That’s a perfectly normal number for any home that isn’t very new and perfectly insulated.
My 37sqm appartment needs approximately 5000 kWh in natural gas per year, 876 kWh last December, so 28 kWh per day on average. The building is admittedly old and not perfectly insulated but it’s also not a log cabin out in the open in Finland, but instead a flat enclosed within 3 other flats in the middle of cosy, never below -8C Germany.
21 kWh in a log cabin in Finnland actually seemed pretty low to me. It’s sort of obvious OP is using a heat pump and the cabin must really be absolutely tiny.
It’s an easy conversion - 1 kWh is equal to 3412 Btus. In Germany, both electricity and natural gas are charged in kWh. I know a fair bit about energy measurement if you have any questions.
Great question. When it comes to utility billing, efficiency doesn’t factor at all. Just like with electric billing, the utility company gives zero shits about what you do with your energy. They just bill you for everything you use.
Utility companies keep track of the volume used in cubic meters and convert it to kWh using the formula…
Volume (in cubic meters) • Calorific value (usually around 37-42) • 1.02264 (correction factor) ÷ 3.6 (conversion factor to kWh) = kWh
The calorific value accounts for the varying energy density of natural gas caused by its inconsistent composition. The correction factor accounts for the effects of the average temperature and pressure at the property on gas volume measurement. 1.02264 is standard for most locations but would be different if the location is extreme, like the high elevation of Machu Picchu.
What sucks about gas heating is some of the heat energy released leaves with the exhaust. The heating efficiency varies depending on the unit but is generally 90-95% for newer units but as low as 50% for older units. While 90-95% doesn’t seem bad, electric heat pumps achieve efficiencies that exceed 100%, even as high as 300+%.
So given that most gas furnaces (at least in the US) operate at 90-95% efficiency, does that mean 20 kWh of resistive electric heat (as measured on the bill) provides similar heat to ~11 kWh of gas?
Cubic meters (or another similar measure of volume) is what I’d expect. It’s the conversion to an unrelated and theoretical (since it’s not actually being converted to electricity) unit that confuses me. I presume it’s to make it easier to compare electric vs gas heat, but the variable efficiency of burning gas and the existence of heat pumps ruin that.
kWh is a unit of energy. Regardless of whether it is in the form of electricity or from burning fuel. So it is actually very related, and much more useful than a measurement of volume I’d argue. The measurement is of course done in m³, but then a conversion factor based on several factors is used to convert to an actually useful unit.
A m³ of gas really could be anything depending on pressure, temperature and constituents.
(Brace yourself for Much 'Merica) Several gas utilities I’ve had in the USA measure natural gas CCF, which is 100 cubic feet (at some standard temperature/pressure), which happens to be almost exactly the same as a Therm, or 100,000 BTU.
50kWh and closer to 90kWh on days like this. It’s a log cabin and I’m keeping my root cellar and insulated shed above freezing aswell. Even running a 1kW heater all day would result in a consumption more than 21kWh and that wouldn’t keep any house warm.
1kw is a small heater. 0.8kw is a tiny one. 0.8x24 is 19.2. Assuming they have other basic appliances, that’s already more than enough to account for their usage.
I’ve got a small 1200w heater that kicks on in the morning to bring the living room space up to 69. I live in a 40 year old house that’s insulated fairly well (I just had the attic redone last year to r-49) and it’s 45f outside right now. That little heater has used 6kWh since kicking on this morning getting the house up from 63f to the near 69 it is now.
On a day below freezing that heater will got for a lot longer through the day to keep temps up.
A space heater has an efficiency of close to 100%, heat pumps have at worst 100% and at best somewhere between 300 and 500%. Granted, in -35C environments, it’s probably very close to 100%, but that’s the absolute worst case, and an anomaly even in Finland.
What are you smoking? Space heaters gulp down electricity with the smallest ones running at hundreds of watts and standard ones around 1-2 kilowatts. The only ways a space heater is more efficient is if either you’re spending a shitton of energy heating rooms you aren’t in or if your homes heating system is in bad need of repair/replacement
All space heaters operate at the same efficiency since they convert electricity to heat via resistance. You may have a small one and low electricity rates in your area to see a negligible change. Or maybe other uses went down and masked the increase from the space heater usage.
