The heat pump I have installed reaches 1:1 at -20C, i.e. at that point there's no gain. But a) it rarely gets that cold around here, and at -10C it works fine - there was a dramatic (seriously dramatic) drop in amount of electricity I used during winter compared to before installation, and b) My heat pump was installed in 2010, since then they've only got more efficient and 1:1 is somewhere around -30C (or was, a couple of years ago when I last checked).
And what it does when it's really cold _and_ somewhat humid outside is that it detects when frost appear on the outside element, at that point it reverses the flow and uses the heat from inside to defrost the outside element. As far as I know it does not include any actual resistive heater for this (though I won't bet my life on that statement). It's been working very reliably all these years (except for a leak in the cooling fluid which appeared relatively soon after installation, promptly fixed by the provider). I have to get it cleaned now and then to keep up the efficiency. It's in every other respect completely without hassle.
EditAdd: The Japanese heat pumps sold in the coldest areas are "Nordic" models. They are extremely efficient. But in Japan, where they're made, you can't get them. Or at least, we could only find less efficient models. But I haven't been to Hokkaido yet, I'll have a look in the stores there to see if they have them there.
> at -10C it works fine - there was a dramatic (seriously dramatic) drop in amount of electricity I used during winter compared to before installation
Were you heating with electricity before? In that case you're sure so see improvement since resistive heating is always 1:1 while your heatpump is 1:1 in some of the worst cases.
Yes it was mostly heating with electricity, though I used a wood stove as well, but that's difficult to use efficiently - so it didn't help as much as I thought it would (w.r.t. saving electricity). No gas or oil. The only change was to install the heat pump, and boom - electricity usage way down. Now the biggest user is hot water (hot water tank for showers and washing). I save money by showering at the gym..
I still have the electric heaters installed in my living room - they haven't been used a single time since 2010. As they're permanent installations I haven't got them removed, or I would have.
To be clear: "zero heat gain" isn't the right threshold to think about unless your house is a closed thermodynamic system. Real houses lose heat in proportion to the temperature delta between inside and outside air. So what you really want to know is the temperature at which the heat pump is no longer capable of maintaining that delta. That's a whole lot higher than -20C.
FWIW: we installed a heat pump recently here in Portland, and conveniently had a once-in-a-decade cold snap (17-20F for 3 days -- the PNW isn't that cold) in its second month. The system was just-barely-heat-flow-positive. A six hour power outage dropped the house temperature to ~64F, and it took a good 30 hours to get back to the 69F set point of the thermostat.
So... on the whole we're pleased and the system did just fine in extremis. But no way would it handle -20C/-4F.
That's not a flaw in heat pumps, that's just the sizing of the system.
A good designer will not oversize HVAC for edge cases like a once-a-decade weather system. You will size it to meet typical conditions, saving money and increasing efficiency by having a 4 ton heat pump vs 6.
For heating conditions, the typical workaround to meet demand in edge case extreme or long term cold is to add resistive heat pumps, which are much cheaper than upsizing the whole system. Though they are less efficient and therefore cost more to operate, they will only be used a few days a year when the heat pump loses ground.
I have a 60kBtu/h ground-source heat pump backed up by 7kW heat strips that replaced a 110kBtu/h gas furnace. The heat pump meets our needs for probably 51 weeks a year. Typically we will have the strips kick on during a few days in February. But it saves us a ton of money not having to have a second heat pump or larger ground loop system.
This is extremely dependent on the efficiency of your system and how well it is designed. A 15 SEER heat pump can't compare to a 21 SEER (all else equal).
There are heat pumps that do well below freezing, they're just top of the line and so more expensive.
Air-water heat pump provides heating for our house (170 m2, Estonia, well insulated) all year round without engaging support electric heaters. In fact, breaker for support heater is always off. Temperature went to -22C previous winter for couple of days, heat pump was able to handle it. Average winter temperature is about -4C.
I'm in the Portland area and got a heat pump installed in 2021.
I overbought for sure, as I got a hybrid system that has a gas furnace backup. I've never needed it, but I've had a couple times where I wanted it and it was nice to have. If I switch it from "Heat" to "Emergency Heat", then it overrides the automatic determination of which heat source to use and just uses gas.
I didn't lose power during that cold snap, but if I did, it would have probably brought the temp back up in under 4 hours.
GP's "zero gain" was a statement about efficiency, not heat loss. ("Zero gain in efficiency as compared to resistive heating" rather than "zero gain in net BTUs inside the house".)
This and other comments here are very useful for me. Been thinking of getting a heat pump for the areas of the house that aren't reached by the pellet stove. It regularly gets to -20C here but not usually for very long so I think we'd be fine. Also we could use it for cooling for the few weeks a year when it's 30C+.
Here we ofter have summer temps around +30C and winter -20C, in both I am very happy to have our heat pump. Our unit is operational down to -25C but for the handful of weeks where it does get that low we do run the gas furnace a little just to top up.
We installed three mini splits in total for a ~2k sq ft 1800s draughty home. Before we had them our central air gas furnace, which is ~20 years old, would burn through upwards of $600 a month of gas in winter. With heat pumps we pay $180 a month equalized and we run heat or cool all year except for maybe a month in spring and fall where it's perfect 22c outside.
Without this magical tech we'd be broke or cold in the winter and uncomfortable all summer.
Is that "no gain" in terms of energy (i.e. heat energy out = electricity in), or financial (i.e. cost of electricity consumed by heat pump = cost of equivalent gas-fired system)?
