Heat pumps, more than you wanted to know (2023)

by nomilk • 3 years ago

263 297 3 years ago

jakedata• 3 years ago

What I know is that due to Sunday's wet snowy weather my air-source heat pump became encased in ice on the heat exchange coils. You can't physically remove the ice without risking damage to the delicate fins, so I ran it in cooling mode for a while to warm the outdoor heat exchanger and loosen the ice.

I am a happy air-source heat pump user, especially when coupled with solar panels. However there are other issues people need to take into account, especially if it is difficult to access the device for cleaning or the owner is mobility impaired.

willvarfar3• 3 years ago

I'm a big fan of heat-pumps, and happily heat a big old farmhouse with a ground source pump through heavy long deep cold winters in scandinavia.

However, at the small cottage I have for the first time just had the external units of two air-source pumps freeze solid due to snow blowing in in the current -16c spell. The defrost ran down inside the casing and formed a big block of ice in the bottom that has now reached up to the fan blades so the pump can't turn at all.

So I'm all out of heat pumps in the cottage just when I most need them :(

This is not enough to make me give up on heat pumps, but it makes me wary to rely solely on them.

Am planning a big new build, and will of course go air source to underfloor heating, but am seriously considering a backup combo wood burner for the panic week that comes each year.

tomashubelbauer• 3 years ago

When I got an air-water heat pump for my house, the installer also put in a small electric heater that is connected to the same loop going through my radiators. It is a backup in case my heat pump broke and needed to be serviced. I wouldn't rely solely on a heat pump either. The heater takes 3x the amount of energy to produce the same amount of heat as the heat pump, but since I'll almost never use it (didn't need to turn it on yet), that is negligible and the peace of mind knowing the backup is there is well worth it.

noroot• 3 years ago

For this cold spell it's a little too late, but the solution for this to add some heat-coil/heat-wire on the bottom of the heat-pump housing that you can activate in those conditions.

The issue is that the defrost mode will defrost all the ice from the fins, but it freezes again before it can all drain through the small drain hole on the bottom of the housing. It's somewhat a known issue with air source heat pumps, sadly. I've not run into this issue myself, but on a Dutch speaking forum (tweakers) there is a long thread about this modification to "survive" the cold spells with this small modification.

You can manually attack the ice with a heating gun or hair dryer to remove it, but that's a faffy.

I think manufacturers should, and probably will, add something like this themselves in the future.

throwaw33333434• 3 years ago

I'm building a new house and I'm based in Poland. I'm going with air heat-pump* + a simplest fireplace as a backup - not connected to central heating, no electronics. On top of that 10-20kW of solar and a place for batteries. I'll install them once they get cheaper. The house is 200m^2, so I'm hoping to pull only 200 kW/month from the grid and generate rest on my own.

Also, I've been wondering how much efficiency would I get if I could put some mirror and direct the light to the unit in the winter. It could help with defrosting as well.

*I was considering horizontal heat pump, but it's not worth it. It affects vegetation and future construction.

nottorp• 3 years ago

... and your heat pump is on the ground, easily accessible.

What if you live on the Xth floor? Your gas burner is small enough to be all inside and easily serviceable when it breaks in the middle of winter (why would it even consider breaking in summer?). Where do you put the much larger heat pump and how do you reach it?

usefulcat2• 3 years ago

We have an air source heat pump with a gas fired backup ("emergency" heating, it's sometimes called in the US). Don't need to use it often but it's nice to have and only added around 10-15% to the total cost.

tiborsaas2• 3 years ago

You can have an extra heater device installed into your external unit. I'm just about to have 3 units installed and they will fit this extra module.

tiborsaas2• 3 years ago

Update: just had a call and it's a hack that voids warranty. There are units with built in heaters. Picking an AC is a nightmare with OCD :/

raugustinus• 3 years ago

Here in the Netherlands there's a huge incentive to move to heatpumps (subsidies and whatnot). I believe most of those (if not all) that are being installed have a defrosting mode which is automatically activated. I have seen mine defrosting in the last few days since it's finally below zero (celsius).

Faaak• 3 years ago

Yeah, it's really strange to have an heat pump without automatic defrost, as it's something that's really needed on cold and humid days

johnchristopher• 3 years ago

How much does it cost in the Netherlands (with incentives such as government subsidies) to install (hardware and installation) ?

ChatGTP3• 3 years ago

Do you have it undercover / out of the elements some how? Mine is under a concrete stair case and I've not had this problem, even when it's down to ~ 8c and very snowy.

hasmanean9• 3 years ago

Could that have been solved by placing a tarp over the unit beforehand?

londons_explore• 3 years ago

How much energy is 'lost' in the expansion valve in a typical heat pump?

Isn't it worth putting a turbine in there to recoup the energy released as a high pressure liquid passes through a small hole?

Even if it's only 10%, that's still 10% of the energy use of your home for a decade - surely that pays for a micro turbine (which need not be particularly complex - the same design used in those $3 light up novelty faucets would probably work.).

doublesocket• 3 years ago

There are various research projects looking at storing waste heat, often for the purpose of more efficient defrosting.

https://www.nature.com/articles/s44172-022-00018-3

Kichererbsen• 3 years ago

I worked for a chair that studied this kind of stuff - your best bet is to figure out how to reduce the temperature lift. Due to the way the Carnot equation works (at least, that's what I _think_ it's called, this is all a while ago), that really get's the heatpump efficiency singing.

reduce the heating temperature by increasing the area you're radiating from - floor heating / ceiling heating is way more efficient than radiators since you can deliver the same amount of heat at much lower temperatures to the space.

Firadeoclus• 3 years ago

Putting fans on radiators should also increase the amount of heat that can be transferred, right?

volemo• 3 years ago

For a novice to delve into heat pumps I recommend Technology Connections’ series on the topic: https://youtube.com/playlist?list=PLv0jwu7G_DFVIot1ubOZdR-KC...

drbytes• 3 years ago

That video finally convinced me to install mini splits. It has turned out to be a great choice as it has cut my propane use in half.

happytiger3• 3 years ago

My buddy just installed a dc hybrid system and it’s been pretty much amazing. He’s in a warm climate with lots of sun though, but the idea of plugging panels directly into solar panels on hot days makes so much sense.

Are you in a cold climate? My biggest concern is installing splits in very cold mountain climates (my use case).

Night_Thastus• 3 years ago

Mini splits are very cool in concept, but somewhat problematic in practice. Many are built very substandard, and within a few years getting parts or repairs is often impossible.

I wish that weren't the case.

gennarro• 3 years ago

Yes amazing suggestion. Came here to say the same.

Everyone: just watch this to start your journey.

goryramsy• 3 years ago

Technology Connections had some really good videos. I usually listen to them audio only, like a podcast, which makes for an enjoyable commute.

robinwassen2• 3 years ago

I do not understand why heat pumps are so expensive in the article.

In Sweden the hardware cost around $1k - $2.5k and installation $500 - $1000. It's not a complicated task.

Geothermal heating on the other hand cost around $15k - $20k.

Most people I know have one of these, direct electricity to heat is not really an option.

rcxdude2• 3 years ago

Heating has strong 'follow the crowd' effects: the cost of different options are heavily influenced by what's already commonly used in the local area, because the supply chain will be optimised, and local workers will be most familiar with what's most popular. Bucking the trend in any way sets you up for higher hardware costs and much higher installations and maintenance costs, even if in a different country the same option would be the most economical. (I have experienced the same pain, in a country where most heating is plumbing and radiator based, having a house set up for central air heating and wanting a replacement for the central unit, it was almost the same cost to replace that central unit as it was to rip out the whole thing and replace it with radiators, which is ridiculous on the face of it but a consequence of the supply of parts and labor for each option).

namdnay• 3 years ago

I think the costs given in the article are for a whole house (including "ducting" which is more rare in europe)

gavin_gee2• 3 years ago

i dont think so. Seattle quotes for a gas to heat pump conversion using existing ducting and refrigerant pipes was 18K.

labor costs are absurd

wil421• 3 years ago

Are you talking about mini splits being 1-1.5k?

In the US, it’s more common to have 1 or 2 large units pumping into ducts in every room of the house.

a_humean8• 3 years ago

The big cost is the upfront cost of insulation and removal the existing heating systems.