Bruh I don’t think you understand how electricity consumption works.
A space heater will pull a given wattage, say 1000 watts for a pretty common one. Electric heaters are 100% efficient meaning 100% of the energy going in is converted to heat, so running that 1000 watt space heater for 1 hour will consume 1000 watt-hours (or 1 kilowatt hour) and heat the space by exactly 1000 watts or 1 kilowatt (kilo meaning thousand)
Plugging this into a electric bill calculator, at a common $0.15/kWh running that 1000 watt space heater 24/7 will cost about $100 per month
If your space heater is so insanely awesome, please do tell me, what’s your electric rate and the wattage of the heater?
Bruh, I don’t think you understand that heating a room is cheaper than heating your whole house. If I ran my space heater 24/7, I’d be sweating all day. If I run my central heater 24/7, my house barely reaches the temperature my room does before I turn my space heater off.
My electric bill is ~$160 when running the central heater. It’s ~$80 when I run my space heater.
As always, I encourage people to see for themselves rather than trusting strangers on the internet.
Experience is better than theory, every time. I feel sorry for the people who will avoid saving money because of comments like yours.
To quote my earlier comment with emphasis this time:
The only ways a space heater is more efficient is if either you’re spending a shitton of energy heating rooms you aren’t in or if your homes heating system is in bad need of repair/replacement
So you’ve already agreed with my original point, because you reduced power consumption by turning your HVAC down and using a space heater to heat just the room you’re in. Running a 4 kilowatt central heater will use more electricity as it runs than a 1 kilowatt space heater. But a 1 kilowatt space heater is still pulling down a kilowatt to run (which is a lot!)
Experience is better than theory, every time. I feel sorry for the people who will avoid saving money because of comments like yours.
YOU CAN LITERALLY CALCULATE THIS! Watts consumed by the heating source multiplied by number of hours per month it runs gives you the watt hours for power consumption, bigger number means bigger bill. In fact it’s important to calculate it first because electric bills will naturally fluctuate and be difficult to identify the changes in consumption due to being an aggregate of everything in your home combined with outside temperature fluctuations.
This is such an outdated information. Modern heatpumps work just fine even in temperatures of -20C and below. Ofcourse the efficiency gets worse the colder it is but even at worst it’s still 100% efficient. On a typical year there’s only a handful of really cold days. It doesn’t make sense not to get a heatpump just because it’s inefficient for few days. It’s not like it stops heating or something. It just effectively turns into electric radiator which is what my house was heated with before I got the heatpump anyways.
This is true only if you have a heat pump with electric/resistive backup heat. But for some reason, it’s pretty easy to buy one in the US that doesn’t. (Which is where I assume that poster is, because most anti-heat-pump sentiment seems to come from here.)
Not quite, in my experience on really cold days my heat pump struggles to keep up. This is expecially true when the outside unit is frosting up. The unit has to reverse and pump heat out of the house.
That’s one of the reasons i run my wood pellet stove on those days. The secondary source of heat takes the load off the heat pump.
Sure, but as I said it’s just a handfull of days in a year. If the heatpump alone struggles to keep my house warm I can just switch on one or two electric radiators.
In an area that gets very cold, a geothermal heat pump (which uses the ground rather than the air for heat exchange) would work better than an air-source heat pump. More expensive to install though, and you need a good amount of land
It’s basically what modern homes should have built below them. Then it doesn’t need extra space. Wonder if it’s already enough to put some pipes a meter below the basement?
Most heat pumps will use the aux coils to defrost. It’s also ok for the heat pump to literally run 24/7 if it needs to. A lot of people freak out when the heat pump runs all day and blows “cool” 80F at from the vents, but it’s still working as intended. Though I totally get how that can make a place feel “drafty” without some backup running
It’s true they’re at worst 100% efficient, but they’re also typically sized lower than resistive electric heaters in terms of input power. In the US, a residential heat pump likely draws about 4kW, whereas resistive heat strips or baseboard heating could be multiples of that. As an air source heat pump’s output drops on very cold days, a unit rated for e.g. 48000BTU/hr at 47°f might produce only half of that at 5°f/-15c. A “good” unit here would produce perhaps 75%. The way we do HVAC sizing, unless you radically oversized the system for most weather (including air conditioning) you’ll need a backup source of heat on the coldest days.
