alt.hn

2/1/2026 at 6:15:40 PM

Pretty soon, heat pumps will be able to store and distribute heat as needed

 https://www.sintef.no/en/latest-news/2026/pretty-soon-heat-pumps-will-be-able-to-store-and-distribute-heat-as-needed/

by PaulHoule

2/2/2026 at 8:24:41 PM

They should've used lasagna. You could be in a tundra heating it over a fire and, as long as you get it sufficiently and consistently hot, it'll still burn your mouth 20minutes later.

by chankstein38

2/2/2026 at 9:11:20 PM

I was recently wondering if any particular type of food contributes to mouth cancer prevalence and I concluded that at the top of that list would be be lasagna and cherry tomato on a pizza/in a soup.

by cromka

2/3/2026 at 8:43:02 PM

Why?

by sandinmyjoints

2/4/2026 at 12:33:42 AM

Mouth burns or bites can lead to cancer

by cromka

2/3/2026 at 4:57:25 PM

It's actually the same physics: layers, trapped moisture, and phase changes holding onto heat way longer than you expect

by BrtByte

2/3/2026 at 1:30:51 PM

Try Toast Hawaii. The weird mix of ham, pineapple and cheese the Germans make.

I am still convinced the lava cheese insulator is there only to burn people's insides with boiling pineapple.

by Joe_Cool

2/3/2026 at 1:58:10 PM

But that’s because of the water content of pineapple, so now we’re back at water..

Although pineapple flavoured floor heating does sound delicious.

by moi2388

2/2/2026 at 10:34:23 PM

And yet, if you make it like I do, there always manages to be one piece that is ice cold while the rest is shockingly hot. Even if you're start with warm ingredients.

Physics does not apply to lasagna.

Also I suck at making lasagna.

by Loughla

2/3/2026 at 12:45:30 AM

I don't know how you cook your lasagna, but cooking for longer at a lower temperature usually results in more even heating than cooking for less long at a higher temperature. (This is one of the reasons microwaves are so terrible at heating evenly.) If you're not already, that may help.

(I also imagine using the circulation in a convection oven might help as well. Also, preheating your oven! Even if it's a toaster oven.)

by LoganDark

2/3/2026 at 2:48:41 PM

Preheating isn't really important for most things, essentially anything that doesn't specifically call for very high temperatures. The main thing it gets you is more predictable baking times which is important if you need a number to print on a box that will work in most ovens but less so when you just leave something in the oven until it is done.

by account42

2/3/2026 at 1:01:09 AM

Microwave tip:

Use the power button to select a lower power level, and cook the food for longer.

by esseph

2/3/2026 at 2:17:49 AM

Only works adequately if your microwave is the rarer kind that actually lowers the power (inverter), instead of just switching between 100% and 0% repeatedly.

by dataflow

2/3/2026 at 4:49:30 AM

This should depend on the frequency of the switching, if it is every few seconds it should behave sorta the same

by afiori

2/4/2026 at 4:11:03 AM

Yes but I've never seen it be every few seconds. Every time I've seen, it's quite prolonged.

by dataflow

2/4/2026 at 1:06:12 AM

Another important part is that a lot of microwave recipes specifically state to leave the food in the microwave for a period of time after it's done cooking, and often stir it after that. Almost no one actually does that.

Most people think they should be able to put food in, nuke it at full power for as short of a time as possible, and then immediately shove it in their face with no consequence and we all know that doesn't work yet most of us will keep doing it anyways.

by wolrah

2/3/2026 at 3:07:15 AM

I don't have the fancier inverter style. Setting a power level still works pretty well even though flawed. Drawing out the overall cooking time still manages to get things more evenly heated in the end when you give the food time to distribute the heat throughout the food.

Cooking food for 2 minutes at 50% power gives a noticeable difference in average temperature compared to cooking food for 1 minute at 100% power and waiting a minute.

And I don't always know what it decides to do as far as turning the magnetron on and off on its sensor modes, but it'll spend a while doing automated reheat and potatoes and what not and it'll be dang near perfect every time.

Don't get me wrong I'd love an inverter microwave, truly a better option. But its not like the duty cycle process has no impact.

by vel0city

2/3/2026 at 3:34:38 AM

It's funny, because the inverter microwave is actually cheaper to build nowadays. It uses a small switching power supply to generate the needed voltage to run the magnetron at different power levels. The older style duty cycle microwaves use a huge transformer to generate the high voltage, which makes them way heavier and more expensive due to all that copper.

by chongli

2/3/2026 at 5:01:59 AM

My microwave is over 20 years old and still working fine even with its computerized automatic modes. Modern versions of the product line are inverter based. Whenever this unit fails I'll probably replace it with the modern inverter version. I've used it at friends places, it's quite nice.