Speaking about the UK (article is mostly about he US which will have their own problems), we have very poor quality housing stock with effectively zero insulation. You hold your hand to the exterior walls of your typical 2-3 bedroom terrace house (the most common type of home in the UK) in the winter and its just ice cold. For these homes the exterior wall are just solid brick and plaster with no air gaps. Many homes still don't have double glazing and their windows bleed even more heat. These homes go cold quickly when you turn off a gas boiler, and a heat pump just cannot keep up with the heat loss.

In addition large numbers of households in the UK have migrated to "combiboilers" heating systems that dispensed with hot water tanks for on demand hot water from their gas boiler. In the process many of these properties have converted the space previously designated for hot water storage to loft extensions or other home upgrades. UK homes are pretty small, and going to a heat pump system means going back to hot water storage, which most UK homes have no space for without costly changes to the home layout/structure potentially including sacrificing parts of precious loft conversions.

Frankly we might be better off just knocking down and rebuilding some of our housing stock at higher densities such is the cost of retrofitting and our housing shortages, but there is no political appetite in the UK for any radical solutions like that.

AniseAbyss2• 3 years ago

In my country builders didn't seriously start to consider "insulation" until the 1990s.

Gas was cheap so nobody cared. Just turn up that dial!

Modern houses and apartments are marvels of engineering though.

pastage• 3 years ago

What is so special about insulation for heatpumps? You need that insulation anyways.

EDIT: ok so the best interpretation I have is that it has just been so cheap with gas that people have not bothered insulating their houses.

DrScientist3• 3 years ago

Frankly we might be better off just knocking down and rebuilding some of our housing stock at higher densities such is the cost of retrofitting and our housing shortages, but there is no political appetite in the UK for any radical solutions like that

Indeed. However a first step would be to put in decent building regs so that sub par new houses aren't being built! Still waiting for the new regs that were originally started in the planning back in 2006 or so.

michaelt6• 3 years ago

Speaking about the UK [...] we have very poor quality housing stock with effectively zero insulation.

To expand upon this, consider an urban street like this: https://maps.app.goo.gl/A4HSZ2TFiJ2PyiAZ8

Beautiful houses with period features, in a great location. Big, traditional sash windows that let in loads of light. An L-shaped layout giving lots of natural light in all rooms. High ceilings. Market price about £2 million https://www.rightmove.co.uk/properties/139018139#/?channel=R... (admittedly being in London pushes prices up a lot - but the point is, these are desirable properties)

The walls are all solid brick, no cavity and no insulation. The L shaped layout means a lot of external wall area, and the big windows don't help either. High ceilings make it even harder to heat. Many of these properties are prone to damp problems if they don't get enough fresh air circulating. You can't add external insulation without covering up the period features. Obviously you can insulate the loft and install double glazing - most of them will already have done so.

It turns out nobody wants a £2000/year heating bill - but also, nobody wants to knock down and rebuild a £2M house over a £2000/year heating bill.

throw0101d4• 3 years ago

You hold your hand to the exterior walls of your typical 2-3 bedroom terrace house (the most common type of home in the UK) in the winter and its just ice cold.

The opposite is now becoming more true: with heat waves that seem to occur more often, you want to keep the heat out and the cold in in the summer.

dkjaudyeqooe• 3 years ago

I run a building with 5 apartments with central water based wood fire heating, ie a furnace and radiators in various rooms. It's brick construction with no insulation. It's absolutely stupidly constructed.

The central heating is still there and used sometimes, but I installed mini-split reverse cycle air conditioners in each apartment and they work great, you just have to size them (power wise) correctly. They were 550-700 euros each installed. It's much much cheaper to pay for electricity than the equivalent amount of wood, even after the cost of the units. There are various additional benefits like being able to use the aircons when it's briefly cold, or you just want to warm up the space a bit. You also get cooling for no additional charge of course.

Mini split systems are not always the best solution, but they are another useful option to be weighed against larger central heat pump systems. All depends on the situation, but heat pumps are the present and future, nothing else makes sense.

nsteel2• 3 years ago

The bulk of the cost in the UK seems to be the actual unit. I don't understand why, other than boiler manufacturers trying to maintain the status quo (oversized boilers that can be badly installed by one of the many gas-safe "engineers" already out there).

The split of cavity to solid walls is pretty even in the UK. There are gov grants available for insulation, both for walls and loft. It is true that many houses have moved to a combi-boiler and lost their hot water cylinder but cylinders are smaller than they used to be and personally I would guess the number of converted lofts in these cases is relatively small.

https://www.checkatrade.com/blog/cost-guides/air-source-heat...

https://www.gov.uk/apply-great-british-insulation-scheme

The main problem with an ASHP for your typical 2-3 bedroom terrace house is there is very limited outside space to put the thing.

usefulcat2• 3 years ago

UK homes are pretty small, and going to a heat pump system means going back to hot water storage

Why not a tankless water heater? They are quite compact, and can be powered by gas or electricity. Are they just not really a thing in the UK?

NorwegianDude• 3 years ago

Good question. Seems unlikely that the prices are correct. If it is then someone has a huge incentive to import from other places. The most popular air-air heat pump in Norway with a SCOP above 5 is less than 2500 USD including installation and tax.

But, it's also a fact that the US is far behind when it comes to heat pumps and energy efficient homes. The general knowledge in the US about heat pumps is terrible.

nkurz• 3 years ago

I fear you are wrong. I'm American, and can confirm that heat pumps in the US are still very expensive upfront. There are often grant programs that can offset some of the cost, but for whatever reason they are much more expensive here than Europe.

The main issue seems to be that installation is extremely expensive. Less expensive heat pumps are now available here if you are able to do the installation yourself, but installers will only work with the expensive brands they know. They are usually overbooked, and thus have no incentive to lower their prices.

The question would be what it would take to get competition in the market at the installer level. Any idea how this was accomplished in Norway?

brabel4• 3 years ago

Are you talking about small units you put on your bedroom or whole house units?

I've just bought a big heat pump in Stockholm, this model from Nibe, which the guy installing it told me is one of the best: https://www.nibe.eu/sv-se/produkter/varmepumpar/franluftsvar...

It warms the whole house via floor heating (IIUC it's hot water circulating) and also ventilates almost all rooms (but that seems to be only for keeping the air in the house clean - it "pulls" instead of blowing warm air or something like that).

It cost me a total of 130,000SEK, which is 12,0000 USD (as I write this). Approx. half for the unit and half for installation costs. I don't have the geothermal option where I live because it's a water reserve, but that would be much more expensive, I expect at least twice as much.

I didn't buy a cheap unit, there was a cheaper model that they offered for a total cost of 80,000 SEK... but still, where could've I gotten this for 20,000 SEK :D

robinwassen2• 3 years ago

I am thinking of the more basic air/air units rather than this air/water.

One well placed air/air can reduce the need for direct electricity heating a lot, even though some might be needed to assist in a bedroom or so.

My parents installed a air/air unit in the middle of the house (180kvm) for $2.5k this summer and it keeps the whole house heated except one bedroom that needs some assistance from a radiator.

ffgjgf1• 3 years ago

Retrofitting floor heating might be very expensive though? Especially in some older houses

altacc3• 3 years ago

I have an earlier version of this and they're great, although they use the heater more than the heat pump in winter so bills are cheaper but not miraculously so. The newer versions like your have a bigger compressor, which I think gives them a substantial improvement.

The main problem I've found is now that it's getting old and having problems there's nobody in my area that knows how to maintain them, they only install and then suggest buying a new one when the old one needs new parts, which is frustrating and in line with most white goods these days. So advice for the future is that forums like byggahus.se are good for advice on trouble shooting & parts replacements once it gets old enough to have problems.

quickthrowman• 3 years ago

In Sweden the hardware cost around $1k - $2.5k and installation $500 - $1000. It's not a complicated task.

These numbers must be for an air to air mini-split unit with one air handler with nearby electricity, $500-$1000 is 4-8 hours of labor. That’s not nearly enough for an entire home.