EDIT: or is it "well-to-wheels" style energy (i.e. primary energy consumed by heat pump = primary energy consumed by gas boiler), or is it CO2 (same emissions)
With a 1:1 ratio it's heat energy out = electricity in, minus a small amount of efficiency loss (any heat produced on an external heater)
As to cost wise it depends on the cost per kWh of your electricity vs gas. In the UK gas is far cheaper per kWh.
CO2 wise it depends on the CO2 intensity of your electric source vs a local gas burner.
However that only applies when it's -20C. When it's a more reasonable like now at 7AM in Chicago when it's 2 degrees C, you're generating something like 2.5kWh of heat for every 1kWh of electricity. That may not be financially beneficial if your gas is 5c/kWh and electricity is 30c/kWh, that depends on your various deals.
For me in the UK, my external oil boiler this winter has cost about 10p/kWh. My electricity is 21p/kWh. A heat pump I looked at was a 3.84 ratio, so if that ratio held down as far as typical winter temperatures of 6C (it's currently 11C), that would be 5.5p/kWh, and obviously far less CO2 per unit of heat.
The only heating around here these days is electrical (edit: except for wood stoves, which are usually allowed). Oil isn't allowed, and gas heating doesn't exist. So yes, "no gain" means that the heat output is equivalent to the electricity input (at the low turning point, which is around -20C for my pump - I should qualify that though, it used to be when it was new, but the tech who checked my pump a couple of years ago said it had lost some of its efficiency due to various things including some difficult to remove grime inside, but there still was no point in actually replacing it).
Of course, there's also the installation costs of a heat pump. But it did pay for itself in a reasonably short time. If it hadn't been that efficient it wouldn't have - first, there's the actual price, which is not as much these days as it used to be, but then there's the actual installation by a pro, and I believe that part has only gone up since then.
This is a good point. And I'd imagine most people when talking anecdotally on their own experience are comparing based on cost. And of course costs will vary.
For instance we have a heat pump that we mostly use for AC. Our primary heat is a gas boiler feeding steam radiators. We'll use the heat pump in the shoulder seasons when you just want to take the chill out of a specific room, but usually nothing else heat wise.
Last winter our boiler died and we spent about a month without it. That provided me a good opportunity to do something closer to apples/apples. Despite having the cold weather rated heat pump (Mitsubishi HyperHeat2) the extra electricity consumed that month was about the same as our typical gas cost. A slight bit more actually.
But I have no idea about energy usage in an objective sense. And if I really wanted to go down this rabbit hole, we're subscribed to an energy plan that's mostly based on renewables whereas obviously 0% of our gas is the same.
I’m not fan of a heating technology that only fails when I need it most. The system can work adequately thousands of times, but I only get to freeze to death once.
Winter Storm Elliott dropped temperatures far below the average lows in places that might otherwise be well served by heat pumps. Many southern states saw -5 F and it got considerably colder elsewhere.
That’s not to say that heat pumps can’t play a role in HVAC systems, but they must have a backup.
You always need a backup heat source in cold climates. Even if you have typical heating like baseboards of central gas furnace, they can and do fail and for that reason you need backup. Heat pumps are no different, but their efficiency drop off isn't a "failure", it's just a limitation. Being a predictable limitation you can plan for it, and be sure your backup source does not rely on electricity because that always goes out in a storm.
I have a heat pump and I live in Canada where it’s not uncommon to see -40 degree temperatures in winter. The system has a high efficiency gas furnace as the backup (auxiliary) heat source. So far this winter the heat pump has been doing the bulk of the work. Only when the temperature starts to drop and the heat pump can’t keep up does the gas furnace kick in. The system works pretty well.
I just wish the thermostat let me customize the threshold a bit. I don’t like having the heat pump go to maximum load before it lets the furnace come on. Ideally the system would know the current prices of both gas and electricity and run whatever is cheaper, given the indoor and outdoor temperatures.
We converted about 6.5k sqft of living and work space to heat pumps. Fujitsu. Some commercial products due to sizing. Can generally recommend. Controlling heat pump head units is a little different from typical HVAC. Good systems, very reliable, strong track record in residential and commercial space. New units have good tech.
My 2010 heat pump is a Panasonic model. Panasonic, Mitsubishi, Fuji, Toshiba and others have Nordic-specific models. Several of these reach 1:1 at -30C, and some of them are reasonably efficient even at -25C, which is super impressive when compared to my 2010 model. Obviously they will need regular maintenance, keeping the radiator clean etc, and these are very thin and sensitive so you may have to get a professional to do it.
Edit: Looking at the specs for current Mitsubishi models, they are pretty decent (as in: Getting more out than you put in, and useful effect too) at -25C, reaches 1:1 at -30, or, for some, even colder. At optimal conditions you get 4.4 to 5.5 times as much out as you put in, depending on model and temperature.
I think the single biggest mistake is differentiating HVAC from heatpumps. The second is not insulating
In the UK most newer offices use aircon to provide both heating and cooling. Its cheaper to put in, requires less maintenance and regulatory oversight.
However the biggest issue is that for any of your heating/cooling systems to work cheaply, you need insulation, and enough of it to do what you need. That means insulating floors, ceilings and walls. Moreover, having a bunch of thermal mass makes stuff a lot more comfortable.
My house is a 1930s semi-detached house. Think harry potter, english suburbia, and you'll get a good idea. It was designed to have an open fire in each room. This means that it has an airbrick in each room, plus a suspended wooden floor, supplied with, you guessed it, a fucktonne of air bricks. This means in its natural state, its windier than an open barn.