Code (law specifying how much heating / cooling capacity is required in normal worst-case weather conditions) where I live would require me to use about 2x the normal sizing to achieve pure heat pump heating at the required design temperature (around 5f/-15c). That means at the peak of summer (about 100f/38c) the unit would be operating at less than half of its full cooling capacity.
It’s non-sensical to base the cost effectiveness of a heat pump on the handful of really cold days when it’s no more efficient than electric resistive heating. You have to take into account the entire heating season. Electric resistive heating is allways 100% efficient. Air sourced heat pump is 100% efficient in the worst possible conditions. In normal conditions it’s from 300% to 500% efficient. While your 650 watt space heater puts out heat at the constant rate of 650 watts, a heat pump outputs 3000 watts worth of heat while using that same 650 watts of energy.
I live in a very cold part of the world where the temps can easily exceed your -20C for night times for several weeks at a time. And even as the daily high for a week stretch or two over a winter. And while I could have purchased a heat pump that would work to that low of a temperature, it would have cost over twice the price. Going from $5000US installed to over $10,000US for just the heat pump. And that included the rebate incentives.
My heat pump is set to set to cut out and switch to LP heat at -10C because it becomes cheaper to run an LP furnace at that point - cost of electricity = 6.5 cents per kilowatt hour vs $1.75US gallon LP. The loss of efficiency matters to my pocket book. And I chose my particular heat pump with my advice of my Daughter who has a PhD in ME and works as a research engineer for a non-profit studying HVAC systems and the efficiencies of the technology used in them. And she won’t install a heat pump in her house because for where she lives, they literally do not make financial sense. There is zero savings to be had with switching from natural gas heat to electric.
So installing a heat pump is not a universal no brainer. You still need to to the math to see if it pays.
Yeah obviously it’s a whole different game when you live in a place like that. That’s just quite rare usecase. The vast majority of people who keep repeating the “heatpumps don’t work in cold climates” lives in a climate much warmer than I do. Even mine struggles on the really cold days we get few times a year but that’s fine because it gets the job done flawlessly for the remaining 350 days.
My issue with these arguments is the blanket statements that get made. Both arguments on this particular subject can both be true at the same time. And until you do the math for your specific situation, you can’t tell if it pays until you know the answer
Now, I believe it works out for you just as it does for me. But I had to the math to figure it out to know for sure. Most people who argue over this subject have never done the math.
If your intention is to heat or cool air using as little electricity as possible, a basic heat pump split air conditioning unit is going to be more than adequate for 90% of people. If you live in a place like Yakutsk, then yeah, you probably need to look into something else, but for the vast majority of people it’s going to be just fine. A general recommendation doesn’t mean it’s the best choice for literally every single person.
But it very often catches many who simply take it as an irrefutable truth.
As I gave as an example, my one Daughter who is recognized by her peers as an expert in this field, and is all about improved efficiency and renewable energy, did the math and found that it doesn’t work for her. And it’s not because she lives in a terrible climate - it’s warmer and varies less than where I live by a noticeable amount. It’s because when you compare total costs, over the life span of a heat pump, she would end up paying extra to have one verses a simple natural gas furnace. It would be even sillier for my neighbor who is a logger. He uses 100% wood heat. Because he can literally harvest, process, and store enough firewood for several years in one afternoon. Anything else is far more expensive. But the math says it works for me.
You can’t make general statements about 90% of all people until everyone does the math. This is just one of the field studies my Daughter is doing. Trying to collect enough real time data on real homes and families and doing the math to help pinpoint locations where it makes sense and where it does not make sense at this time. It does not always workout like you and I might think it would.
