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THINKFR33LY t1_j5j8iio wrote

Reply to comment by MajorProblem50 in Monthly Electricity Bill Is Killing Me by haitiandev

They're not fully efficient down to -15. They can produce heat all the at that temp, but they're going to use much more power than at 30f for example.

I have the newest bosch heat pumps. With oil at $4 and electrical at north of 45c with delivery fees, a heat pump with a cop of 3 or so is more expensive than oil with sub freezing temps outside.

The most efficient Mitsubishi mini split might extend that down to the 20s, but def not -15.

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techorules t1_j5kvj3v wrote

Maybe not "Fully" efficient but my Mitsu Hyper Heat Pump has a COP of 1.7 at -15 F. So even at those temperatures it can beat out other fuel types depending on prices. For instance for a propane customer even with a fairly high electric rate per kWh would still beat out propane. Probably oil too.

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langjie t1_j5l14ap wrote

3412 btu/kwh x 1.7 COP = 5,800 btus.

oil at $4 /gal: 138,700 btus * 80% boiler efficiency = 110,960 btu's (19.1 kwh of heat pump). electricity needs to be at 21 cents/kwh to be equal to $4 oil if outside is @ -15°F

propane at $2.5 /gal: 91,700 btus * 80% boiler efficiency = 73,360 btu's (12.6 kwh of heat pump). electricity needs to be at 20 cents /kwh to be equal to $2.50 propane if outside is -15°F

all depends on the rate but also it's typically not that cold out so the math changes with increased efficiency

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techorules t1_j5l3wyu wrote

Cool. Yeah my electricity is way below those figures..... Also propane averages in Mass are way way higher than $2.5. My last delivery (which I am hoping I literally my last ever) was over $4. And with climate change sadly -15F is pretty rare indeed.

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