It's a GE Profile model FWIW. It seems like a good product line from my experiences. The matching oven has also been a good performer overall.

by vel0city

2/3/2026 at 1:47:42 AM

toroidal lasagne microwaves better

by goopypoop

2/3/2026 at 2:12:01 AM

Spotted the Brit.

by stavros

2/3/2026 at 4:30:44 AM

u wot m8

by goopypoop

2/3/2026 at 3:26:13 PM

To whatever degree you are serious, this can be a phase change thing.

Cheese melting takes energy Cheese freezing, releases energy.

So you do actually get the temperature to remain at the melting point of the cheese for a longer period of time if you have enough % cheese to be significant.

by sokka_h2otribe

2/3/2026 at 2:03:35 PM

Sometimes I wonder if the people trying to create a fusion reactor have ever made a baked potato, because I swear it's halfway there.

by mekdoonggi

2/2/2026 at 11:23:38 PM

It uses phase change (solid to liquid) to store heat at about 200 kJ/kg. Compare this to heating water in a boiler from 10c to 60c - stores 209 kJ/kg.

So we already have an effective way to store heat which can work for decades without servicing and is also cheap to produce (in terms of money and energy consumption).

by 5ersi

2/3/2026 at 9:26:04 AM

What about heat per unit of volume? Seems like the selling point is that a pretty small box can service a whole bathroom. Presumably it has a higher density than water and requires less insulation?

by elric

2/3/2026 at 11:31:23 AM

I think this is the most crucial part. External heat pumps are OK - people install air conditioners everywhere already - but most houses/apartments aren't set up for large water tanks. The interior heat storage needs to be comparable in size to the existing gas boiler.

by leoedin

2/3/2026 at 7:59:23 AM

I don't know why these aren't used more in building fabric. There's a youtuber who makes these phase change solutions out of various salt mixes aiming for the correct change temperature for a specific application. Eg he made panels for his shed roof (keeps it cooler in sun, warmer at night). Obviously this works better to smooth out large, reliable daily temperature swings, and offers little to someone in a constantly hot or constantly cold place.

I live in Ireland where night/day temperature swings are small. To cool my attic on a hot summer day I'd need to move that heat into a large water tank that gets used for laundry, cleaning, showers etc and is refilled from cold mains water. But fitting an air to water heat exchanger inside my attic would be a big expense and I would have to make sure I didn't freeze the attic.

Regular air to water heat pump could be hooked into my existing tank I suppose?

by raffraffraff

2/3/2026 at 10:50:17 AM

The name of the YT channel is NightHawkInLight[0] btw. Absolutely worth checking out. He creates materials with extremely useful properties from household materials (eg. PCM (high heat capacity), highly reflective paintings, Aerocrete (high insulation/fire resistance), ...)

[0]: https://youtube.com/@Nighthawkinlight

by TobTobXX

2/3/2026 at 2:20:33 AM

There are also existing commercially-available residential units (e.g. Ecombi or Steffes) using ceramic bricks that are in the ~450 kJ/kg range.

by Marsymars

2/3/2026 at 3:48:46 AM

Note for the confused: Ecombi achieves this by heating the bricks to dramatically higher temperatures using conventional resistive heating elements, thereby storing more energy, even though the specific heat capacity of any ceramic material is dramatically inferior to that of water.

But, as a result, Ecombi has a much lower system efficiency than a heat pump, since it's essentially just a space heater pointed at a rock. It only makes sense for jurisdictions with time-of-day variable pricing of electricity, and trades off simplicity and low initial purchase price for lifetime cost.

by sbierwagen

2/3/2026 at 3:58:15 AM

Thanks for the notes! I've seen them at other people's homes, but that's about the extent of my knowledge about them. (And I quickly googled a spec sheet to calculate a kJ/kg value.)

by Marsymars

2/3/2026 at 5:31:48 AM

I suppose that efficiency whammy is worth it if you can use it to smooth out the duck curve. If power rates go negative then you'd be a fool not to run a space heater pointing at a rock!

by MengerSponge

2/3/2026 at 8:37:23 AM

Does heating water in a boiler work well with a heat pump? How about a release of energy 10 hours later (peak solar at noon, to first shower the next morning)?

I actually don't know the answer. I'm just thinking that there must be more to it, if the answer was as simple as "just heat water".

by jcattle

2/3/2026 at 8:57:03 AM

It does. However, the hotter the water becomes, the less effective the heatpump becomes. With anything beyond 60C becoming very inefficient.

With hot water tanks, they are unfortunately pretty badly insulated as well, with some of them loosing heat very quickly. Depending on how you plan on using that water, you also have to make sure the temperature never dips below ~60C to avoid legionella from spreading.