In very cold climates, having a hybrid system like the one you’re describing is that universal no brainer in my opinion. Especially since most cold regions also typically have really long transitional periods where your heat pump is most efficient and pays itself off fastest. Combining that with turning it off during harsh winter weeks gives you the best of both worlds.
It’s not even a no brainer even then. You absolutely need to actually do the math for your particular situation to make that determination. For me it works out. For my neighbor down the road who is a logger, it does not. He can harvest, process, and store 2 years worth of firewood in a mere handful of hours. Any other heat source makes little sense for him.
I am also an engineer and used to have LP backup heat and the only way the LP is cheaper per BTU is if you rapidly deprecate the heat pump asset.
A gallon of propane has 91,000 BTU, and a kWh of electricity has 3400 BTU. 91k/3.4k ~ 26kWh x 0.065 ~ $1.73 for electricity equivalent at 1.0 coefficient of performance. But your COP is likely around 2-3, so the heat pump will be at least 2x cheaper than the LP. It would take like 6000 hours of operation to break even on the bigger heat pump, and that’s ignoring the cost and maintenance of the propane furnace
There are heat pumps that exchange heat with the ground. Those can function well in more extreme temperatures. Also you could/should have alternative heating methods for extreme situations even if they are much more inneficient
Have you actually priced such systems and the payback time vs heat pumps vs petroleum sourced heat?
I know one person who chose a mix of ground heat pump, LP, and wood heat. He told me that it only had a reasonable payback was because he was building a new home and the extra cost could be tagged to the total build cost. Making it cheaper than a retro fit. He said it added another $25,000 to the cost of his new home. But in fairness, he does enjoy it.
I only do the refrigeration side of things and I don’t do residential stuff so I’m not sure on exact pricing. Pricing will also vary greatly depending on the exact area. For example in my area we have a high enough ground water level that open loop geothermal is easy and that is the cheapest/easiest method of geothermal. The other types will also vary in cost depending on soil type and moisture content because that will partially dictate how big of a ground loop you need. The amount of area you have for a ground loop will also be a big factor because if you don’t have enough yard area for a horizontal loop then you need to use a vertical loop which can be heniously expensive.
As far as payback goes they are far more expensive to install regardless of the type but the ground loop (assuming closed loop system) can easily last over 50 years and that is the most expensive part of the whole system by a large margin. Out of the $25,000 you mentioned I would bet that about $20,000 of that was just for the ground loop. The rest of the system is going to be more durable as well due to not being outdoors. The expected lifespan of the other components is 20 years and they can easily last far longer than that. So the energy savings is only part of the cost savings. The other part is that geothermal heat pumps need practically no maintenance and break down far more rarely than any other conventional heating or cooling solution. With how long they last and how durable they are a geothermal heat pump can probably pay itself off just with avoided service calls.
The biggest issue is if you don’t have the money to buy it, it matters very little about the efficiency and how long it lasts. You still need to pay for it. He could justify the expense because we are a very rural area and land is cheap and tagging it to a new build brings down the interest costs. This is often makes geo-thermal a non-starter for most - as you point out. He even admits he wouldn’t have done it under any other circumstance.
How are you using 21kWh/day heating a small home? Do you have any insulation at all?
Probably because it’s about -35C outside.
Dude is basically living on the set of The Thing at this point.
That’s a perfectly normal number for any home that isn’t very new and perfectly insulated.
My 37sqm appartment needs approximately 5000 kWh in natural gas per year, 876 kWh last December, so 28 kWh per day on average. The building is admittedly old and not perfectly insulated but it’s also not a log cabin out in the open in Finland, but instead a flat enclosed within 3 other flats in the middle of cosy, never below -8C Germany.
21 kWh in a log cabin in Finnland actually seemed pretty low to me. It’s sort of obvious OP is using a heat pump and the cabin must really be absolutely tiny.
Why are you measuring natural gas in kWh? How do you even measure that as such?
It’s an easy conversion - 1 kWh is equal to 3412 Btus. In Germany, both electricity and natural gas are charged in kWh. I know a fair bit about energy measurement if you have any questions.
This is fascinating to me. How does it factor efficiency, since gas needs to be burned?