A whole house heat pump with heat exchanger costs substantially more, both in equipment and labor.

soco2• 3 years ago

In Switzerland I was quoted about 25k for an air-water and about 10k more for geothermal. And I mean with it only the hardware and installation - as the house doesn't need piping or whatever. So for some reason you Nordics are quite privileged, and I wasn't able to find out why.

tsss• 3 years ago

If your Samsung heat pump costs 1-2k you can expect the same product from a German company to cost 7-15k for no appreciable difference. Why buy the German product then? Because the builders who install it will get a cut of course. They don't need your business and will simply refuse the job if you don't buy the most expensive materials. You can add to that cost all the subsidies of the German government, which, as everyone knows, simply increase prices when there is a supply shortage. But these subsidies are tied to other requirements to make your house more energy efficient, like installing a solar power system with batteries (30k€ easily).

Heat pumps are a gimmick for rich people that already have well insulated modern homes. For everyone else it is vastly more expensive than gas or oil and in addition, we have to pay taxes for all the subsidies going to those rich people.

_whiteCaps_• 3 years ago

If the Samsung heat pump works as well as my Samsung fridge does, I'll definitely look into a German product!

msh• 3 years ago

You are comparing prices of air2air heat pumps with air to water. The latter is much more expensive and you cannot get them for 1k$ in Sweden.

Glawen• 3 years ago

indeed, was going to say the same. It cost me around 15k€ to upgrade my house to a air 2 water heat pump in France.

time will tell if I will get a return on my investment, the big question will be how long my heat pump is going to last

altacc3• 3 years ago

Depends upon the heating system. A cheap air to air, single unit heat pump does not cost much but if you want anything more then it costs more. A lot of houses with a basic heat pump use it to reduce the amount of other heating used and pump hot air into a single area of the house, with additional electric heaters in other rooms and a water heater for hot water.

However to totally replace your entire heating needs with an all-in-one system is much more complicated than that. The heat pump I have alone in Scandinavia costs roughly $6-10k. That's powering water heating in every room plus hot water in the taps, zero additonal heating of air or water required. It's the size of bulky floor to ceiling fridge and does wonders for my electricity bill!

pjc507• 3 years ago

Could you put some capacity numbers next to those costs? My 5kW air->water system was about £15,000 installed (before government grants).

c2h5oh2• 3 years ago

I was quoted around $80k (in central EU) all in for 50KW heating unit. About a third was drilling of silly number of holes (water-water heat pump). Price didn't include updating radiators / installing underfloor heating in the house itself.

If I replaced wood pellet boiler I use right now with a heat pump I'd break even in about 20 years, which is longer than the expected service life of the pump..

nagisa3• 3 years ago

Out of curiosity, why did they think 50kW was a necessary amount of energy to heat? Is the building old and poorly insulated? An A/A+ energy class 150m² home barely needs 1/10th that amount.

If it was indeed a question of insulation or airtightness, then perhaps spending a part of that money for renovations in that area and only then a fraction of the price for a reasonably-sized heating unit might be sensible. You could also do just the renovations and thus reduce your wood pellet usage substantially as well – already a big win for the environment.

nagisa3• 3 years ago

I got “away” paying almost exactly €10k for fancier ground-source setup using a 6kW Thermia (i.e. Swedish) heat pump (itself about €6k.) IIRC there were definitely cheaper geothermal options back when I was investigating, but I got sold on the ecology aspects of that particular solution as well.

I can make some comparisons between the two too – ground-source maintains great COP even if its -20°C or less outside (as it was a couple days ago.) The incoming carrier liquid remains comfortably around 5°C, no matter the season. This also enables passive floor-based cooling. With an air-source heat-pump one would need some sort of a reversible cycle setup, I suspect, or perhaps a separate AC, which would likely bring the total cost of an air-source implementation up a little bit further.

It is also no-louder than your modern fridge. My neighbours’ air-source heat pumps’ exterior units were going at it so hard one could have been excused if they mistook there was a busy airport within an earshot. On the other hand if there's already an airport, what does it change if there’re N planes or N+1 planes in it :)

frankus4• 3 years ago

You can do radiant cooling with an air-to-water heat pump just as you can with an air-to-air or water-to-water heat pump.

The main issue is managing humidity so that the dewpoint stays below the emitter temperature.

rompic5• 3 years ago

Please note that they can also be very loud, especially the ones not built to be silent.

ChatGTP3• 3 years ago

They can also be crazy silent, I have one at my place I just installed, it's "air based" it's ridiculously quiet.

Like most machinery, if it's mounted to your wooden or steel framed house, it's going to vibrate the shit out of it most likely. I have mine on a concrete slab.

rompic5• 3 years ago

My neighbour (illegally) put it right next to our house (between the walls of his houses and ours in a very dense area which is a very bad idea) and I basically had to move out for a few month in winter because sleeping was impossible, before I was able to convince him and get it moved (which I basically paid to be able to sleep again)

2rsf2• 3 years ago

I suspect that there is something very wrong, or VERY cheap, with your heat pump. I have never heard a heat pump being VERY loud, and I have listened to a few that were more than a decade or two old.

rompic5• 3 years ago

See my comment below. The heat pump of my neighbour was perfectly within spec (Fujitsu woha080lfca).

It emitted around 69 dB (measured on our side of the property, also checked by an expert). Allowed (on the border of the property) were 35 dB (rule of thumb: you should not hear it in the surrounding soundscape; note that this is a logarithmic scale so I think it's a factor of 6 or something)

It was especially bad when it had less than 8 degree Celsius because it would defrost every 30 minutes or so.

As I wrote before: location is also an important part: his house is hard walled, ours is a prefab house built out of wood. There are only 4 Meters between our houses, it was approx. 2 meters from our wall blowing in our direction. They only thing they could have made worse is putting it in a corner.

I didn't only hear it, I felt it.

In the end I managed to convince him that I pay an acoustic expert to explain to him that 65 dB is way louder than 35 dB and that putting an acoustic hood around it does not solve the problem (approx -10 db).

hasbot• 3 years ago

Yep. It used to be only summer that I would be bombarded by noise from the neighbors HVAC equipment. Now it's all year. Winter is worse because defrosting is very noisy.

cousin_it3• 3 years ago

It's fun to think about theoretically more efficient methods of heating.

1) Heat pump - you use electricity to move heat from the outside in. It has efficiency over 100%, because you get all of the electricity's energy, plus some of the outside heat.

2) But generating electricity at the power plant uses heat in the first place, and wastes a lot of it. Let's bring the fuel to the house and make a heat-driven heat pump. This way you get 100% of the fuel's heat, plus heat from outside.

3) But this is still wasteful, because fuel burns hotter than the temperature you want in your house. So you could generate some electricity along the way, and use it to power domestic appliances. This way it will do useful work, and then 100% of it will also end up heating the house, because there's nowhere else for the energy to go.

4) And even that is still wasteful. The house is too hot in summer, and during the day, and too cold in winter, and during the night. A large enough heat reservoir, like thick walls, can smooth out this variation and give you average temperature all the time.

5) And believe it or not, even that is still wasteful. The human body produces enough heat to be warm in most temperatures, given good insulation. So we go from needing thick walls to needing thick clothes, which are much cheaper.

6) And even that is still wasteful! Because you don't need thick clothes either. So we arrive at the perfect solution for staying warm: a pill that makes your body heat up without fuss when it's cold, and lose weight along the way. Combine with clothes to taste.

everdrive• 3 years ago

So we arrive at the perfect solution for staying warm: a pill that makes your body heat up without fuss when it's cold, and lose weight along the way.

Only part of this your body doesn't automatically do on its own is the "without fuss" bit. And that part can be trained.

jamessb• 3 years ago

a pill that makes your body heat up without fuss when it's cold, and lose weight along the way.

A mitochondrial uncoupler like 2,4-Dinitrophenol will do this [1], but I don't think the risk of death is worth it.

[1] https://en.wikipedia.org/wiki/2,4-Dinitrophenol

JohnVideogames• 3 years ago

Some factors you haven't considered:

1) heat pumps make much more sense when you don't burn things to power them. Solar PV, wind, hydro etc powering heat pumps mean you turn energy that is not heat into heat 2) there's no physical reason that you can't run a heat pump in reverse to provide cooling when necessary 3) I need to heat my house along with myself! In the UK there has been a "heat the person, not the home" movement in response to high heating gas prices. Result: a plague of damp and mouldy homes

matrss3• 3 years ago

1) heat pumps make much more sense when you don't burn things to power them. Solar PV, wind, hydro etc powering heat pumps mean you turn energy that is not heat into heat

A heat pump that is entirely powered by electricity generated from natural gas is most likely still more efficient than burning that gas to directly heat a house. Obviously though, using renewables is better.

hasmanean9• 3 years ago

Another approach is to heat the interior walls and ceiling instead of heating the air.