I actually think that heating your home slighly higher than you‘d usually do is the simplest and most effective approach, assuming it is properly insulated. Just rise the target temp for 1-2C when the energy is cheap and reset it once it isn‘t. Probably not as efficient, but extremely simple to implement.

by moooo99

2/3/2026 at 9:08:22 AM

I have two heat pump water tanks, one Rheem and one AO Smith (our local utility heavily-subsidizes these, with a net-cost less than a standard tank water heater).

They both are rated for annual kWH usage less than the US EPA yellow label can display (for their category of tanked water heaters, i.e. competing mostly with resistive heating models).

Annually water heating is about 3% of my energy consumption.

by ProllyInfamous

2/3/2026 at 2:40:43 PM

Do you prefer one to the other? I’m in the market

by stratosmacker

2/3/2026 at 6:56:11 PM

The AO Smith (retail $1678) cost $250, after rebates (available to all SFH in any of TVA's power sellers, typically between Thanksgiving and NYE). With rebates the Rheem was $1000 (and is two years older).

Without rebates, they're similarly priced.

As far as reliability, they both have decent warranties and backup heating elements. Both heat water without internet connectivity. Similar performances (as far as heat output).

Overall, I feel the AO Smith is more customer friendly. Definitely easier to install:

1) AO has both top and side water connections; Rhm has one top and then one side connection (why?!)

2) AO's venting connections are far superior to Rheem's (which require custom/expensive adapters if installed in spaces <700sqft) — AO just has two standard 8" duct connectors on top... so much easier/cheaper to install into a closet. Rhm's top slit needs a $120 plastic adapter, and then ejects to the side (of a 24"D cylinder) [again: why?].

3) Rheem will not stay in ELECTRIC-HEAT (only) mode, for longer than two days — it automatically reverts to the prior heat pump option (which is annoying; you can use the app and set up a schedule to "force" electric mode... but then you have to use an app). AO stays in whichever mode you select.

4) AO is just nicer presentation. Despite a few obviously less-expensive components and design decisions... the AO is better thought-out. Just as an example, the Rheem has a threaded 3/4" socket for condensate, while the AO has a pre-installed (cheaper, too) drip tube.

5) The AO's electric vault is on the side (and not top) so a top leak is less likely to fill the conductors // corrosion. This is a better decision.

6) Rheem will likely last longer, despite being two years older. We'll see.

Either one will save you a lot of electricity + bonus dehumidification (while operating). I bought whichever was cheapest, the first time; now I would buy the AO even if ~$250 more expensive because the install is that much easier. This last rebate period I bought three =P

by ProllyInfamous

2/3/2026 at 3:43:51 PM

The legionella thing is a little overblown fwiw. 50 degrees is perfectly adequate, and you can go lower with very little risk if you set it to briefly bump up to 60 every week or two. Even that is not hugely necessary in a domestic setting.

https://www.heatgeek.com/articles/legionella-and-water-tempe...

by IneffablePigeon

2/3/2026 at 8:59:25 AM

> Does heating water in a boiler work well with a heat pump?

Sure, heat pump hot water tanks are a thing. Air-to-water heat pumps are less efficient than air-to-air as they need to reach higher target temperatures, but it will be more efficient that straight resistive heating by a factor of 2 at low input temperatures, and 3+-ish at high summer temps.

The primary concern would be the quality of the tank’s insulation. I would hope HPHWTs are good on that but if you’re looking into that you probably want to double check the heat loss of the tank.

by masklinn

2/2/2026 at 11:56:57 PM

one difference is that a phase change stores energy at constant temperature, which may be desirable given that heat pump efficiency is inversely proportional to temperature output temperature

by thescriptkiddie

2/3/2026 at 1:56:24 AM

I feel stagnant water would be more annoying for maintenance than something like salt hydrates.

by LoganDark

2/3/2026 at 12:46:08 PM

> But storing the heat they produce has not been possible

Many heat pumps are installed with a large insulated buffer of water (for ex. 300L), which stores heat pretty well?

And homes that use underfloor heating in concrete can store heat pretty well too. Many people use that to heat up the home when energy is cheap and disable the heat pump when it is expensive.

by jaapz

2/3/2026 at 4:55:50 PM

It's not that heat storage didn't exist, it's that this is closer to a "thermal battery" than a thermal flywheel

by BrtByte

2/2/2026 at 7:55:00 AM

Perhaps I am missing something; this product already exists as the Sunamp Thermino.

https://sunamp.com/en-gb/hot-water-solutions-thermino-range/

by chickenbig

2/2/2026 at 8:51:16 AM

It also exists, as described in the headline, as a tank of heated water.

The phase change stuff has positives like taking up less physical space but it's also a much less mature tech than storing hot water.

by ZeroGravitas

2/2/2026 at 8:35:53 PM

It's funny how useful water is for power generation.