Great question. When it comes to utility billing, efficiency doesn’t factor at all. Just like with electric billing, the utility company gives zero shits about what you do with your energy. They just bill you for everything you use.
Utility companies keep track of the volume used in cubic meters and convert it to kWh using the formula…
Volume (in cubic meters) • Calorific value (usually around 37-42) • 1.02264 (correction factor) ÷ 3.6 (conversion factor to kWh) = kWh
The calorific value accounts for the varying energy density of natural gas caused by its inconsistent composition. The correction factor accounts for the effects of the average temperature and pressure at the property on gas volume measurement. 1.02264 is standard for most locations but would be different if the location is extreme, like the high elevation of Machu Picchu.
What sucks about gas heating is some of the heat energy released leaves with the exhaust. The heating efficiency varies depending on the unit but is generally 90-95% for newer units but as low as 50% for older units. While 90-95% doesn’t seem bad, electric heat pumps achieve efficiencies that exceed 100%, even as high as 300+%.
To turn gas to electricity assume 50% efficiency. 2MWh of gas = 1MWh of electricity.
So given that most gas furnaces (at least in the US) operate at 90-95% efficiency, does that mean 20 kWh of resistive electric heat (as measured on the bill) provides similar heat to ~11 kWh of gas?
It would equal about 22kWh of gas, since gas isn’t 100% efficient like electric heat is.
Ah. 50% efficency to turn gas into electricity.
If you are just making heat then burning gas directly is much better.
Energy is energy regardless of what unit is used to show it. so 3412 BTUs always equals 1kWh.
You do an efficiency calculation after, average gas blower is about 90% so you’d end up with 3070 BTUs or 0.9kWh of heat energy.
It does not factor efficiency at all.
The bill does not care about efficiency.
Very common in countries that use the metric system (ie literally everywhere except the USA). It’s measured either in kWh or in m^3
Cubic meters (or another similar measure of volume) is what I’d expect. It’s the conversion to an unrelated and theoretical (since it’s not actually being converted to electricity) unit that confuses me. I presume it’s to make it easier to compare electric vs gas heat, but the variable efficiency of burning gas and the existence of heat pumps ruin that.
kWh is a unit of energy. Regardless of whether it is in the form of electricity or from burning fuel. So it is actually very related, and much more useful than a measurement of volume I’d argue. The measurement is of course done in m³, but then a conversion factor based on several factors is used to convert to an actually useful unit.
A m³ of gas really could be anything depending on pressure, temperature and constituents.
Yeah, even firewood can be (and not uncommonly is) measured in kWh
(Brace yourself for Much 'Merica) Several gas utilities I’ve had in the USA measure natural gas CCF, which is 100 cubic feet (at some standard temperature/pressure), which happens to be almost exactly the same as a Therm, or 100,000 BTU.
My meter measures it in m3 and my supplier, knowing the exact caloric value of the product they’re selling, tells me in kWh on my bill.
edit: m3 of course not 2 lol
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50kWh and closer to 90kWh on days like this. It’s a log cabin and I’m keeping my root cellar and insulated shed above freezing aswell. Even running a 1kW heater all day would result in a consumption more than 21kWh and that wouldn’t keep any house warm.
A tiny heater running all day would do that.
1kw is a small heater. 0.8kw is a tiny one. 0.8x24 is 19.2. Assuming they have other basic appliances, that’s already more than enough to account for their usage.
I’ve got a small 1200w heater that kicks on in the morning to bring the living room space up to 69. I live in a 40 year old house that’s insulated fairly well (I just had the attic redone last year to r-49) and it’s 45f outside right now. That little heater has used 6kWh since kicking on this morning getting the house up from 63f to the near 69 it is now.
On a day below freezing that heater will got for a lot longer through the day to keep temps up.
Space heaters are the way to go.
It’s the difference between paying $70 and $5 more per month.
Space heaters are one of the most expensive methods. Check the power consumption, they are hungry things.
My electric bill says otherwise.
As always, I encourage people to see for themselves rather than trusting strangers on the internet.
The only time space heaters work well is when you avoid heating the whole house, and instead heat only a room
No shit.