Neglecting clothes for a few minutes, your body both radiates heat and absorbs it. When you are in thermal equilibrium you feel warm. If your walls and roof had low grade radiant heaters on them and emitted enough infrared to balance your own outgoing radiation, you’d be warm, even if the air temperature was cold and you had no clothes on.

So if you covered your ceiling with cheap thin iron sheet metal and built small induction coils behind them and heated the ceiling instantly, you could instantly feel warm in a cool room. Exit the room and you turn everything off…letting it lose its tiny amount of heat.

So proper system design could let you have low latency zone heating. Since you usually don’t use all the rooms in your house at the same time, there ought to be more than 50% efficiency in that sort of a system.

2. Our current approach of heating the whole house through forced air is much less satisfying than having a concentrated heat source (like a fireplace) that you can just walk towards and get as much heat as you want out of. Maybe psychological factors might play in…if you “could” be warm with just a little bit of effort maybe you won’t mind being colder than normal. Maybe heat gradients are better for you than uniformly high heat.

zimpenfish2• 3 years ago

heated the ceiling instantly, you could instantly feel warm in a cool room

Having lived in a place with ceiling heating, after the first couple of uses, I turned it off because it did nothing more than give me a headache.

cousin_it3• 3 years ago

Hmm, I'd expect that our bodies mostly exchange heat with their surroundings by conduction, not radiation. So a heater that warms me up by radiation feels a bit suspicious. Are you sure it'll have no negative health effects?

kseistrup2• 3 years ago

I'd prefer floor heating. Your feet will never again feel cold during the colder seasons + warm air travels upwards, thus distributing the heat to the entire room.

infecto2• 3 years ago

I am thinking this is already solved. Radiant floor heating.

shellfishgene2• 3 years ago

You can buy infrared heaters that are exacly this. They are easy to install and often look nice, like a picture or mirror. Also they of course heat the furniture and everything, too, so with the low efficiency of electric heating it's not a great option.

hasmanean9• 3 years ago

6) heated and cooled beds make sense for 8 hours a night.

CalRobert• 3 years ago

One thing to keep in mind is there are reasons to keep stuff warm, and not just your body. Condensation, etc. is a pain in wet places (Ireland for instance).

ajb• 3 years ago

Indeed, not just a pain - condensation causes mold, which can be lethal.

pjc507• 3 years ago

And even that is still wasteful! Because you don't need thick clothes either. So we arrive at the perfect solution for staying warm: a pill that makes your body heat up without fuss when it's cold, and lose weight along the way

The tech industry once again coming back to amphetamines.

pas• 3 years ago

https://en.wikipedia.org/wiki/2,4-Dinitrophenol#In_humans

... probably the food needed to keep a constant body weight would be more expensive than paying for heating

ah, I see someone already posted it https://news.ycombinator.com/item?id=38925082

gruez• 3 years ago

a pill that makes your body heat up without fuss when it's cold, and lose weight along the way

https://en.wikipedia.org/wiki/2,4-Dinitrophenol

ppsreejith3• 3 years ago

It has efficiency over 100%, because you get all of the electricity's energy, plus some of the outside heat.

To add to this, the typical efficiency is 300% or more. Since typically most of the heat comes from being "transferred" from the outside.

tootie• 3 years ago

Insulation is going to improve efficiency of any system. Generating power at grid scale is usually more efficient than what you can do at home. And you can maybe put your faith that the grid will migrate to renewables in the next few decades while upgrading homes is a lot more labor intensive.

truculent• 3 years ago

Regarding 6 - this strikes me as not being a million miles off from using radiant heating methods to warm individuals. Would be very unusual to have in a house but you sometimes see them in churches in the UK and Europe where heating the space isn’t feasible.

Regarding 4 - https://www.granddesignsmagazine.com/grand-designs-houses/gr...

jacknews• 3 years ago

It's not more than I want to know.

It seems ground-sourced is a much better idea than air-sourced, and it seems to me you could install the ground loop with/under/around the foundations for new builds.

As far as indoor distribution goes, it seems like a low-temperature hydronic system would be most efficient, and most comfortable. Or at least a hydronic (instead of refrigerant) loop to multiple chiller/heater units, which would be easier to install and change.

andruby• 3 years ago

Typically the installation cost for ground-sourced is a lot higher, especially when it's not a new build. Air-sourced is the same as regular A/C and thus about as cheap to install.

You're right that ground-sourced should have better efficiency and thus running costs, especially in winter.

bill382• 3 years ago

A few years ago, Google had an advanced research project for ground source heat pumps. They spinned it off in Dandelion energy.

frankus4• 3 years ago

Ground-source real-world cost effectiveness for residential use isn't that great (see here, although unfortunately paywalled: https://www.greenbuildingadvisor.com/article/geothermal-heat...).

The gotchas are the energy used to run the circulator for the ground loop, and the fact that over the course of a heating or cooling season the ground temperature lowers or raises, respectively, by enough that the COP isn't even much greater than an air-source system (but this would definitely vary by climate).

Coupled with the much higher installation cost, it's a bit hard to make a system pencil out for a building the size of a single-family house.

bluemax• 3 years ago

Several companies are developing thermo acoustic heatpumps that will have some advantages over regular heatpumps. They should produce less noise, don't use greenhouse gasses and work in a wider range of temperatures.

https://www.blueheartenergy.com/ https://www.equium.fr/en/home

DrScientist3• 3 years ago

Anybody got any actual experience of these yet?

hasmanean9• 3 years ago

LBNL had a solid state thermoacoustic resonator the size of a coin, which I read about but never saw it in the market. It was supposed to be able to extract heat from anywhere.

rihegher• 3 years ago

Equium is using helium, a non renewable gas. Not a greenhouse gas but not really sustainable either.

bill382• 3 years ago

They fill the core of their heat pump with helium at 30+ bars and seal it. That's all. It's not used continuously. So not a big quantity used.

rjmunro2• 3 years ago

I hate the sentence:

Heat pumps are unique in that they are a tool for fighting climate change, where we have the technology today.

No. They are not unique at all. We have electric cars, wind turbines, solar panels, hydroelectric, nuclear, recovery of methane from waste, "smart grid" technology and many many other things today. And not just "the technology", in some theoretical sense, we have all of the above actually working now.

There's also things like more efficient light bulbs and electronics that use less power when not in use that are now nearly 100% of the market. You can't buy incandescent light bulbs or TVs that use several watts of power in standby mode any more.

hasmanean9• 3 years ago

That sentence is not aimed at the consumer, but is a very efficient mechanism for capturing government subsidies.

stinos4• 3 years ago

No. They are not unique at all.

In my opinion they still are pretty unique because their efficiency is higher than 100%. Which was what I thought the sentence would continue with when I started reading it. Cannot be stressed enough. It's like magic :] Sure your LED is more efficient than your incandescent light bulb, but it still produces heat which is not intended nor really wanted. In my book there's no comparing that to a heat pump. That being said, not really a fan of such sentences either.

rjmunro2• 3 years ago

% electrical efficiency is not a useful measure. What matters is how much do I save (measured in money and/or carbon emissions etc.) compared to taking other measures, such as a more conventional heating solution, better insulation or installing solar panels.

If you measure the efficiency of solar water heating in the same way, it uses no electricity, so it's efficiency is infinite.

frankus4• 3 years ago

Space heating/cooling, along with water heating, are the overwhelming majority of household energy use. In fact, in a heating-dominated climate there isn't much of win from having efficient lights and appliances, because the space-heating system has to make up for the energy not wasted by the lights/appliances.

So it's unusual ("unique" is a high bar) in that it's one of the largest privately-owned energy-consuming devices where existing technology can result in substantial energy savings and emission reductions.

hasmanean9• 3 years ago

In theory burning high grade fuel to produce heat is stupid. CHP (combined heat and power) systems have more than 90% efficiency even with yesterday’s technology because all the inefficiency is used to heat your house.