There's heat storage as discussed here.

Or you can store cold water in a reservoir as a giant battery, pumping it up high when you've got excess power, and letting it back down to generate hydroelectricity from it later.

Or you can boil water to make steam that spins a turbine and use it to convert anything that can heat water (coal, oil, nuclear...) to electricity.

by Nition

2/2/2026 at 10:38:02 PM

> It's funny how useful water is for power generation.

It's gravity that does the generation. Water is convenient because it's weight per unit of volume is very high. Higher than most things we can get our hands on and it's also exceptionally safe.

Since water isn't perfectly clean the main problem you face is corrosion. Which can take a great system and turn it into a nightmare of buried leaks and sudden problems.

As far as our options go it _is_ really convenient.

by themafia

2/3/2026 at 1:34:02 PM

And maybe it's obvious, but the largest thing that makes water so useful is that on our planet it's usually liquid but has easy to reach boiling and freezing points. Most notably a boiling point that is easily withstood by most metals and trivially reached by most methods of heating. Chemically something like quartz would work just fine, but its heating and boiling point are way too high to be practical. Occasionally we do reach for molten salts like lithium chloride

by wongarsu

2/2/2026 at 10:40:18 AM

Indeed.

In the UK there was a unfortunate trend of ripping out these energy storage devices and replacing hot water tanks with on demand electric hot water heating ( only heat the water you need ). And new builds often have no tanks ( as it saves space in the new tiny homes ).

Very short sighted in my view - a very simple way to store energy and everyone uses hot water directly.

by DrScientist

2/2/2026 at 10:58:16 PM

They don't work well with heat pumps. Heat pumps lose efficiency as the differential increases, so if you try to store heat in a tank, you quickly drop capacity and efficiency.

Versus resistance, which is exactly as efficient at 0°C and 1000°C, and why those storage heaters used to make sense.

(And storage is directly proportional to temperature differential above interior ambient)

by coryrc

2/3/2026 at 11:54:12 AM

Every air-to-water heat pump install will have a hot water tank. So I'm not sure why "don't work well" is the term used.

It is true that heat pumps coefficient of performance drops as the output temperature increases. So you need a proportionally larger hot water tank to store the same amount of energy. So it is fair to say there are tradeoffs. But hot water storage is still a necessary part of most heat pump installs - because peak output of heat pumps tends to be below the heat demand of showers.

by leoedin

2/4/2026 at 3:52:21 AM

EDIT: I misread "ripping out these energy storage devices" as https://en.wikipedia.org/wiki/Storage_heater which are basically bricks with nichrome wire.

You're right, of course heat pump water heaters use tanks to smooth out DHW demand, but that same thing isn't feasible for space heating.

by coryrc

2/3/2026 at 7:31:29 AM

Home hot water heating in the UK with heat pumps is about 250-300% efficient (slightly lower than the efficiency of home heating but still much better than resistive).

No one is storing 1000C water at home.

It is true that the temperature deltas affects efficiency. You can use the thermocline to draw from the cooler lower portion of the storage tank to push this further. Or less technically, just a bigger tank, though this has some tradeoffs.

In warmer countries they are set up differently can act as free air conditioning by extracting heat from indoor air at the same time as heating water.

by ZeroGravitas

2/4/2026 at 4:01:29 AM

> No one is storing 1000C water at home.

Right, but UK has/had "storage heaters" which were bricks with nichrome wire. They would heat the bricks really hot during cheap electricity times, and use that heat the rest of the day.

EDIT: I misread "ripping out these energy storage devices" as https://en.wikipedia.org/wiki/Storage_heater

Of course heat pumps for DHW should all have a tank for smoothing demand across several hours.

by coryrc

2/3/2026 at 9:49:25 AM

Isn't it better to heat the water up to a point (let's say 40 or 50 degrees) and to heat it the rest of the way with resistance heating?

>Versus resistance, which is exactly as efficient at 0°C and 1000°C

It isn't. The difference is smaller than for a heatpump tho obviously.

by modo_mario

2/4/2026 at 3:58:22 AM

1. No, absolutely not. Why would you settle for COP=1 when you can have COP>1?

2. The electrical to heat conversion efficiency is indeed 100% regardless of the temperature of the resistor. And if you're putting out 1000W, then all input losses are also identical. If you put a 1000W light bulb in the middle of your room, or 2 of them but run both at 500W, you'll get EXACTLY the same heat output in your room, but the single bulb is much hotter.

by coryrc

2/3/2026 at 12:51:26 PM

Older heat pumps had max temperature limits and did often have resistance heaters to get that last push above 60C. Modern household heat pumps will reach 75C while staying above 100% efficient and can skip the resistance heater.

