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Comment by rayiner | Hacker News Reader

I don’t know where this person is, but electricity is wildly expensive in many places. On a cold day, a good heat pump might give you say a COP of 2. So with 5 kW, you get out 10 kW of heat, or 35,000 BTU/hour. In say MA, at $0.25 per kWh retail, that’s $1.25/hour. In Boston, natural gas costs $1.5/therm, which is 100,000 BTUs. With a 96% efficient condensing boiler, you’re looking at $0.55/hour for the same 35,000 BTU/hour output, or less than half the price.

To be comparable to natural gas, you need electricity to be about $0.10 per kWh retail. That’s basically the PNW, the mountain west, and parts of the Deep South.

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After I installed a high-COP, cold-climate heat pump in my Boston area house in 2020, I figured the wintertime running cost was about half again the cost of gas heat. However, the cost was about the same as that of running the somewhat ancient oil furnace the house came with.

Electricity prices in MA are high and are controlled by the marginal cost of gas to run generators, even though we have a significant fraction of renewable, hydro, and nuclear generation. Gas prices are also high because we're at the far end of the east coast natural gas pipeline network.

It's interesting to think about the whole chain -- burning gas in a high efficiency condensing furnace at home approaches 100% efficiency of conversion from chemical to heat energy.

Whereas utility generators that convert heat to electricity are upper bounded by the second law to ~60% efficiency, and then you have transmission losses on top of that. But you win roughly all that lossage back because your heat pump can pump ~3 units of outdoor heat energy into your house for every ~1 unit of electrical energy it consumes.

Add transmission costs and unfortunately heat pumps are more expensive here for now. But CO2 wise of course it still wins because of that renewal and nuclear share I talked about

More importantly, I can also install solar and start getting some energy "for free" (obviously, much more so in the summer than in the winter). And over time of course our renewable share will go up.

PG&E is basically California, where it can hit north of $0.50/kWh pretty regularly.

I think it's worth noting in this article too that the author mentions they can now heat and cool parts of their house they weren't previously, so I'm gonna guess their actual usage went up and this is basically surprise for no reason.

If you look at the thermal design of a house, this strategy doesn't make a lot of sense. There's no thermal barriers between rooms, and plenty of airflow if the HVAC circulation is functioning.

Cost of 1 therm from pg&e is $2.66 so variable speed heat pump can still be cheaper

You really need to be calculating costs based on seasonal performance (SCOP) which is going to depend on your area. In my climate the worst case COP is around 2, but the seasonal performance of an air-to-water heat pump would be between 3.5 and 5, depending on various factors.

Granted it doesn't make a difference in your example because your gas is cheap at $0.05/kWh, but for me (EU), the price for natural gas would be around $0.11/kWh while electricity is around $0.25/kWh.

> To be comparable to natural gas, you need electricity to be about $0.10 per kWh retail. That’s basically the PNW, the mountain west, and parts of the Deep South.

Shouldn't that also take into account the variations in natural gas prices?

For example electricity in Delaware is more expensive than electricity in Washington, but so is natural gas by about the same percentage. Same when comparing Kansas to Washington.

Using natural gas rates by state from here [1] and electricity rates by state from here [2], here are the states where the ratio of natural gas price to electricity price is higher than that of Oregon and so should be places where you have the best chance to same money switching from gas to electric. The second column is the price ratio.

  Georgia         3.3
  Oklahoma        3.2
  Ohio            3.1
  Florida         2.9
  West Virginia   2.9
  Texas           2.7
  Kentucky        2.6
  Louisiana       2.5
  Delaware        2.4
  Missouri        2.3
  Wyoming         2.3
  Mississippi     2.3
  Washington      2.2
  Kansas          2.2
  North Dakota    2.2
  Arizona         2.2
  North Carolina  2.1
  Arkansas        2.1
  Alabama         2.0
  South Carolina  1.9
  Virginia        1.9
  Indiana         1.9
  Oregon          1.9

[1] https://www.chooseenergy.com/data-center/natural-gas-rates-b...

[2] https://www.electricchoice.com/electricity-prices-by-state/

> To be comparable to natural gas, you need electricity to be about $0.10 per kWh retail. That’s basically the PNW, the mountain west, and parts of the Deep South.

I think Chicago is pretty close? Abundant nuclear is great.

In the Seattle area we're up to $0.13-0.14/kWh, but also rarely see the kinds of cold temperatures that lead to low COP figures.

That's on a very cold day. Depending where you are they may be more common or not. But in the UK, they're pretty uncommon. COP of ~4 is much more common.

https://www.pv-magazine.com/2023/03/17/field-data-on-heat-pu...

Some data from a U.K. funded study suggested the median was 2.44 here in winter and 2.8 not in winter.

The information you are looking for can be found in the article.

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