The temperature of a natural gas flame is 2770C. Using it to heat a house to 30C is ridiculous. Instead you should run a gas turbine off of it to produce electricity. The exhaust should run a steam turbine which makes more electricity. Then a heat pump can capture more energy from the exhaust (and from your bath water etc) to pump more heat into your house. The electricity can be used to charge an electric car or run a gpu inside your house (and produce even more heat).

Heat pumps should be utilitarian and 10x cheaper, and used in multiple places. They should not be something you “invest” in with a 10 year payback time.

Angostura• 3 years ago

The temperature of a natural gas flame is 2770C. Using it to heat a house to 30C is ridiculous.

Why?

cjfd• 3 years ago

Entropy. Delta S = Delta Q / T. An efficient use of energy produces as little entropy as possible. Here the loss is Delta Q / 303 - Delta Q / 3043. T in Kelvin.

kragen5• 3 years ago

the carnot limit for 2770°/0° is 1 - 273/3043 = 91%

the carnot limit for 30°/0° is 1 - 273/303 = 9.9%

so if your gas flame is really 2770° (which i doubt, the adiabatic flame temperature for methane in air is only 1963° and actual flames are even colder than that) you're wasting 90% of your exergy by diluting it down to 30°

also tho i do not want to go to your house if you heat it to 30°

hasmanean9• 3 years ago

Because if you have a natural gas flame in air (lets say 2000C, my previous number was wrong as someone pointed out), then you can do useful work with it.

A carnot heat engine with a hot side of 2000C(Th=2273K) and a cold side of 200C(Tc=473K), has an efficiency of 1-Tc/Th or 79%.

So you can do useful work (hopefully inside the house, where it too will eventually end up as waste heat) AND recover energy from the exhaust gas of the carnot engine--which is 200C!

Imagine burning natural gas in your furnace, vs using your natural gas to run a electricity generator and mining bitcoin with it inside your bedroom. A Bitcoin rig makes a great space heater.

chongli• 3 years ago

A modern natural gas furnace is upwards of 90% efficient. So you’re talking about building all this infrastructure (turbine generator, heat pump, etc) to capture the remaining 10% for electricity? How does that make any economic sense?

Additionally, heat pumps can already be purchased cheaply from the hardware store. These are closed systems with the refrigerant already inside. However, if you want a larger central air system then that costs a lot more because you need to hire licensed HVAC professionals to handle the construction and charging of the refrigerant loop.

bradfa2• 3 years ago

90% efficient furnaces are kind of the low end of the spectrum of product on the market now, at least in my area of the USA. My 20 year old furnace is rated 94% efficient. Pretty much every condensing gas furnace now is going to be well over 90% efficient. Even modulating furnaces with 2:1 or better turn-down ratios can maintain over 90% efficiency when running below rated output.

Locally it's not worth DIYing a heat pump install. The tax incentives and rebates easily cover the cost to hire a licensed and insured HVAC company to do the entire install for you, plus then you get to choose from a much wider selection of heat pump models which likely enable buying something better sized for your need and more efficient.

joking2• 3 years ago

gas furnace can be over 100% now, using the condensation of the fumes to provide more heat to the water. https://www.heatgeek.com/condensing-boilers-efficiency/

Anyway, is more efficient to use gas for generating energy and using that energy to heat places with heat pumps than burning gas on furnaces. If you can use the residual heat of the energy generation is even better.

switch0072• 3 years ago

Fun fact: when a £X subsidy is made available, the cost goes up by exactly £X, which is a total coincidence. ;)

JoeAltmaier2• 3 years ago

Maybe temporarily. Competition exists, the free market is real.

throw0101d4• 3 years ago

Also note that one doesn't have to go 'all-in' on heat pumps, and there are dual fuel / hybrid systems available:

A dual-fuel heat pump works in conjunction with a furnace. During the summer months, the heat pump works like a high-efficiency central air conditioner. In mild spring and fall weather, it provides cost- effective and efficient heat. As the temperatures drop in the winter months, the pump shuts off and lets your furnace take over.

* https://www.lennox.com/buyers-guide/guide-to-hvac/glossary/d...

* https://www.trane.com/residential/en/resources/glossary/dual...

More of a thing when heat pumps were more expensive and/or not as capable as they are now: going down to only 5C or -10C, whereas now units can go down to -25C.

They could also still be useful in places with less reliable power (rural? coasts?), as a heat pump need more electricity, whereas a furnace just needs to power a fan and an ignition system, so a small portable generator can handle the load (or it won't tax your battery system as much).

bradfa2• 3 years ago

Dual fuel is also useful if electricity is expensive but gas is cheap and if you know what the efficiency curves look like for your appliances. I recently did this calculation and effectively when ever a heat pump would be less than a COP of 4, my gas furnace would likely cost me less money for the same amount of heat output. Our electric rates have effectively doubled in the past 5 years while gas has dropped in price. Obviously this situation is going to be region-specific and gets even more complicated with time-of-use billing. Ideally a smart thermostat would be able to consider all these variables and pick the most cost effective heat source for a dual-fuel setup but I don't think any of them are quite that useful yet.

Only a handful of centrally ducted heat pumps on the NEEP list (https://ashp.neep.org/#!/product_list/) have COP >4 at 5F outdoor temperatures.

dave3332• 3 years ago

I have a gas furnace and a separate AC unit - I wonder can I replace the AC unit with a heat pump and keep the gas furnace? I could keep the existing thermostat and have the heat pump work with a new second thermostat so I can set the heat pump to kick in the heat at a lower temperature than the gas furnace. Maybe turn the gas furnace thermostat down once a month to operate it to prevent problems.

mschuster91• 3 years ago

Yes, of course, that's the "dual fuel" setup mentioned in the article. In Europe, it's very common as we mostly use water to distribute heat. Either connect the heat pump and the gas furnace in parallel and run whatever you want depending on circumstances (i.e. normal operation is handled by heat pump, but the heat pump kicks in at low temperatures or high load), or run them in series with an optional bypass (i.e. the heat pump heats the water prior to entering the gas furnace).

throw0101d4• 3 years ago

Note that your furnace needs to be designed to support this.

Generally it is extra logic so that you have a "Heat_1" source (HP) and a "Heat_2" source (switch to burning).

refurb• 3 years ago

I've never tried one, but they seem uniquely suited to clothes dryers.

Use the cold side to dehumidify the air, then pass it over the warm side to heat it up.

Net-net, no extra heat in the room it's operating in (beyond the motor and such), and a nice self-contained unit that doesn't need external venting.

shellfishgene2• 3 years ago

Most modern clothes dryers work exactly like that.

frankus4• 3 years ago

A number of newer ones are ventless (although still very much the minority in North America), but only some use an actual heat pump to recycle the heat. IME most of the cheaper ventless dryers just reject the heat (but not the moisture) into the room they're operating in.

This is still a win because it doesn't depressurize the house (any air you vent out of the house is eventually replaced by outside air, sometimes via dirty areas like crawlspaces and attics). But the heat pump ones can run off of a low-power (~1500W) circuit whereas the condensing ones typically need a higher power (~5kW) circuit.

timbit42• 3 years ago

You can also get heat pump water heaters, although they take heat from the room.

foobiekr• 3 years ago

I've wondered about these - why don't they do the same split that HVAC pumps use? It seems really bizarre as a design. Components would also mean replacing the tank would be more cost effective and circuit routing would be easier.

losvedir• 3 years ago

Hey, that's fun. That's the first "(2023)" I've seen on HN.

This is a pretty useful guide for me since I've wanted to look into getting a heat pump for my home. But it doesn't get into the first stumbling block that much: _finding_ a contractor! It mentions contractors some, but doesn't talk about those that do heat pumps vs those that don't. Around where I live in Northern Indiana, I haven't really found anyone that's got a ton of experience installing, working with, and (importantly!) repairing, heat pumps.

JCM9• 3 years ago

Generally a fan of heat pumps but the big issue remains where does the electricity come from to power them. Burning coal or gas to make electricity to power a heat pump isn’t great. Cost wise too I know a bunch of folks that switched from gas to electric heat pumps only to be shocked by their electric bills.