This is partly due to a change in the refrigerant used.

by ZeroGravitas

2/3/2026 at 1:21:45 PM

> Modern household heat pumps will reach 75C while staying above 100% efficient and can skip the resistance heater.

Is this adequately maintained even as temperatures drop? I was recently considering getting a heatpump in addition to my gas installation but I assume I need to go for more than a bit better than resistance heating during winter for that investment to make sense.

by modo_mario

2/3/2026 at 11:54:58 AM

> It isn't. The difference is smaller than for a heatpump tho obviously.

Where does the energy go then?

by leoedin

2/3/2026 at 1:19:28 PM

It mostly leaks and such. Limescale buildup is also a small issue for their efficiency and more so if they run hot. If we reduced it to a simple input output calculation that would never be an issue except for some speed of transfer.

by modo_mario

2/2/2026 at 8:48:18 PM

My hot water tank once fell off the wall. On Christmas day. Expensive repair.

Hot water tank was in the basement, which was not insulated. So the mass of hot water contributed very little as a heat reserve for the house.

House was in a northern clime.

by a_better_world

2/2/2026 at 10:52:16 PM

Those are great for buffering only a few hours though. That would help avoid the expensive electricity price peaks.

by manmal

2/2/2026 at 8:47:58 PM

it also reduces peak load - you can heat water up slower with a lower powered heater. I have a 35 liter warm water tank in my garden shed that pulls about 3.5kw - an equivalent on demand heater would need 14kw or more.

by Xylakant

2/3/2026 at 7:42:39 AM

I don't see why that matters. You use the same amount of energy and the demand is smoothed out at grid scale (yes I know about tea in ad breaks).

by IshKebab

2/3/2026 at 11:51:00 AM

You can get things like cheaper overnight tariffs when the demand is lower - if you have some sort of storage system - like a hot water tank - in effect the electricity company is distributing some of that smoothing function to things like hot water tanks, storage heaters or batteries.

If you have your own solar ( either direct solar water heating, or solar electricity generation ), the hot water tank is a simple, cheap, reliable energy store.

Sure capacity isn't that great - but pretty much every house in the UK used to have one, so it adds up.

by DrScientist

2/3/2026 at 7:59:30 AM

Houses in the UK typically have 100A supply and the whole local grid is sized assuming people use relatively small amounts of electricity. If everyone gets an electric car and a massive heat pump, lots of local transmission will need upgrading

by ifwinterco

2/3/2026 at 12:18:01 PM

Right but unless everyone is drawing large amounts of power at the same time it doesn't matter if you use 1kW for 10 hours or 10kW for 1 hour. To the grid they look the same.

One interesting case where "at the same time" actually does happen is overnight car charging. Some chargers are configured to start charging exactly when a cheaper tariff kicks in, which causes big transient issues for the grid. I think modern chargers have a random delay to help with that.

by IshKebab

2/3/2026 at 8:04:35 PM

Yep but while that is true at the level of the overall grid, actually the nearest part of "the grid" might be a local transformer that only serves 10-100 houses.

At that scale, it's definitely possible that you all plug in your electric cars and turn on your heat pumps more or less at once on a cold evening after work and start cooking your local transformer. Not my day job but I think it is a potential issue when everything is sized assuming ~2kW average demand or something

by ifwinterco

2/3/2026 at 2:11:43 PM

> Some chargers are configured to start charging exactly when a cheaper tariff kicks in, which causes big transient issues for the grid. I think modern chargers have a random delay to help with that.

Here in the UK some electricity providers offer 'smart' charging (e.g. Octopus Intelligent Go).

In that situation the energy provider controls when to charge the car - e.g. you say "I want the car at 80% by 7am tomorrow" and the energy provider controls the timing of charges.

That's how my EV charges - I plug it in, and Octopus control it.

Benefit for me is that whenever the car is charging my entire home's use gets the overnight rate (even if part of the schedule is charged during the day).

Benefit for Octopus is they can use my car to balance grid demand / schedule the charge when it is most financially effective for them.

I can - at any time - override that logic if I just want it to charge at a specific time for whatever reason.

(I presume this sort of arrangement is becoming more common in other countries too)

by footydude

2/3/2026 at 3:08:20 PM

I think the advantage is that hot water loses heat over time, depending on how good the insulation is. However with phase change materials, the heat is trappped in the phase change and is stable until you release it.

by shellfishgene

2/2/2026 at 12:06:26 AM

This is similar to nighthawkinlight's videos on phase change materials. It was very cool to see how his Ziploc bags of homemade goo helped regulate temperature.

by Neywiny

2/2/2026 at 6:26:54 AM

In this work the authors use a ceramic-coated extruded aluminum heat spreader to improve thermal conductivity through the bulk PCM, but I wonder if the graphite flake+powder additive demonstrated recently by Tech Ingredients[1] would be a viable alternative? It might need a stabilizer (thickener) to prevent the ingredients from separating.