You don’t exactly understand heat pumps, do you?
A space heater has an efficiency of close to 100%, heat pumps have at worst 100% and at best somewhere between 300 and 500%. Granted, in -35C environments, it’s probably very close to 100%, but that’s the absolute worst case, and an anomaly even in Finland.
What are you smoking? Space heaters gulp down electricity with the smallest ones running at hundreds of watts and standard ones around 1-2 kilowatts. The only ways a space heater is more efficient is if either you’re spending a shitton of energy heating rooms you aren’t in or if your homes heating system is in bad need of repair/replacement
Well, my electric bill went up a negligible amount and I keep the space heater running pretty much all the time.
Maybe you bought a shitty one or you’re getting a shitty deal for your electricity.
All space heaters operate at the same efficiency since they convert electricity to heat via resistance. You may have a small one and low electricity rates in your area to see a negligible change. Or maybe other uses went down and masked the increase from the space heater usage.
Almost. Some are better at heating people, others are better at heating air
Bruh I don’t think you understand how electricity consumption works.
A space heater will pull a given wattage, say 1000 watts for a pretty common one. Electric heaters are 100% efficient meaning 100% of the energy going in is converted to heat, so running that 1000 watt space heater for 1 hour will consume 1000 watt-hours (or 1 kilowatt hour) and heat the space by exactly 1000 watts or 1 kilowatt (kilo meaning thousand)
Plugging this into a electric bill calculator, at a common $0.15/kWh running that 1000 watt space heater 24/7 will cost about $100 per month
If your space heater is so insanely awesome, please do tell me, what’s your electric rate and the wattage of the heater?
Bruh, I don’t think you understand that heating a room is cheaper than heating your whole house. If I ran my space heater 24/7, I’d be sweating all day. If I run my central heater 24/7, my house barely reaches the temperature my room does before I turn my space heater off.
My electric bill is ~$160 when running the central heater. It’s ~$80 when I run my space heater.
As always, I encourage people to see for themselves rather than trusting strangers on the internet.
Experience is better than theory, every time. I feel sorry for the people who will avoid saving money because of comments like yours.
To quote my earlier comment with emphasis this time:
So you’ve already agreed with my original point, because you reduced power consumption by turning your HVAC down and using a space heater to heat just the room you’re in. Running a 4 kilowatt central heater will use more electricity as it runs than a 1 kilowatt space heater. But a 1 kilowatt space heater is still pulling down a kilowatt to run (which is a lot!)
YOU CAN LITERALLY CALCULATE THIS! Watts consumed by the heating source multiplied by number of hours per month it runs gives you the watt hours for power consumption, bigger number means bigger bill. In fact it’s important to calculate it first because electric bills will naturally fluctuate and be difficult to identify the changes in consumption due to being an aggregate of everything in your home combined with outside temperature fluctuations.
Outer walls in new homes in the Nordic countries are often 25-30 inches thick filled with insulation. They will keep out some cold (and some heat).
Heat pumps aren’t designed to function in this low of temperature. The problem is they need a real heater instead of a heat exchanger.
This is such an outdated information. Modern heatpumps work just fine even in temperatures of -20C and below. Ofcourse the efficiency gets worse the colder it is but even at worst it’s still 100% efficient. On a typical year there’s only a handful of really cold days. It doesn’t make sense not to get a heatpump just because it’s inefficient for few days. It’s not like it stops heating or something. It just effectively turns into electric radiator which is what my house was heated with before I got the heatpump anyways.
This is true only if you have a heat pump with electric/resistive backup heat. But for some reason, it’s pretty easy to buy one in the US that doesn’t. (Which is where I assume that poster is, because most anti-heat-pump sentiment seems to come from here.)
Not quite, in my experience on really cold days my heat pump struggles to keep up. This is expecially true when the outside unit is frosting up. The unit has to reverse and pump heat out of the house.
That’s one of the reasons i run my wood pellet stove on those days. The secondary source of heat takes the load off the heat pump.
Sure, but as I said it’s just a handfull of days in a year. If the heatpump alone struggles to keep my house warm I can just switch on one or two electric radiators.