This means that with a 30kw boiler (8.4 tons or 100K BTU) working flat out for hours could get the house to about 19c (~66f) at best. Not only that but condensation clung to the walls, meaning a fucktonne of mould.
Combine that with huge south facing windows, meant that in summer the front room hit 37c(98f) with the blinds drawn.
Insulation and new windows with decent coating means that this summer (when outside was 40c) the livingroom's max temp was 27.5c this december we used 1500kwh of gas for heating. (compared to almost triple that in the house across the road.)
Insulation and air control are absolutely key to efficient heating and cooling, regardless of where you live. We built a stand alone guest house a few years ago. Insulated the entire envelope with closed cell foam to R25 in the walls and R60 in the ceiling. That means it loses or gains very little heat, but also means it exchanges very little air with the outside. It's heated with an 18,000 BTU air source heat pump, although for temps above 0C, just the heat of occupants does the job. To keep it dry and maintain fresh air, it has an outside air circulating system fitted with a heat exchanger. Highly efficient and comfortable down to -20C outdoor temps. Needs supplemental resistance heat when the temps are below that, but that's at most two to three weeks a year here in the upper Midwest. Solar panels make the whole thing carbon neutral in operation, averaged over the year.
Unfortunately, retrofitting existing housing that was not designed to be tight to this level of insulation and air infiltration is enormously expensive, if possible at all. We're getting there, one improvement at a time on our main house, but it takes a lot of check writing.
If your home is sealed tight, then you should consider either an ERV or HRV system as well, depending on the humidity of your environment.
They blow air out of your house and replace it with fresh air from outside, which a fan could do, but they include a heat (and moisture, in the case of ERVs) exchanging plenum so that you don't lose all of the energy that you put into conditioning the air in your house.
They're a little spendy in the $1,000 range, but if your issue is the inside air is too humid and moisture is building up on the walls and windows, it's a good system to use for comfort.
You can also get a whole house humidifier / dehumidifier set for roughly the same price, but that doesn't provide fresh air for your house so I would only suggest that if your air cannot maintain the 30-50% humidity levels that are most comfortable for you with the ERV/HRV system.
Open fireplaces suck a huge amount of air from the room. It was once explained to me that in one particular case (a specific house) the open fireplace would typically suck 150 cubic meters of air every hour, when that was replaced with a wood stove it went down to 15 cubic meters/hour. So, an order of magnitude of difference. Those numbers shouldn't be taken as accurate of course, but at least that house got much warmer simply because they didn't have all that air sucked in from outside all winter.
Insulation in itself can cause more problems than it solves in some circumstances though, especially when it results in moisture becoming trapped within the fabric of the building.
Cavity wall insulation is one such example where there was a mad splurge of works being done poorly and where inappropriate, the inevitable result being further works required to remove it and make good the damage caused.
Insulate Britain's dream come true would be much more of the same.
> The load also depends on unique characteristics of the home like the amount of insulation or the type of windows and doors. A home built in 1850 with no insulation requires more energy than a brand new home. The load is just a technical way to describe and measure all of this.
No kidding. The site is all about switching from carbon, which I am all for, as would anyone that cares even slightly about the planet.
BUT. If you do live in a 1850s house with no insulation, getting a heat pump is a colossal waste of money that will not do the job. No matter how many fancy biased graphs and numbers someone comes up with.
Any responsible heat pump installer will firstly look at your home to determine if a heat pump is remotely feasible. Unfortunately, in the UK, only very recent new builds can comfortably accommodate a heat pump. That or older properties that have had CONSIDERABLE insulation work done to them (and I am talking the expensive kind like internal/external wall work, not just the easy jobs like loft insulation).
Be very careful with heat pump cowboys, if you are getting quotes that don't include a site inspection, run.
Could you elaborate a bit? My parents live in a not-very-well insulated wooden house from around 1900, and use a heat pump as their primary means of heating the house. This is Scandinavia, so it might be that this house (despite not even coming close to modern insulation standards) still has better insulation than most British houses, but it would surprise me (older British houses are generally built in brick, which should provide a better base level of insulation than a wooden house, and I'd think Britain isn't warm enough that nobody would build a house without any insulation whatsoever).
Maybe I don't understand what you mean by the word "feasible" – they don't have a goal of getting their living room above 23 C at most in winter, and I guess heat pumps are insufficient in such a house if you desire ambient temperatures above that. However, while other means of heating could plausibly bring the temperatures higher, that would end up being very expensive also because of the poor insulation – it's just harder in general to heat a drafty house and keep the temperature up, and I don't see how heat pumps are a uniquely bad choice for homes like that.
Edit: This is coastal Norway, so the climate in winter is quite similar to somewhere like Edinburgh, with temperatures usually above 0 C in January. The heat pumps would probably be insufficient somewhere the temperatures regularly reach -10 or -20 C, but that's a very infrequent event both here and in the UK.
British houses generally have terrible levels of insulation and if built before roughly 1930 are likely solid walled, so have no wall cavity to insulate. There is also the issue that a lot of people live in terraces and semis and there may simply be no suitable place to install a heat pump. When I looked into it for my house a couple of years ago the fitters basically said they couldn't do it because of lack of space.
There isn't that much to elaborate on. Commercial heat pumps just aren't good for the average UK house. They would be "alright" if the costs weren't prohibitive.
I don't know the specifics of your parents. A "wooden house" with a heat pump acting as the primary heating system in a country like Norway sounds fairly bad on the surface. But I don't know the insulation specifics, nor do I know what other heating element might come at play when the heating pump fails to keep up with the heat loss. Also, what heating pump are we talking about?