[1] https://www.youtube.com/watch?v=s-41UF02vrU

by schiffern

2/2/2026 at 8:48:13 PM

I've been keeping an eye on heat pump water heaters for awhile, but right now they mostly make sense in warm climates. The big problem is they're still specialty products and marked up like crazy, but also they tend to use cheap components which makes them loud and prone to failure. If you run A/C for the majority of the year then they pay themselves back reasonably quick, barring early failure, but in colder climates they make your house work that much harder to keep the space warm.

The most optimistic hope is that the government mandate will force enough demand that manufacturers can enjoy some economies of scale and actually try to compete on price. I don't think this will happen anytime soon.

by jandrese

2/2/2026 at 8:52:48 PM

I had a heat pump installed in 2010. In a cold climate. Only used for heating. It paid for itself extremely quickly - less than three years. It's still going strong, in 2026. It's important to maintain it regularly, i.e. deep cleaning every two years or so. The first time I got a company to do it for me, and the technician taught me how to do it all by myself, so that's what I do. In any case having a professional doing it wasn't expensive either. And I clean the dust filters (very easy) every second week or so.

by Tor3

2/2/2026 at 9:50:11 PM

Installed mini-splits to replace the propane stove that heated my house, DIY job, so all it cost was the units themselves and some materials.

Propane bill (no natural gas, town of 500) from Oct 24 to Feb 25 (installed the mini splits that month) was $1200, for just heating.

My mini-splits are on a dedicated sub panel with an Emporia Vue 3 energy monitor. $604 in electricity consumption, and that includes air conditioning over the summer months.

For what it’s worth, our winter weather averages 25-35F with the occasional few days dipping to tens, single digits, and the occasional -10 freak; but these units just BARELY have a HSPF4 rating to classify as “cold climate” models. Still going to pay for themselves in 6 years without any tax credits, and 4 or so since I still installed them when they were available.

by snuxoll

2/2/2026 at 9:16:25 PM

What did you heat with before?

by stuaxo

2/3/2026 at 7:26:02 AM

Electric resistive heating, which is the main power source here (all hydro, until recently). Plus a wood stove in case of power cuts. We used that one quite a bit during cold spells before the heatpump came along. Now not much at all.

by Tor3

2/2/2026 at 10:54:12 PM

Certainly not gas or oil, which are still cheaper to heat with than heat pumps.

by manmal

2/3/2026 at 2:07:14 AM

Modern heat pumps are cheaper than oil for heating just about everywhere. They're cheaper than natural gas in most places, unless electricity prices where you live are particularly high.

by tempestn

2/3/2026 at 11:40:43 AM

Yes, and many places have high electricity costs. And btw, those are hard to foresee, so if you make a long term investment into a heat pump that is supposed to last 20-25 years, you have no idea how electricity prices will affect you. That's obviously true for gas and oil as well. I do concede that my original point was too blanket-y.

I have a heat pump btw., with COP 4.5 (below ground). Costs me EUR 2.5 - 3k per year to heat the house.

by manmal

2/3/2026 at 3:59:48 AM

in CA my natural gas is far cheaper than the heat pump sadly

by zobzu

2/3/2026 at 8:44:26 AM

In western europe today, I spend €10+ per day to heat my home (17 degrees mind you) with a gas powered boiler for radiators. I can run my mini-split on 18 degrees all day for a couple of euros. I moved here from the US in 2022 right after the full scale invasion of Ukraine so natural gas prices skyrocketed overnight.

I don't really understand what the aversion is to forced air climate control here other than "it's not as comfortable" which from what I've gleaned from other people is taken to mean noise/moving air/humidity. Coming from the southern US, I find all of those points to be a non-issue for me. I've slept with a fan on my entire life, so if I can shave off 50% of my heating costs for a few decibels of fan noise, sign me up!

by yurishimo

2/3/2026 at 11:42:21 AM

I don't buy your numbers. I'm in Western Europe myself, and have run those numbers multiple times. Kilowatt for kilowatt (COP adjusted) gas is always cheaper than a heat pump.

by manmal

2/3/2026 at 7:27:49 AM

Hm? Around here oil was never been in the same (low) order of magnitude. Those who installed oil heaters many decades ago regretted it quickly. And it's been illegal to use them for a couple of decades as well now. Gas has never been an option in my region, there's no infrastructure for that. We have used gas in Japan until now, but even that we'll be phasing out (I live in two places)

by Tor3

2/3/2026 at 11:47:12 AM

> Those who installed oil heaters many decades ago regretted it quickly.