Highly efficient natural gas setups remain much better for many settings.

mechagodzilla• 3 years ago

Given the lifetime of the equipment and the relatively rapid transformation our power grid is undergoing, there are probably few places in the US where a heat pump doesn’t come out significantly on top emissions-wise. With an entirely natural gas grid, you only need a COP of 2 or so to beat the most efficient direct natural gas setups. Ten or fifteen years from now coal generation will probably barely exist in the US and we will have another few hundred GW of wind and solar.

Lutger2• 3 years ago

It isn't great, but perhaps surprisingly so using gas to create electricity and the electricity for a heat pump, is still a lot better than using a regular gas boiler. In other words, you'll get more heat out of a m3 of gas when you use it to create electricity and power a heat pump with the generated electricity, generally speaking.

So it is an improvement even if the net is 100% dirty. But it isn't, even in winter we can get a lot of electricity from renewable sources.

I think there are two big issues with heat pumps: they are expensive and require well insulated homes. Both problems can be solved.

bluGill2• 3 years ago

My local utility generated more wind electric than all customers used last year. The rest of the US needs to catch up.

ThatPlayer• 3 years ago

Having multiple possible sources for electricity is an advantage for price stability. For example California's gas prices tripled this time last year.

In general I think natural gas prices will continue to go up as people switch to electricity or more efficient gas setups. Less gas usage means additional fees for infrastructure. As prices go up, more people will switch. It's a feedback loop. At some point it won't be worth it to run the infrastructure for natural gas anymore.

prepend• 3 years ago

I had a furnace die and had to replace it last year. The hvac company was really down on heatpumps and said that due to the climate (doesn’t get too cold in the winters gets really hot and muggy in the summers) the heat pump would be less efficient than a traditional furnace and AC.

I like my hvac company so didn’t push too hard but wondered if this was true or just their inexperience.

Lendal• 3 years ago

Not inexperience. Motivated reasoning.

projektfu2• 3 years ago

They don't like heat pumps mainly because their customers "don't feel the heat" from them. The heat comes out at lower than body temperature (85F/30C) so the customers don't feel like they're really working, whereas a gas furnace or electric heater usually heats to 120F/50C. So, customer satisfaction is often lower even though they are saving money and polluting less. But, you know, that 85F is plenty to heat a room to 72F and keep you warm.

avidphantasm• 3 years ago

Our Mitsubishi Hyper Heat heat pumps put out noticeably warm air, definitely warmer than 30C.

caleb-allen• 3 years ago

I can't imagine that a traditional furnace and AC could be less efficient than a heat pump, unless you almost never turn your heat on—a heat pump is many times more efficient, in terms of energy consumption, than a traditional furnace.

That said, if it's rare to run your heating then a standard AC unit is probably marginally more efficient than a heat pump for just the cooling operation

infecto2• 3 years ago

Taking it a step further it makes sense.

So far most heat pumps are a step up in price in the US compared to the traditional furnance/Ac setup. If you only needed the furnace replaced it might make sense to only replace that and not spending the extra multiple to replace the entire system.

jogjayr• 3 years ago

Lies like that make my blood boil. Not-too-cold winters are perfect for heat pumps.

pjc507• 3 years ago

If you already have AC ducting/plumbing, you're an ideal candidate for "reversible AC" heatpumps.

bluGill2• 3 years ago

If it doesn't get very cold in winter that is ideal for a heat pump. Heat pumps lose efficiency as it gets cold, and even the best stop working completely at somewhere around -20. If it might get that cold you need a backup source of heat.

HVAC companies don't like heat pumps because they cost more (mostly for no good reason - but you may need a larger heat pump and air conditioner), don't put out as warm of air as a gas furnace, and are slow to change temperatures (don't not get a setback thermostat with a heat pump!). Customers do not understand them and end up unhappy and complain about them. However if you get one anyway understanding the limits you will save a lot of money.

stevekrouse• 3 years ago

From the author of that article: https://heatpumpshooray.com/

DanielHB• 3 years ago

I am always amazed at how many people know this stuff deeply, I feel most people actually live in apartments with either central building heating or district heating and never ever need to think about this stuff.

Especially considering buildings have less wall/roof area to lose heat from on a dwelling by dwelling basis, even a small-ish building with gas heating with average insulation would still be much cheaper to heat than a house by square meter.

Tagbert• 3 years ago

In the US, housing is heavily biased to single-family houses.

About 81 million detached single-family vs about 30 million multi-unit housing. https://www.statista.com/statistics/1042111/single-family-vs...

bob1029• 3 years ago

In the US, you have to be fairly diligent as a homeowner to not get taken for a ride by the various HVAC technicians.

The more you know about your own system, the more you can save. Even if you don't intend to do any work yourself.

2-718-281-8284• 3 years ago

are heat pumps interesting to you folks because you have one or think about getting one or because the technology is in some aspect particularly impressing/counterintuitive/ingenuous? i ask because this topic is popping up regularly and so far i fail to see why.

pjc507• 3 years ago

Rather like electric cars, they're a technology lots of people are thinking about getting for environmental reasons, but also a big fixed investment so people are keen to understand.

stinos4• 3 years ago

the technology is in some aspect particularly impressing

Yes, because for every unit of energy you directly put into it (in the form of electricity) it outputs more energy (in the form of heat). Which is unlike any other typical heating system, which usually puts out less or at max the same amount.

2-718-281-8284• 3 years ago

like a perpetuum mobile?

JoeAltmaier2• 3 years ago

The labor issue might be due to the seasonality of the business.

(The labor issue: 300,000 HVAC professionals in the USA but just 145,000 companies).

In fact, the business is initiated just two days of the year! The first hot day of summer and the first cold day of winter. When somebody's old system breaks and they find out exactly when they need it most!

So it's always an emergency, and always when it's very unpleasant to work outdoor.

Seems clear why nobody is going into the business. One of those 'dirty jobs'.

Maybe a business model that spread things out? Like, a contract to support heating and cooling year-round, schedules upgrades, does periodic testing to anticipate breakdown.

I imagine now it's more like folks that have snow-plow trucks, promise to plow out your parking lot after each big snow. They work just a couple days a year in Iowa, and have regular jobs the rest of the year. The companies are less than half a dozen trucks typically, with a huge demographic spike at 'one guy, one truck'

ortusdux• 3 years ago

I replaced my electric water heater with a heat pump unit, and it paid for itself in 2 years.

ppsreejith3• 3 years ago

This doesn't explain how they work though? I've found the following simplified model of how heat pumps work useful, and why they have > 100% efficiencies (Typically 300% - 400% or more compared to burning/ resistance heating which can only reach 100% efficiency).

Heat always flows from a high temperature to a low temperature. However, we want heat to go the opposite way (i.e. from the cold outside to our warm houses). There's a technique to do this. We use a gas (the refrigerant) to transfer heat.

We first expand the gas (which cools it) until it cools below the cold outside. We then bring it near the cold outside where it now starts absorbing heat until it matches the cold outside temperature. We then move the gas and compress it until it's temperature matches/exceeds our desired warm inside temperature. Then, we bring it to the warm indoors where heat will now flow out of it.

During the entire cycle, the gas is inside a closed loop. It exchanges heat through radiators. The compression & expansion cycles uses energy (technically they can be offset against each other a bit) which is added to the gas (conservation of energy) raising its temperature.

Thus by supplying a little electricity, we're able to move heat from the cold outdoors to the warm indoors. The high efficiencies are because for using X units of energy, we're able to heat the house by X+Y units where Y is the heat transferred from the outside. Typically Y >> X.

cubefox2• 3 years ago

By that measure of energy, burning oil or gas also has >>100% efficiency, as you only need energy to get it out of the ground, transport, and to light it. The energy stored in the oil is analogous to the "outside heat" for heat pumps.

duckmysick• 3 years ago

That's the thing though: the energy is stored in natural gas or oil but I still need to extract it. I can't heat my room by pumping it full of natural gas or filling it with oil.

To raise the temperature of my 300 square feet room by one degree I need the same amount of energy, no matter the source. But the ways of delivering that energy aren't the same.

If I have a simple gas burner, I need to know how much gas do I have to burn to heat my room. It will keep me warm, but it's not a good idea. Burning gas with a flame makes other gases that I don't want inside. I need to vent them, but I will lose some heat through that.

I can also get a gas furnace that condenses those byproduct gasses in a second heat exchanger for extra efficiency. Maybe seal it up better too. It needs a little electric power for ignition, so I need to take that into account. But overall, it would be more efficient. I would need less gas to heat my room.