In an area that gets very cold, a geothermal heat pump (which uses the ground rather than the air for heat exchange) would work better than an air-source heat pump. More expensive to install though, and you need a good amount of land
It’s basically what modern homes should have built below them. Then it doesn’t need extra space. Wonder if it’s already enough to put some pipes a meter below the basement?
Most heat pumps will use the aux coils to defrost. It’s also ok for the heat pump to literally run 24/7 if it needs to. A lot of people freak out when the heat pump runs all day and blows “cool” 80F at from the vents, but it’s still working as intended. Though I totally get how that can make a place feel “drafty” without some backup running
It’s true they’re at worst 100% efficient, but they’re also typically sized lower than resistive electric heaters in terms of input power. In the US, a residential heat pump likely draws about 4kW, whereas resistive heat strips or baseboard heating could be multiples of that. As an air source heat pump’s output drops on very cold days, a unit rated for e.g. 48000BTU/hr at 47°f might produce only half of that at 5°f/-15c. A “good” unit here would produce perhaps 75%. The way we do HVAC sizing, unless you radically oversized the system for most weather (including air conditioning) you’ll need a backup source of heat on the coldest days.
Code (law specifying how much heating / cooling capacity is required in normal worst-case weather conditions) where I live would require me to use about 2x the normal sizing to achieve pure heat pump heating at the required design temperature (around 5f/-15c). That means at the peak of summer (about 100f/38c) the unit would be operating at less than half of its full cooling capacity.
Apologies for weird units; I live in MAGAland.
They work, but efficiency is near 1:1 when it’s that cold so there’s no cost advantage over a space heater.
It’s non-sensical to base the cost effectiveness of a heat pump on the handful of really cold days when it’s no more efficient than electric resistive heating. You have to take into account the entire heating season. Electric resistive heating is allways 100% efficient. Air sourced heat pump is 100% efficient in the worst possible conditions. In normal conditions it’s from 300% to 500% efficient. While your 650 watt space heater puts out heat at the constant rate of 650 watts, a heat pump outputs 3000 watts worth of heat while using that same 650 watts of energy.
I live in a very cold part of the world where the temps can easily exceed your -20C for night times for several weeks at a time. And even as the daily high for a week stretch or two over a winter. And while I could have purchased a heat pump that would work to that low of a temperature, it would have cost over twice the price. Going from $5000US installed to over $10,000US for just the heat pump. And that included the rebate incentives.
My heat pump is set to set to cut out and switch to LP heat at -10C because it becomes cheaper to run an LP furnace at that point - cost of electricity = 6.5 cents per kilowatt hour vs $1.75US gallon LP. The loss of efficiency matters to my pocket book. And I chose my particular heat pump with my advice of my Daughter who has a PhD in ME and works as a research engineer for a non-profit studying HVAC systems and the efficiencies of the technology used in them. And she won’t install a heat pump in her house because for where she lives, they literally do not make financial sense. There is zero savings to be had with switching from natural gas heat to electric.
So installing a heat pump is not a universal no brainer. You still need to to the math to see if it pays.
Yeah obviously it’s a whole different game when you live in a place like that. That’s just quite rare usecase. The vast majority of people who keep repeating the “heatpumps don’t work in cold climates” lives in a climate much warmer than I do. Even mine struggles on the really cold days we get few times a year but that’s fine because it gets the job done flawlessly for the remaining 350 days.
My issue with these arguments is the blanket statements that get made. Both arguments on this particular subject can both be true at the same time. And until you do the math for your specific situation, you can’t tell if it pays until you know the answer
Now, I believe it works out for you just as it does for me. But I had to the math to figure it out to know for sure. Most people who argue over this subject have never done the math.
If your intention is to heat or cool air using as little electricity as possible, a basic heat pump split air conditioning unit is going to be more than adequate for 90% of people. If you live in a place like Yakutsk, then yeah, you probably need to look into something else, but for the vast majority of people it’s going to be just fine. A general recommendation doesn’t mean it’s the best choice for literally every single person.
But it very often catches many who simply take it as an irrefutable truth.