That really depends on the oil heater, no? You can't compare a heater from the 70s with a modern one. That's like saying I don't drive modern cars because cars in the 70s were unsafe and stank.

by manmal

2/3/2026 at 3:47:59 PM

Needing an oil tank, smell, expensive (oil price typically increased drastically compared to the beginning), pollution, and, as I said, made illegal in cities for various reasons, pollution and expenses related to dig up and get rid of the oil thank, and more.

by Tor3

2/3/2026 at 8:14:50 AM

I’m in Japan too. Could you name the model you ended up going with? My heating bill in the winter is insane.

by darkteflon

2/3/2026 at 8:38:35 AM

The model is not yet decided, we're in the finalizing stage with the building company. What we have been focusing on is a well insulated house, unlike the old one which has no insulation at all.. if we tried to heat that it would not only be extremely expensive, it's impossible to even heat the small bathroom with an electric heater. So instead you kind of get used to it. Took me a year to stop feeling like I was freezing, at 4C in the bathroom on February mornings. We have been using a gas heater (plug in the floor) in certain places on the ground floor, but we limited that as well. So, with an insulated, small house, we believe we will be able to keep the costs down, using heat pumps and heat exchangers, plus solar and battery (using the car battery).

by Tor3

2/3/2026 at 9:43:00 AM

Oil heating has usually been the most expensive way to heat in the UK, on par with resistive-electric.

by pjc50

2/2/2026 at 8:57:40 PM

I think a heat pump only for water isn't the right way to go. In the EU, new systems I see use a single heat pump for all heating and cooling in the house including heating water.

I do miss my natural gas on-demand water heater from when I lived in the states though. Unlimited hot water was nice, and it took up almost zero space.

by matwood

2/2/2026 at 9:35:13 PM

While they are not as efficient or flexible, they are many times more efficient than resistive electric water heaters. I've installed one with in house air intake (due to construction reasons) in my house and it cooled down the basement by a few degrees (and removed air moisture as an added bonus). In summer the thermal capacity of the ground heats up the basement again, in winter it's a bit cooler, but it still works efficiently.

by luckystarr

2/3/2026 at 3:43:42 PM

They are efficiënt but all that efficiency is eaten up by electricity being more expensive than gas.

by LunaSea

2/2/2026 at 9:05:54 PM

Which models are you looking at? I was still quoted separate pumps for floor heating and a boiler with the pump built in taking the energy from the air two years ago.

Is it something from nefit by any chance?

by spockz

2/2/2026 at 9:22:15 PM

This is promising.

https://www.pv-magazine.com/2026/01/29/samsung-releases-new-...

> The South Korean giant [Samsung] said its new EHS All-in-One provides air heating and cooling, floor heating, and hot water from a single outdoor unit. It can supply hot water up to 65 C in below-zero weather.

> Dubbed EHS All-in-One, the system provides air heating and cooling, floor heating, and hot water from a single outdoor unit. It is initially released for the European market, with a Korean rollout expected within a year. “It delivers stable performance across diverse weather conditions. It can supply hot water up to 65 C even in below-zero weather and is designed to operate heating even in severe cold down to -25 C,” the company said in a statement. “The system also uses the R32 refrigerant, which has a substantially lower impact on global warming compared with the older R410A refrigerant.”

by toomuchtodo

2/2/2026 at 9:09:48 PM

Afaik heat-pumps in the EU can provide unlimited hot water–what am I missing?

by thunfischbrot

2/2/2026 at 9:28:13 PM

Geothermal (and airbased) pumps theoretically do not have unlimited heating capacity. For example my pump (Daikin Altherma Geo 3) has a 180 litre water tank so it can ”only” supply 180 litres hot water at 65 degrees Celsius and takes about a minute to heat two additional lites.

So if I want to quickly scald myself in a 400 litre pool at fifty degrees I can’t. But if I had a gas heater that would be possible!

by Y-bar

2/3/2026 at 2:03:35 AM

Depends on how you measure unlimited. My hot water heater can pretty much indefinitely supply hot water for a single shower head with a modern water saving design. It can heat faster than 1.2 gallons/minute

by malfist

2/3/2026 at 8:49:42 AM

> I do miss my natural gas on-demand water heater from when I lived in the states though.

Isn't that what we call a combi boiler in the UK (and Europe?) I've recently moved from having a big hot water cylinder to a combi. The space saving is nice, but there are downsides.

Waiting for the hot water to come through is annoying and I'm often just wasting cold water waiting for it to come through hot. There is a "pre-heat" feature which would be nice, but then it would keep it warm 24 hours a day which is ridiculous. Maybe some better boilers can time the pre-heat. That would probably be close to perfect.

The other downside is it can only really supply one tap with hot water. So if someone is having a shower and someone else runs a hot tap it can be unpleasant. Requires some coordination between householders.