As long as the heat pump was properly sized for such an uninsulated home it would still heat it more efficiently than a resistive element heater and just as completely. Of course, if saving money is what you want to do, then yes, insulate before throwing dollars at anything else.
I'd argue that insulation should be the first thing people consider unless they know their home is already well insulated. It's all very well having energy efficient heating systems but if most of the heat generated leaks straight outside then I'd question whether that's efficient overall. Particularly in smaller dwellings, you can reduce the amount of heating you require each day during winter - often to nil.
Yes, it's more efficient than resistive electric heating, but in the UK that is typically not the alternative it's being compared to. The usual existing heating system would be a gas-fired central heating boiler, and the cost of gas vs cost of electricity means that gas is still cheaper, I think.
The costs are totally prohibitive, though. We're talking tens of thousands of pounds, whatever direction you decide to take.
You could spend 10s of thousands of pounds in a "properly sized" heat pump system. Or you could spend 10s of thousands of pounds in insulating your home + a more moderate heat pump.
The key issue is despite claims that cold doesn’t affect heat pumps it absolutely does. We have an old house. When very cold the heat pump struggles to put out enough heat. It works well enough, but something to be aware off - go bigger in system than you think you need maybe
> I dont understand how heat output from a heat pump vs heat output from a gas / oil / wood burner / resistive heater are at all different.
A gas/oil/wood burner are not 100% efficient in creating heat, and release carbon into the atmosphere.
A resistive heat is at most 100% efficient: all the electrons go to making the coil glow, like old school light bulbs. So 1 kW of electricity is 1 kW of heat (which has some BTU equivalent for old fashioned folks).
A heat pump does not create heat, but moves it from one place to another with refrigerant and pumps. So 1 kW of electrical usage can move 3 kW of heat at times:
I think what the post you replied to meant is that when your home needs a 10kW-20kW heater to actually be able to heat your home, then spending tons of money on a heat pump which (for the largest models) can maybe pump out 7kW of heat (equivalent) under optimal conditions (when it's not that cold outside) then you have paid a lot of money and you're still freezing. So you may as well install something else, even a simple wood stove can provide 10kW or more, sometimes much more.
To understand the difference in a short and simplyfied way:
1. Your examples are heating up the inside air by using energy (burning fuel). Doing so will always be less than 100% efficient, some heating technologies are as little as 10-20% efficient (energy per kWh)
2. Heatpumps are instead using energy to do heat transfer. Moving heat from the outside to the inside.
The latter is way more efficient, with easily 300-400% efficiency. But obviously the colder it gets outside, the less heat is in the air to extract and the efficiency goes down.
Maybe they're referring to cases where the heat pump can't supply heat faster than what the building is losing through the uninsulated walls. In such cases, you must first move out of the holey tent before installing a heat pump.
The $/capacity may be quite different. The capacity of burner systems is generally cheap, so you oversize them and if you need more heat, you just burn more fuel. The capacity of a heat pump is relatively expensive, so you size it up to something reasonable, and in an unusually cold day you may hit the limits of how much joules you can get out of it.
Also, the $/fuel is different - if one system gets three times more joules from the same fuel, it doesn't mean it's more efficient as the other system may be using four times cheaper fuel; so a 300%-efficient heat pump is more efficient than a resistive heater but may be less efficient than a furnace burning cheap fuel.
Heat pumps take much longer to heat the system, to get it to the desired temperature. Combine that with a property that is not insulated to very high standard, and you get a heating system that is incapable of keeping you warm.
Of course, you could throw more money at it. But it won't be cheap, and you won't see a return on your investment any time soon.
It's not different but the amount of heat that each system can be generated is different. And when it's cold (i.e. when you need the extra heat to be compensate for your draft home) your heat pump is going to struggle most.
+1 to this. I had a hpwh installed for my radiant system and after paying >7k to get it up and running, I learned that this model is entirely unsuited to that setup and Rheem refuses to accept a return.
If anyone wants a barely used 120 volt hpwh in the bay area, get in touch.
There is no lie / part skipped, what that number is meant to tell you is that it reaches its 1:1 point there, so it "works", with diminishing returns, down to that point. Which is where it's as "efficient" (to put it that way) as a resistive heater.
Obviously you need to take that into account - is the amount of heat you get out of it sufficient for nominal winter temperatures, at its coldest, for where you live? (geographic location and building conditions). As for myself, I have a backup in my wood stove, but I only need it under special circumstances (like last week when it was particularly cold and no electricity for parts of two whole days because I had electricians doing major rewiring in my home).
If you get to -20C a couple of times a year but normally it's -5, it doesn't matter that it's inefficient for 2 or 3 days a year, as it's very efficient for 360 days a year
The biggest issue with mass-scale installation of heat pumps is non-linear load on grid in cold weather. Failing efficiency and ultimately automatic switch to resistive heating causes electricity consumption spike, together with other accidents caused by the weather (be it reduced generation or grid damage) it can cause brownouts or full-blown blackouts. In other words, people can lose heating when they need it most.
Any programs which promote heat pump installations above a certain scale must either include huge investments into grid robustness or mandate that all heat pump installation must include fuel-based backup heating sufficient for a week or two.
> Any programs which promote heat pump installations above a certain scale must either include huge investments into grid robustness or mandate that all heat pump installation must include fuel-based backup heating sufficient for a week or two.
That's a little extreme. You also need to consider your failure modes. I live in texas where a bunch of people died due to an extreme freeze and a very poorly regulated grid. When that happened, it wasn't just electric that was lost, but a big problem was natural gas wells and pipes freezing up too.