Even though I'm using gas in both examples, the efficiency is different. It depends on how I convert that gas into heat.

I can also burn that gas in a generator to produce electric power. Then I can use that electric power for a resistive heater. Not a great idea, but it's an option.

I don't have to burn the gas myself. I can delegate generating power to a gas-fired power plant and buy power from them. And I can use a heat pump instead of a resistive heater. My heat pump will use less power than a resistive heater, so that's good, I suppose.

The question remains: how much gas do I (or a power plant) have to burn to heat my room. The answer depends on what do I use the gas for and how. That's the efficiency.

stubish• 3 years ago

The measure really is how many joules of energy is required to heat something a certain amount of joules.

By burning oil or converting electricity to heat, 1 joule of stored chemical or electrical energy converted to heat energy will raise the heat of that something by a maximum of 1 joule. A maximum of 100% efficiency.

By using 1 joule of energy to compress cold gas into warm gas, we can raise the heat of that something by 3-4 joules. Moving heat energy around is more efficient that generating heat energy. Commercially available technology 300%-400% efficient.

ppsreejith3• 3 years ago

The energy stored in the oil is analogous to the "outside heat" for heat pumps.

This isn't correct. Here's a thought experiment to clarify:

If we burn X MJ of oil, we transfer X MJ of energy as heat to our house.

Otoh, if we set up a generator (say 40% efficient) which produces electricity from oil and dumps waste heat into our house, and use that to power a 300% efficient heat pump, we get 0.6X (generator waste heat) + 1.2X (300% * 0.4X) = 1.8X MJ of heat using the same X MJ of oil.

Thus,we get an additional 0.8X MJ of heat (80% extra heating) from the same X MJ of oil just by using a heat pump (& generator) compared to burning it. I.e we're using the energy stored inside the oil more efficiently.

Projectiboga3• 3 years ago

It's able to do this via a temp change as part of the compression cycle. When gas expands it's container gets cold. These systems can move heat from outdoors to inside in cooler weather. Your Air Conditioner doesn't make cold, it moves your heat outside. So being able to move or collect heat is how efficiencies over '100%' can happen, it isn't free just more efficient than space heaters.

peter_l_downs• 3 years ago

I had heat pumps added to my home this past summer, primarily to provide air conditioning. This article is a good overview of what I learned in the process. I'll add a few lessons:

- Get a few quotes and iterate on the plan. Save the contractor you'd most prefer to work with for last, because you'll have a much better idea of what you want by then, and your knowledge will save you money.

- There's a fun puzzle to retrofitting older homes (no existing ducts): where you place the lines, where you place the units, and where you place the heads are all variables to play around with. This is part of the reason for getting different quotes. Only the last two contractors I spoke with were able to come up with ways to keep all the external lines on the side of my house and away from the street. Only the very last contractor offered a ducted system for bedrooms, so I have head units downstairs but the upstairs is vented.

- No one will run a real Man J calculation, they all use proxy calculations. This should be fine but you almost certainly want to slightly undersize your system. If your system is always turning on and then turning off (because it is oversized and heating / cooling the room very quickly) you'll end up with humidity and mildew problems, you want it to be running "low and slow" while it's on.

- They work amazing for air conditioning. For heat, your existing boiler + radiators is often nicer and more cozy. It's also often cheaper — heat pumps are electrically efficient, but natural gas costs vary significantly by location and for me (~Philadelphia) heating with my boiler is a lot cheaper than doing it with the heat pumps.

- I live in an older home, so before I installed heat pumps I had to replace my ancient windows for modern ones that didn't constantly leak energy. I'm happy with the results but it adds a lot to the startup cost.

amluto• 3 years ago

Even Manual J (in my quite limited experience) can give wildly inflated results. For example, if a big window has a tree in front of it or a reasonably reflective or insulating window treatment (and you close it on a hot day!), then your Manual J software may estimate the heat load as if the sun were shining full blast through the glass all the time and give a huge number.

I intentionally had a contractor install a unit that was undersized per Manual J in a room, and, as tested during a nearly-record-breaking heat wave, it kept up without coming close to its limits.

Fortunately, a lot of modern systems have respectable turndown ratios (better than 5:1 is not that hard to find), so as long as you use controls that can operate the system all the way down to minimum power, oversizing is not that bad.

Kirby64• 3 years ago

Modern inverter based heat pumps are perfectly fine to oversize. Since you can adjust the speed of the compressor, you just run the compressor slower if you want to 'undersize' it. There's little downside aside from cost to oversizing these days, and in many cases it may be necessary to oversize the cooling side to provide enough heating in the winter.

christkv2• 3 years ago

We are building a new house now and the heat pump will actually provide heating a cooling through panels installed in the ceiling and walls.

sokoloff10• 3 years ago

Presumably not in a highly humid summer environment? Radiant cooling is limited to dew point, so works poorly in humid environments (or requires whole-house dehumidification to lower the dew point).

vhodges2• 3 years ago

Sigh, I need this a few week ago ;)...I just replaced my failed gas fired furnace with a Fujitsu XLTH 3 ton ducted mini split in the Fraser Valley (Mission BC).

I only got 2 quotes (and spoke with a third, but not quoted beyond ballpark). I ended up going with the local installer (which was the lowest, but I also worked with them on the furnace and liked them anyways).

It ended up being 20k CAD installed. If we're approved for all of our rebates (likely) we'll get 11k CAD back for a net of 9k which isn't too bad.

Our unit is supposed to be rated for 110% of heating capacity at -15c. We'll see , it's supposed to drop to -8c or so later this week :) We're looking forward to having cooling this summer (which we've never had)

barbazoo5• 3 years ago

As a valley neighbour I'd be interested in an update when the time comes.

vhodges2• 3 years ago

Now that it's warming back up a bit, here's that update:

It was mostly okay. It kept working even with the -20c windchill and was always putting out heat.

It's kind of subjective but I feel it struggled a bit eg the 'room' temperature shows a degree or two below the set temp. It never felt cold in the house (but a bit cooler?)

The sensor is probably in the control unit which IS in the hallway over the garage (and that side of the house always seems a bit cooler) so take that info with a grain of salt.

1970-01-013• 3 years ago

The more you think about it, the more it makes sense to harness geothermal. A big breakthrough there could benefit our environment more than any other tech, except fusion.

simonebrunozzi• 3 years ago

Cheaper digging would be the breakthrough.

1970-01-013• 3 years ago

Or vaporization of bedrock with a super laser

barbazoo5• 3 years ago

For residential purposes it seems to only require a depth of <2m [1]. Is moving dirt here a main cost?

[1] https://www.energy.gov/energysaver/geothermal-heat-pumps

barbazoo5• 3 years ago

Do you know what current limitations of residential geothermal are? From looking at https://www.energy.gov/energysaver/geothermal-heat-pumps it looks like you'd need quite a bit of space, so basically single family homes with somewhat of a yard.

For bigger setups it would make more sense to capture the heat locally and distribute them to a whole neighborhood given how much deeper it would need to go.

1970-01-013• 3 years ago

The vertical system looks to be about the size of an average driveway or garage. Done at scale, mainly for new construction, system sizing isn't a problem.

m3kw9• 3 years ago

From the comments and article, heat pumps are not ready for prime time and also still version 1.0. And you know what first time adopters have to go through

turtledragonfly• 3 years ago

Apropos of nothing, I had a not-great experience switching from an oil furnace to heat pump. Maybe somebody else going through research will benefit from my woes. Some day I'll make a blog post for it:

1. Noise levels (inside)

* Fundamentally, a heat pump runs more often than a furnace. So, air is semi-constantly blowing out of your vents, rather than a few bursts throughout the day. Also, the air is tepid, rather than warm. Previously, there was a "yay, the furnace is on" moment of enjoying the warm air. Now, it's more of a "jeez when will this thing shut up again?" throughout the day. It reduces my quality of life.

* One of our vents points at my back where I sit to work. With the furnace, that was enjoyable. With the heat pump, it's a nuisance. I taped over the part that blows on me. Similarly, we have a vent in the bedroom that we mostly keep covered with a pillow these days, due to the noise.

