no brainer in milder climates which is why I have a heat pump and no gas furnace here in FL even though I have gas to the house for other uses.

They're a no-brainer in every climate. Newer heat pumps can handle fairly cold temperatures (-13°F) pretty easily, there may be a loss in efficiency but in the majority of the world it doesn't stay that cold. A few days of lower than normal efficiency, and at worst plugging in a few space heaters if it gets extremely cold for a day or two, does not change the overall math of heat pumps being a better solution.

Hell, that's just me talking about air source heat pumps. No reason for new construction to not use ground source and get better efficiency and not worry about ambient outdoor temperatures.

Ok! I am genuinely interested in how heat pumps are more efficient. My online search led me to calling heat pumps more efficient when compared to electric heaters. And better in other ways compared to gas burners. But lord's sake, they were all upselling marketing sites for heat pumps.

I am looking for genuine research, and not from paid mouth pieces.

Majority of the comments here seem like agents of heat pump industry. And HN rules forbid me from calling them that.

Just do the math, all you need to know is furnace efficiency and COP of the heat pump along with the efficiency of your local power plant. I did that in my post, its not super complicated.

Gas is burned creating a certain amount of heat, in a furnace some is lost to exhaust the rest goes into your house. That is the furnace efficiency.

When gas is burned at a power plant the same number of BTU is released, but it is used instead in a heat engine to create mechanical power which is then turned into electrical power, the rest is lost to exhaust, this is the power plant efficiency.

Heat pumps are over 100% efficient because they capture heat from the environment around your house which is warmed by the sun. So even though more energy is lost in creating electricity than burning directly in your house, this is more than made up for by using the ambient heat around your house, it is essentially solar assisted (in the case of air source).

Physics. When combusting fuel you cannot get more heat energy out of them than the chemical bonds you are breaking contains, a gas furnace can never be more than 100% efficient, the best commercially available ones are 95%, and a majority that are actually installed are closer to 80-90%.

Heat pumps do not create heat, the refrigeration cycle moves heat from point A to point B. For every KWh of electricity used by your refrigerator, air conditioner, or heat pump, 3-4 KWh of heat energy can be moved where you want it to go.

Even if you have a (comparatively) inefficient combined cycle natural gas power plant that is 50-60% efficient, you're still getting 150-200% efficiency for heating with a heat pump compared to 80-95% for a natural gas furnace.

I live in Boise so we have pretty cheap utilities compared to the national average, but here's some math:

1 therm (~30KWh of energy) is ~$0.72 from Intermountain Gas, the furnace in my rental is 90% efficient, so I actually get 27KWh of heat from every therm I burn.

Idaho power has a tiered tariff for residential customers, with a peak charge of ~$0.098 per KWh during the winter for usage over 2,000 KWh in a month.

Every therm my gas furnace burns costs me as much as ~7.5KWh from the electric utility, but those 7.5KWh can provide me with 30KWh of heat with a quality heat pump, which would require a 100% efficient natural gas furnace to reach. Add in that gas furnaces have a much higher TCO because of maintenance and repair compared to a heat pump, and they're not just energy inefficient in comparison but even just plain more expensive to operate even with incredibly cheap fossil fuels.

Did you watch the video linked on the highest rated post on this thread? The one from technology connections? It explains it all very well.

I am happy you have an open mind, but the fact that you are trying to tear the technology down when you apparently have no idea how it works or what it even is- hopefully you realize that it is also used for air conditioning, and is essentially just an air conditioner running in reverse... I hope this is a learning experience for you.

At the very least it gives me hope that those trying to tear down this technology are just ignorant, I had real suspicions that they were agents of the fossil fuel industry, or this was something Fox News and the like decided to target and is now being parroted.

So heat pumps do lose efficiency at lower temperature such as -13F but the much bigger issues is loss of capacity. If you look at the curve of available heating capacity of a heat pump versus the heating needs for your house that tend to be a bit of a mirror image. When it is warmer out your house needs less heat but heat pumps have the highest capacity they will have. As temps drop the house will require more heat while the capacity of the heat pump is dropping.

That isn't to say they cannot work I personally have a heat pump in my house and it worked fine through the -15F weather we got. But it requires careful design work initially. Also you run into simply size constraints where residential heat pumps tend to max out at 5 tons (60k BTUs) typically when furnaces can easily get up into the 100k+ BTUs. Which might require multiple heat pumps and separating existing duct work. But definitely new construction should start designing around these constraints now.

> Which might require multiple heat pumps and separating existing duct work. But definitely new construction should start designing around these constraints now.

Ductless mini-splits remain an option as well. I'd actually like to see somebody make some ground-source exchanger that ductless heads could connect to, because they're much cheaper to install than a multi-zone ducted system.

They make systems like that but they tend to be more commercial systems. You could get a ground to water heat pump then run chilled/heated water to the mini split heads depending on what they are calling for but even that is pushing into commercial territory. And sadly with commercial HVAC comes significantly higher prices.

In cold climates, systems have backup electric furnaces.

I am in NY. And I think for Florida, a heat pump makes because of a hybrid AC model. Even if electricity is more expensive, the equipment and energy cost of a separate unit is not worth spending.

In extreme climates, gas burning is cheaper. And quite clean. There are some objections because of delivery leaks, but that is a separate concern.

As pointed out by several other comments, you're very off base about heat pump efficiency and about natural gas being "clean."

Switching everyone to heat pumps would lower emissions from heating and cooling in the US by 160m tonnes a year [1], which is something like 30-40%.

It's true that upfront costs of heat pumps can be higher, but thanks to the IRA there are huge subsidies available (and further subsidies in many states) which make up most or even all of that difference. The lifetime costs of heat pumps with these subsidies should be substantially lower than high efficiency natural gas furnaces.

[1] https://www.rewiringamerica.org/circuit-breakers-heat-pumps

(Those subsidies, by the way, are one of the reasons "everybody is talking about heat pumps")

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