The cost to install and maintain both systems would be an automatic deal breaker for many people. I don't think you need total redundancy, but having some is good. For example, I went and bought a "buddy heater" after that freeze. It runs off of a 5lbs canister of propane and has an automatic Carbon Monoxide cutoff. It gets toasty. It won't last forever, but it's a good emergency backup.
One thing I think everyone needs: An emergency radio with crank power. When the grid goes down, so does internet and cell towers. The only way we got news was via radio.
This is why the technology is best combined with geothermal concepts. You only have to go a few feet deep to get warmth and that solves basically every problem a heat pump has.
Only a few feet deep? Maybe in select areas, but you generally have to go a lot deeper than that. It's been my understanding that the steep cost of geothermal involves the drilling. As much as $80K just to install a decent system, from what I've heard.
The US average cost of electricity is 16 cents / kwh [1]
The US average cost of Natural Gas is $10.84 / thousand cubic feet [2]
A thousand cubic feet of natural gas contains around 300 kwh of energy [3]
So natural gas is around 4 cents per kwh. Gas furnaces are extremely efficient, buts lets round up to 5 cents/kwh to be conservative.
So a heat pump needs to maintain a COP of 3 just to be in the same ballpark as natgas in terms of cost, and closer to a COP of 4 to be cheaper. Heat pumps "work" down to -20F or so, but the efficiency severely degrades. Heat pumps as a sole heat source are not cost competitive in cold climates.
I have a heat pump in New England, and it is wonderful for 3 seasons of the year. I think all new construction should have one. But the cost to heat during winter is ridiculous. I am very glad I had an auxiliary natgas heater put in.
In Eastern MA electric is 26 kwh, and $15.00 per thousand cubic feet as per January 1st.
Most natural gas furnaces are between 80-90% efficient, but to get above 80% you need to have a high power electric fan. Which would put them roughly at 6 cents per kwh or (0.0625 for 80%).
At COP of 3, that would mean 8.66cents per kwh, and a COP of 4 would be 6.5. Which would roughly be breaking even compared to 80% efficient furnace.
One note on energy in nat gas: that assumes 100% efficient gas furnace. Cheaper furnaces are ~80% efficiency. Really good furnaces are ~95% efficiency.
Adding natural gas infrastructure to a building that does not currently have any is extremely expensive, even if the natgas furnaces aren't particularly expensive themselves. I agree it's cheaper if you have it now, but that assumes you already have a gas furnace.
I think the fear for most people is that natural gas can easily become substantially more expensive. European natural gas pricing is currently ~$20/mcf, and spiked to ~$80/mcf for some time. Natural gas pricing limits you to a single source for power... whereas power inherently has many sources it can come from. If natural gas becomes more expensive... you're stuck paying more with the furnace. With heat pumps, there's options available to alleviate pricing either for producers or for consumers (namely, solar for consumers).
Also, importantly on the COP point: you need to talk about the area under the curve in terms of cost. Although it may be more expensive per unit of heat when COP drops below ~3, you have to think about it in terms of overall cost. A furnace will be the same efficiency if it's -50F or if it's 50F outside (for the most part...). So for the periods when it's mild, but heating is still required, the heat pump is an obvious winner. I suspect that the math works out in favor of heat pumps, even with reduced efficiency during winter, for many climates. The only thing is that you'll get a much more peaky power bill. Obviously there's exceptions, but there's vast swaths of the world where a heat pump is going to make a ton of sense.
The full cost of fracked methane gas is not actually included in the price.
I'm not just talking about the environmental cost: gas consumption and production is subsidized by tax dollars, and the health costs are poorly quantified but my understanding is a growing body of evidence links gas usage in the home to childhood asthma and other chronic health issues.
The asthma issue is with gas stoves. It is irrelevant with respect to a proper gas furnace. None of the exhaust from a modern furnace enters the home air supply.
By the way, if you are going to consider environmental costs for gas you should also consider those costs for electric.
- install is important, many installs done get adequate ventilation- so cold air collects near unit.
- high ceilings can be an issue, evaluate fans to bring heat down
- gas is amazing for heating in radiant heat. We really like our radiant heat experience- global warmth and good volume
- I’m not sure if tech term, but heat volume can be an issue. We are in a 100+ year old house. The heat pump in very cold weather seems able to generate heat, but no where near quantity that gas system did if you just cranked it
- we are getting hit with tier three electric rates - switched dryer to electric etc - costs get tough!
Also this whole conversation is specifically about air source pumps. Geothermal are immune to air temperature fluctuations with the tradeoff being higher installation cost.
If you use geo thermal in combo with heat pump, efficiency is even higher and you are not afraid even -40 -50c , you still save money. NY state will ban oil burners from 2025 for the new construction.
Geo thermal is super easy just put few pipes under the ground and save money.
One variation of putting a coolant loop into the ground is to just cut a deep narrow trench and loop the coil in it like a slinky pushed "sideways".[1][2]
Readit News
And what it does when it's really cold _and_ somewhat humid outside is that it detects when frost appear on the outside element, at that point it reverses the flow and uses the heat from inside to defrost the outside element. As far as I know it does not include any actual resistive heater for this (though I won't bet my life on that statement). It's been working very reliably all these years (except for a leak in the cooling fluid which appeared relatively soon after installation, promptly fixed by the provider). I have to get it cleaned now and then to keep up the efficiency. It's in every other respect completely without hassle.