* In documentation, noise is often measured in decibels — indicating max loudness. And by that measurement, the heat pump is no worse than the furnace (maybe even a bit quieter). But the fact that it's on near-continuously at that noise level is what causes my annoyance. So, it's not just loudness, but also how continuous it is.

* We had existing ductwork, so the heat pump's air handler uses that (just like the old furnace). This is a common situation, but what nobody mentioned, across multiple estimators, is that it's likely the old ductwork will be "under-sized" relative to the new system. This means higher static pressure, and importantly, more noise at the output vents. Talking to the technicians, this is a bit of a crapshoot — you might get lucky with noise levels, or might not (like me).

* Loudness will also vary depending on how far from the central unit you are (my house is fairly small), how many vents there are, and various other factors.

* In theory, you can determine if the above will be a problem by doing measurements beforehand. None of the estimators mentioned this; they just want to sell you the system, of course. I didn't realize until too late that you can probably find someone, pay them a few hundred dollars, and get this information upfront. There's a whole science to it, with specialized tools. Look up "Manual J, S, D, T measurements," for a starter.

* However, even if you get that info, it still depends on your sensitivity to these things. For instance, my wife is much less bothered by the noise than I am.

2. Thermostats

We got a fairly modern "communicating" system. This means the outdoor and indoor units talk to each other, allowing better efficiency.

This sounds nice, but what it means is that you will be locked in to your vendor's choice of thermostats, since the communication protocol is proprietary. These are generally more expensive than the alternatives, and you won't have many options — perhaps only one.

If you get a "non-communicating" system, you will be able to try various different thermostats — eg: a simple one from your hardware store, or a Nest one, etc.

3. Other

* The old oil furnace was a simple machine, with a lifetime warranty on the heat exchanger (basically a hunk of cast iron) and can basically last forever with decent maintenance. The new heat pump has a 12 year warranty, and the system might last 25 years with good maintenance. The HVAC estimator seemed proud of this, but to me it doesn't seem like an especially long time.

* If you use old ductwork like mine, it may not be insulated to modern standards. This is both a noise issue and potentially a condensation issue when the AC mode is running.

* It's very difficult to know when the "emergency heat" mode is being used — where resistive electrical strips are used to generate extra heat, if the heat pump isn't producing enough. This mode is much more expensive than the heat pump alone. It boggles my mind that such simple (and useful) information is so hard to obtain.

* If you want to get government subsidies, do your research about what exact make/model is covered by it. Ironically, sometimes the more modern and efficient systems are not subsidized, presumably because there is some lag to update policies.

* Generally, remember that the estimator who might come to your house is a salesman, first and foremost (:

4. Pros

Okay it's not all bad; some positives include:

* AC in the summer. Probably the biggest positive.

* No dependence on oil — both for cost and environmental concerns and risk of tank leakage (ours was aboveground, so less of a worry)

* No carbon monoxide worry, since there's no combustion going on.

But overall, I'm not sure it was worth it for my case.

briHass• 3 years ago

The case of duct work not being sufficient for a oil/gas -> heat pump conversion is pretty common. A heat pump, especially one of the conventional split types (non-minisplit) generally wants 300-400 CFM of airflow per ton. So, a 3 ton unit is happiest moving around 1200 CFM of air. Lower can cause issues with ice-up in AC mode or high pressure shutdown in heat mode.

There are rules of thumb for duct work that are pretty easy to use to estimate. A 6" round duct, for example, is designed for about 80 CFM (not counting any restrictions on the register/grille.) That 3 ton system is going to need 15 'takeoffs' of 6" duct to handle that air. Adding more duct work can be expensive if the majority of it isn't in unfinished locations like a basement or attic.

vizzah2• 3 years ago

Is there a conspiracy? Why everyone is talking about heatpumps these days? Including in the UK.

In Europe air conditioners come with heat-pumping functions since ages ago.. all installed aircons can heat or cool. But I personally found such heating ineffective and lame.

What's going on?

barbazoo5• 3 years ago

I think it gets clicks. Lots of people are passionately for/against them for ideological reasons.

cpncrunch• 3 years ago

Why everyone is talking about heatpumps these days?

Because of their efficiency. They are typically 200-400% as efficient as electric resistance heaters, because the energy is used to move the heat from outside.

I personally found such heating ineffective and lame.

If it's a proper heat pump, the heating won't be ineffective or lame. It should pump out air > 30C, and is sufficient to keep your house at 21C even when outdoor temp is 0C.

vizzah2• 3 years ago

but it should be on most of the day, for the air indoors to remain at 21C. Once stopped, the air cools off very quickly, compared to other heating methods. Underfloor heating is a best heating option in my opinion, perhaps mixed with a couple IR panels on the walls. With heatpumps it takes too long for the the warm air to descent and make legs/feet feel comfortable :(

kyleblarson• 3 years ago

I don't have an idealogical horse in this race, but I bought a ~2500sqft home a few years back in an area where summer highs can get to 100f and winter lows can reach -25f. The house only had a 20 year old electric furnace and no AC. Replaced it with a large heat pump system with a new electric furnace for backup heat when it gets super cold. Also included an air filtration system. It was a big cash outlay, but totally worth it as we now have AC in the summer so we can keep windows closed when the smoke is bad, the filtration system works really well for the smoke, and the system almost never needs to use the furnace backup. Speaking with the previous owner, the winter electric bill savings have been around 30%.

pkulak• 3 years ago

I'm surprised it's only 30%. Even a COP of 3, which is pretty modest for a modern heat pump, would be 60% savings (abouts, not sure if my math is right).

pandaman• 3 years ago

Most houses consume electricity for the purposes other than heating too.

sokoloff10• 3 years ago

People commonly (by default) compare electric bills on $$ rather than on kW*hr, so an increase in rate would reduce the savings-as-compared.

Different baseline electricity use and thermostat preferences could play a significant role as well. (Previous owners may have gone for a lower daytime setting and a deeper setback because of the inefficiency. A new owner with a more efficient system may quite reasonably choose to bias towards greater comfort than the prior owner did.)

Projectiboga3• 3 years ago

New guy might be getting more comfort by heating more while still using less total electricity.

gavin_gee2• 3 years ago

pretty good post. The big gap is a section on noise. Citys like seattle have incredibly tough noise limits at property boundaries for heatpumps. with many high density single family houses close to the property line. it makes it difficult to find a quiet heatpump. (stupidly there are noise limit differences for a heat pump vs an AC unit)

As far as I can tell there are no efficient heatpumps available on the market that can sit legally less than 6 feet from the property line in Seattle and supply a 5 ton system

r0m4n0• 3 years ago

Converted my house to heat pump last year and seen a full year of what the cost savings look like. Saving 50% over gas in the winter, saving 30% in the summer over my old AC. I don’t miss the furnace firing up and the noises it would make when it pushed tons of hot air. Getting much more constant temperature instead of being hot sometimes and cold the next.

Negative: Not a fan of the weird noise the unit outside my bedroom window makes at a more consistent rate through the winter and it annoys my neighbor too.

Overall got the home warranty to cover about 10k of the 16k replacement, after learning about going to arbitration here on HN!

Definitely happy with the conversion overall thus far. Jury is still out on long term reliability

c_o_n_v_e_x• 3 years ago

For someone who's not in the industry, the Author has done a reasonable job.

I'd add a few things:

- Heat pumps have been around a while. In the southern US, there are lot of older HVAC techs with a negative perception of HPs based on problems with older technology. Older HPs had less of an ambient operating temperature range, in which case the emergency heat would activate, reducing savings.

- Re: fragmented markets, different states/cities/towns/municipalities have different rules, processes, procedures, etc.

- Re: the desire for drop-in installations, the construction permitting and inspection process is a big fat roadblock which is linked to the problem above.

theogravity• 3 years ago

Bay area resident here that had a heat pump installed last month. The heat pump, air pusher, comm units + labor came out to $23k for the highest 4 ton Trane efficiency unit (no heat strips either). The labor cost probably was 100%+ of the system itself, so I feel the article has a degree of accuracy to it.

rdsubhas• 3 years ago

Heat pumps are simple, easy to understand, efficient (uses very little energy) devices.

But it still blows my mind every time — that we can use the heat of the sun to cool our homes. What a wonderful time to live in!

Heat pumps, more than you wanted to know (2023)

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