As I gave as an example, my one Daughter who is recognized by her peers as an expert in this field, and is all about improved efficiency and renewable energy, did the math and found that it doesn’t work for her. And it’s not because she lives in a terrible climate - it’s warmer and varies less than where I live by a noticeable amount. It’s because when you compare total costs, over the life span of a heat pump, she would end up paying extra to have one verses a simple natural gas furnace. It would be even sillier for my neighbor who is a logger. He uses 100% wood heat. Because he can literally harvest, process, and store enough firewood for several years in one afternoon. Anything else is far more expensive. But the math says it works for me.
You can’t make general statements about 90% of all people until everyone does the math. This is just one of the field studies my Daughter is doing. Trying to collect enough real time data on real homes and families and doing the math to help pinpoint locations where it makes sense and where it does not make sense at this time. It does not always workout like you and I might think it would.
In very cold climates, having a hybrid system like the one you’re describing is that universal no brainer in my opinion. Especially since most cold regions also typically have really long transitional periods where your heat pump is most efficient and pays itself off fastest. Combining that with turning it off during harsh winter weeks gives you the best of both worlds.
It’s not even a no brainer even then. You absolutely need to actually do the math for your particular situation to make that determination. For me it works out. For my neighbor down the road who is a logger, it does not. He can harvest, process, and store 2 years worth of firewood in a mere handful of hours. Any other heat source makes little sense for him.
You really, really, really need to do the math!
I am also an engineer and used to have LP backup heat and the only way the LP is cheaper per BTU is if you rapidly deprecate the heat pump asset.
A gallon of propane has 91,000 BTU, and a kWh of electricity has 3400 BTU. 91k/3.4k ~ 26kWh x 0.065 ~ $1.73 for electricity equivalent at 1.0 coefficient of performance. But your COP is likely around 2-3, so the heat pump will be at least 2x cheaper than the LP. It would take like 6000 hours of operation to break even on the bigger heat pump, and that’s ignoring the cost and maintenance of the propane furnace
There are heat pumps that exchange heat with the ground. Those can function well in more extreme temperatures. Also you could/should have alternative heating methods for extreme situations even if they are much more inneficient
In colder areas like that the heat pumps are usually ground source so the ambient air temperature doesn’t change the performance much.
Have you actually priced such systems and the payback time vs heat pumps vs petroleum sourced heat?
I know one person who chose a mix of ground heat pump, LP, and wood heat. He told me that it only had a reasonable payback was because he was building a new home and the extra cost could be tagged to the total build cost. Making it cheaper than a retro fit. He said it added another $25,000 to the cost of his new home. But in fairness, he does enjoy it.
I only do the refrigeration side of things and I don’t do residential stuff so I’m not sure on exact pricing. Pricing will also vary greatly depending on the exact area. For example in my area we have a high enough ground water level that open loop geothermal is easy and that is the cheapest/easiest method of geothermal. The other types will also vary in cost depending on soil type and moisture content because that will partially dictate how big of a ground loop you need. The amount of area you have for a ground loop will also be a big factor because if you don’t have enough yard area for a horizontal loop then you need to use a vertical loop which can be heniously expensive.
As far as payback goes they are far more expensive to install regardless of the type but the ground loop (assuming closed loop system) can easily last over 50 years and that is the most expensive part of the whole system by a large margin. Out of the $25,000 you mentioned I would bet that about $20,000 of that was just for the ground loop. The rest of the system is going to be more durable as well due to not being outdoors. The expected lifespan of the other components is 20 years and they can easily last far longer than that. So the energy savings is only part of the cost savings. The other part is that geothermal heat pumps need practically no maintenance and break down far more rarely than any other conventional heating or cooling solution. With how long they last and how durable they are a geothermal heat pump can probably pay itself off just with avoided service calls.
The biggest issue is if you don’t have the money to buy it, it matters very little about the efficiency and how long it lasts. You still need to pay for it. He could justify the expense because we are a very rural area and land is cheap and tagging it to a new build brings down the interest costs. This is often makes geo-thermal a non-starter for most - as you point out. He even admits he wouldn’t have done it under any other circumstance.