EditAdd: The Japanese heat pumps sold in the coldest areas are "Nordic" models. They are extremely efficient. But in Japan, where they're made, you can't get them. Or at least, we could only find less efficient models. But I haven't been to Hokkaido yet, I'll have a look in the stores there to see if they have them there.
Were you heating with electricity before? In that case you're sure so see improvement since resistive heating is always 1:1 while your heatpump is 1:1 in some of the worst cases.
FWIW: we installed a heat pump recently here in Portland, and conveniently had a once-in-a-decade cold snap (17-20F for 3 days -- the PNW isn't that cold) in its second month. The system was just-barely-heat-flow-positive. A six hour power outage dropped the house temperature to ~64F, and it took a good 30 hours to get back to the 69F set point of the thermostat.
So... on the whole we're pleased and the system did just fine in extremis. But no way would it handle -20C/-4F.
A good designer will not oversize HVAC for edge cases like a once-a-decade weather system. You will size it to meet typical conditions, saving money and increasing efficiency by having a 4 ton heat pump vs 6.
For heating conditions, the typical workaround to meet demand in edge case extreme or long term cold is to add resistive heat pumps, which are much cheaper than upsizing the whole system. Though they are less efficient and therefore cost more to operate, they will only be used a few days a year when the heat pump loses ground.
I have a 60kBtu/h ground-source heat pump backed up by 7kW heat strips that replaced a 110kBtu/h gas furnace. The heat pump meets our needs for probably 51 weeks a year. Typically we will have the strips kick on during a few days in February. But it saves us a ton of money not having to have a second heat pump or larger ground loop system.
There are heat pumps that do well below freezing, they're just top of the line and so more expensive.
I overbought for sure, as I got a hybrid system that has a gas furnace backup. I've never needed it, but I've had a couple times where I wanted it and it was nice to have. If I switch it from "Heat" to "Emergency Heat", then it overrides the automatic determination of which heat source to use and just uses gas.
I didn't lose power during that cold snap, but if I did, it would have probably brought the temp back up in under 4 hours.
We installed three mini splits in total for a ~2k sq ft 1800s draughty home. Before we had them our central air gas furnace, which is ~20 years old, would burn through upwards of $600 a month of gas in winter. With heat pumps we pay $180 a month equalized and we run heat or cool all year except for maybe a month in spring and fall where it's perfect 22c outside.
Without this magical tech we'd be broke or cold in the winter and uncomfortable all summer.
EDIT: or is it "well-to-wheels" style energy (i.e. primary energy consumed by heat pump = primary energy consumed by gas boiler), or is it CO2 (same emissions)
As to cost wise it depends on the cost per kWh of your electricity vs gas. In the UK gas is far cheaper per kWh.
CO2 wise it depends on the CO2 intensity of your electric source vs a local gas burner.
However that only applies when it's -20C. When it's a more reasonable like now at 7AM in Chicago when it's 2 degrees C, you're generating something like 2.5kWh of heat for every 1kWh of electricity. That may not be financially beneficial if your gas is 5c/kWh and electricity is 30c/kWh, that depends on your various deals.
For me in the UK, my external oil boiler this winter has cost about 10p/kWh. My electricity is 21p/kWh. A heat pump I looked at was a 3.84 ratio, so if that ratio held down as far as typical winter temperatures of 6C (it's currently 11C), that would be 5.5p/kWh, and obviously far less CO2 per unit of heat.
Of course, there's also the installation costs of a heat pump. But it did pay for itself in a reasonably short time. If it hadn't been that efficient it wouldn't have - first, there's the actual price, which is not as much these days as it used to be, but then there's the actual installation by a pro, and I believe that part has only gone up since then.
For instance we have a heat pump that we mostly use for AC. Our primary heat is a gas boiler feeding steam radiators. We'll use the heat pump in the shoulder seasons when you just want to take the chill out of a specific room, but usually nothing else heat wise.
Last winter our boiler died and we spent about a month without it. That provided me a good opportunity to do something closer to apples/apples. Despite having the cold weather rated heat pump (Mitsubishi HyperHeat2) the extra electricity consumed that month was about the same as our typical gas cost. A slight bit more actually.
But I have no idea about energy usage in an objective sense. And if I really wanted to go down this rabbit hole, we're subscribed to an energy plan that's mostly based on renewables whereas obviously 0% of our gas is the same.
Winter Storm Elliott dropped temperatures far below the average lows in places that might otherwise be well served by heat pumps. Many southern states saw -5 F and it got considerably colder elsewhere.
That’s not to say that heat pumps can’t play a role in HVAC systems, but they must have a backup.
The numbers above are the 1:1 point, which doesn’t mean it stops working. It just means it’s similar efficiency to an electric heater at that point.
“Freeze to death” is an extreme exaggeration.
I just wish the thermostat let me customize the threshold a bit. I don’t like having the heat pump go to maximum load before it lets the furnace come on. Ideally the system would know the current prices of both gas and electricity and run whatever is cheaper, given the indoor and outdoor temperatures.
- Cooling operating range -22°~122° F (-30°~50° C)
- Heating operating range -22°~86° F (-30°~30° C)
Edit: Looking at the specs for current Mitsubishi models, they are pretty decent (as in: Getting more out than you put in, and useful effect too) at -25C, reaches 1:1 at -30, or, for some, even colder. At optimal conditions you get 4.4 to 5.5 times as much out as you put in, depending on model and temperature.
In the UK most newer offices use aircon to provide both heating and cooling. Its cheaper to put in, requires less maintenance and regulatory oversight.
However the biggest issue is that for any of your heating/cooling systems to work cheaply, you need insulation, and enough of it to do what you need. That means insulating floors, ceilings and walls. Moreover, having a bunch of thermal mass makes stuff a lot more comfortable.
My house is a 1930s semi-detached house. Think harry potter, english suburbia, and you'll get a good idea. It was designed to have an open fire in each room. This means that it has an airbrick in each room, plus a suspended wooden floor, supplied with, you guessed it, a fucktonne of air bricks. This means in its natural state, its windier than an open barn.
This means that with a 30kw boiler (8.4 tons or 100K BTU) working flat out for hours could get the house to about 19c (~66f) at best. Not only that but condensation clung to the walls, meaning a fucktonne of mould.
Combine that with huge south facing windows, meant that in summer the front room hit 37c(98f) with the blinds drawn.
Insulation and new windows with decent coating means that this summer (when outside was 40c) the livingroom's max temp was 27.5c this december we used 1500kwh of gas for heating. (compared to almost triple that in the house across the road.)
Unfortunately, retrofitting existing housing that was not designed to be tight to this level of insulation and air infiltration is enormously expensive, if possible at all. We're getting there, one improvement at a time on our main house, but it takes a lot of check writing.
They blow air out of your house and replace it with fresh air from outside, which a fan could do, but they include a heat (and moisture, in the case of ERVs) exchanging plenum so that you don't lose all of the energy that you put into conditioning the air in your house.
They're a little spendy in the $1,000 range, but if your issue is the inside air is too humid and moisture is building up on the walls and windows, it's a good system to use for comfort.
You can also get a whole house humidifier / dehumidifier set for roughly the same price, but that doesn't provide fresh air for your house so I would only suggest that if your air cannot maintain the 30-50% humidity levels that are most comfortable for you with the ERV/HRV system.
Cavity wall insulation is one such example where there was a mad splurge of works being done poorly and where inappropriate, the inevitable result being further works required to remove it and make good the damage caused.
Insulate Britain's dream come true would be much more of the same.
No kidding. The site is all about switching from carbon, which I am all for, as would anyone that cares even slightly about the planet.
BUT. If you do live in a 1850s house with no insulation, getting a heat pump is a colossal waste of money that will not do the job. No matter how many fancy biased graphs and numbers someone comes up with.
Any responsible heat pump installer will firstly look at your home to determine if a heat pump is remotely feasible. Unfortunately, in the UK, only very recent new builds can comfortably accommodate a heat pump. That or older properties that have had CONSIDERABLE insulation work done to them (and I am talking the expensive kind like internal/external wall work, not just the easy jobs like loft insulation).
Be very careful with heat pump cowboys, if you are getting quotes that don't include a site inspection, run.
Maybe I don't understand what you mean by the word "feasible" – they don't have a goal of getting their living room above 23 C at most in winter, and I guess heat pumps are insufficient in such a house if you desire ambient temperatures above that. However, while other means of heating could plausibly bring the temperatures higher, that would end up being very expensive also because of the poor insulation – it's just harder in general to heat a drafty house and keep the temperature up, and I don't see how heat pumps are a uniquely bad choice for homes like that.
Edit: This is coastal Norway, so the climate in winter is quite similar to somewhere like Edinburgh, with temperatures usually above 0 C in January. The heat pumps would probably be insufficient somewhere the temperatures regularly reach -10 or -20 C, but that's a very infrequent event both here and in the UK.
I don't know the specifics of your parents. A "wooden house" with a heat pump acting as the primary heating system in a country like Norway sounds fairly bad on the surface. But I don't know the insulation specifics, nor do I know what other heating element might come at play when the heating pump fails to keep up with the heat loss. Also, what heating pump are we talking about?
You could spend 10s of thousands of pounds in a "properly sized" heat pump system. Or you could spend 10s of thousands of pounds in insulating your home + a more moderate heat pump.
Heat is heat, a joule of heat output by the system is a joule of heat ... or am I missing something?
A gas/oil/wood burner are not 100% efficient in creating heat, and release carbon into the atmosphere.
A resistive heat is at most 100% efficient: all the electrons go to making the coil glow, like old school light bulbs. So 1 kW of electricity is 1 kW of heat (which has some BTU equivalent for old fashioned folks).
A heat pump does not create heat, but moves it from one place to another with refrigerant and pumps. So 1 kW of electrical usage can move 3 kW of heat at times:
* https://en.wikipedia.org/wiki/Coefficient_of_performance
* https://energyeducation.ca/encyclopedia/Coefficient_of_perfo...
So if you input 1 kW of energy, do you want 0.9 kW of heat out (carbon), 1 kW of heat out (resistive), or >2 kW of heat out?
1. Your examples are heating up the inside air by using energy (burning fuel). Doing so will always be less than 100% efficient, some heating technologies are as little as 10-20% efficient (energy per kWh)
2. Heatpumps are instead using energy to do heat transfer. Moving heat from the outside to the inside.
The latter is way more efficient, with easily 300-400% efficiency. But obviously the colder it gets outside, the less heat is in the air to extract and the efficiency goes down.
Also, the $/fuel is different - if one system gets three times more joules from the same fuel, it doesn't mean it's more efficient as the other system may be using four times cheaper fuel; so a 300%-efficient heat pump is more efficient than a resistive heater but may be less efficient than a furnace burning cheap fuel.
Of course, you could throw more money at it. But it won't be cheap, and you won't see a return on your investment any time soon.
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If anyone wants a barely used 120 volt hpwh in the bay area, get in touch.
* https://www.mitsubishielectric.ca/en/hvac/professionals/fs-s...
More advanced unit (primarily for hydronic heating) that goes down to -20F / -29C:
* https://www.spacepak.com/solstice-inverter-extreme
Obviously you need to take that into account - is the amount of heat you get out of it sufficient for nominal winter temperatures, at its coldest, for where you live? (geographic location and building conditions). As for myself, I have a backup in my wood stove, but I only need it under special circumstances (like last week when it was particularly cold and no electricity for parts of two whole days because I had electricians doing major rewiring in my home).
Any programs which promote heat pump installations above a certain scale must either include huge investments into grid robustness or mandate that all heat pump installation must include fuel-based backup heating sufficient for a week or two.
That's a little extreme. You also need to consider your failure modes. I live in texas where a bunch of people died due to an extreme freeze and a very poorly regulated grid. When that happened, it wasn't just electric that was lost, but a big problem was natural gas wells and pipes freezing up too.
The cost to install and maintain both systems would be an automatic deal breaker for many people. I don't think you need total redundancy, but having some is good. For example, I went and bought a "buddy heater" after that freeze. It runs off of a 5lbs canister of propane and has an automatic Carbon Monoxide cutoff. It gets toasty. It won't last forever, but it's a good emergency backup.
One thing I think everyone needs: An emergency radio with crank power. When the grid goes down, so does internet and cell towers. The only way we got news was via radio.
The US average cost of electricity is 16 cents / kwh [1]
The US average cost of Natural Gas is $10.84 / thousand cubic feet [2]
A thousand cubic feet of natural gas contains around 300 kwh of energy [3]
So natural gas is around 4 cents per kwh. Gas furnaces are extremely efficient, buts lets round up to 5 cents/kwh to be conservative.
So a heat pump needs to maintain a COP of 3 just to be in the same ballpark as natgas in terms of cost, and closer to a COP of 4 to be cheaper. Heat pumps "work" down to -20F or so, but the efficiency severely degrades. Heat pumps as a sole heat source are not cost competitive in cold climates.
I have a heat pump in New England, and it is wonderful for 3 seasons of the year. I think all new construction should have one. But the cost to heat during winter is ridiculous. I am very glad I had an auxiliary natgas heater put in.
[1] https://www.eia.gov/electricity/monthly/epm_table_grapher.ph...
[2] https://www.eia.gov/energyexplained/natural-gas/prices.php
[3] https://www.eia.gov/energyexplained/units-and-calculators/
Most natural gas furnaces are between 80-90% efficient, but to get above 80% you need to have a high power electric fan. Which would put them roughly at 6 cents per kwh or (0.0625 for 80%).
At COP of 3, that would mean 8.66cents per kwh, and a COP of 4 would be 6.5. Which would roughly be breaking even compared to 80% efficient furnace.
Adding natural gas infrastructure to a building that does not currently have any is extremely expensive, even if the natgas furnaces aren't particularly expensive themselves. I agree it's cheaper if you have it now, but that assumes you already have a gas furnace.
I think the fear for most people is that natural gas can easily become substantially more expensive. European natural gas pricing is currently ~$20/mcf, and spiked to ~$80/mcf for some time. Natural gas pricing limits you to a single source for power... whereas power inherently has many sources it can come from. If natural gas becomes more expensive... you're stuck paying more with the furnace. With heat pumps, there's options available to alleviate pricing either for producers or for consumers (namely, solar for consumers).
Also, importantly on the COP point: you need to talk about the area under the curve in terms of cost. Although it may be more expensive per unit of heat when COP drops below ~3, you have to think about it in terms of overall cost. A furnace will be the same efficiency if it's -50F or if it's 50F outside (for the most part...). So for the periods when it's mild, but heating is still required, the heat pump is an obvious winner. I suspect that the math works out in favor of heat pumps, even with reduced efficiency during winter, for many climates. The only thing is that you'll get a much more peaky power bill. Obviously there's exceptions, but there's vast swaths of the world where a heat pump is going to make a ton of sense.
> that assumes 100% efficient gas furnace. Cheaper furnaces are ~80% efficiency. Really good furnaces are ~95% efficiency.
>> natural gas is around 4 cents per kwh. Gas furnaces are extremely efficient, buts lets round up to 5 cents/kwh to be conservative.
> So for the periods when it's mild, but heating is still required, the heat pump is an obvious winner
>> it is wonderful for 3 seasons of the year. I think all new construction should have one. But the cost to heat during winter is ridiculous.
>> Heat pumps as a _sole_ heat source are not cost competitive in cold climates.
I'm not just talking about the environmental cost: gas consumption and production is subsidized by tax dollars, and the health costs are poorly quantified but my understanding is a growing body of evidence links gas usage in the home to childhood asthma and other chronic health issues.
By the way, if you are going to consider environmental costs for gas you should also consider those costs for electric.
- noticeably lower heat output at cold temps.
- install is important, many installs done get adequate ventilation- so cold air collects near unit.
- high ceilings can be an issue, evaluate fans to bring heat down
- gas is amazing for heating in radiant heat. We really like our radiant heat experience- global warmth and good volume
- I’m not sure if tech term, but heat volume can be an issue. We are in a 100+ year old house. The heat pump in very cold weather seems able to generate heat, but no where near quantity that gas system did if you just cranked it
- we are getting hit with tier three electric rates - switched dryer to electric etc - costs get tough!
[1] https://dandelionenergy.com/geothermal-ground-loop-frequentl...
[2] https://www.energy.gov/energysaver/geothermal-heat-pumps