All in all I would definitely prefer a cylinder if I could afford the space it takes. Modern cylinders are incredibly efficient. I once turned the heating off for a week while away on holiday and when I came back the water from the cylinder was still tepid.

by globular-toast

2/3/2026 at 9:09:03 AM

> There is a "pre-heat" feature which would be nice, but then it would keep it warm 24 hours a day which is ridiculous. Maybe some better boilers can time the pre-heat.

Yeah one of my colleagues has a preheat which can be triggered manually and via automation. They also have a preheat loop which cycles hot water through the entire piping as the boiler is on an edge, so it takes ages for hot water to reach the far bathroom.

by masklinn

2/2/2026 at 9:47:53 PM

You're about 20 years behind.

My heat pump is working great at 0F. It's 7 years old.

by gwbas1c

2/3/2026 at 6:13:42 AM

It really depends on how well your home is insulated. Heat pumps don’t work well on old, poorly insulated houses in cold climates. If they can keep up, which is a big if, the price of electricity generally dwarfs natural gas, even if the heat pump is running at 250-300% efficiency.

by hippo22

2/3/2026 at 2:24:07 PM

> Heat pumps don’t work well on old, poorly insulated houses in cold climates. If they can keep up, which is a big if, the price of electricity generally dwarfs natural gas, even if the heat pump is running at 250-300% efficiency.

I've got a 1930s semi-detached house (UK, north of England) - heated solely by a ASHP for both heating and hot water.

Our Seasonal Coefficient of Performance is currently 3.47 (347% efficient) - even if limit that to just last month (coldest month of the winter so far in the UK) our COP was 3.25 (325% efficiency).

Roughly speaking if you can achieve a COP over 3.2x in the UK it should be roughly on a par with gas, assuming you go 'gas free' (i.e. you can make the saving on the gas standing charge).

Personally we're running at ~£200 annual saving vs. my estimate of what costs would be for equivalent gas boiler - that's thanks in part to being able to do all our hot-water heating at night rates.

House wise - we don't have cavity wall insulation, have 15+ year old double-glazing and probably should have more insulation in the loft (it fills the rafters but I think these days that's considered not enough).

Also with changes to ECO (energy company obligations) and RO (renewables obligations) the differential between gas and electric will reduce further

Anyhoo - added my example to show that ASHP can work perfectly fine in old, poorly insulated homes in (moderately) cold climates.

ECO/RO link - https://www.moneysavingexpert.com/news/2025/11/energy-bill-c...

by footydude

2/3/2026 at 6:19:57 PM

The issue with poorly insulated houses in cold climates is not about efficiency. The issue is that the thaw cycle makes it impossible to actually come up to temp because too much heat is lost during thawing. Most of the UK isn’t really considered “cold”, which is probably why you don’t have this issue.

by hippo22

2/3/2026 at 7:39:10 AM

It's not really correct to say that heat pumps don't work well on old, poorly insulated houses in cold climates. That it's a heat pump is not the issue, that it's cold is not the issue, the problem is only that with poor or no insulation in a cold climate you'll need a huge heater (say, 10-15kW just for the living room). And domestic heat pumps are not designed for that range. If you could get one that big then it would work very well indeed.

If you have a poorly insulated house then the fix is to insulate it, which is what a lot of people are doing around here, with very hold houses. My house is less than 60 years old and very well insulated for the time, and it holds up even today - it's always warm, with the heat pump not even close to its max power.

by Tor3

2/3/2026 at 7:21:13 PM

The issue with “just” insulating your home is that many homes weren’t designed with insulation in mind and thus it’s not a straightforward proposition.

For instance, masonry was a common building material and that is not easy to insulate. You need to add many inches of insulation on either the outside or the inside, both of which have complications.

Even in a basic stick framed house, you’re still talking about taking down all the exterior walls, likely involving removing plaster and replacing it with drywall. Plaster has a number of nice properties, so it’s sad to remove. And that’s not to mention the price of this work.

Finally, roofs need special consideration. Most roofs today need to be properly vented, which was not as much of a consideration when the houses naturally breathed. Venting today is often done with soffit vents. Yet on historic houses, soffits are typically one of the nicer details. It’s not trivial or cheap to install venting in such cases.

by hippo22

2/3/2026 at 3:49:33 PM

> If you have a poorly insulated house then the fix is to insulate it

I've been quoted prices to insulate my house that represent 50% of the original acquisition price of the house.

I would need to pay 0€ for both electricity and heating for the next 100 years for this to make sense at current prices.

by LunaSea

2/3/2026 at 10:46:13 AM

To clarify my parent post: My house is also 7 (now 8) years old and has 6 inch (15cm) walls with air-tight walls. We built with solar, which got the cost of electricity down to an estimated 4-5 cents per kilowatt hour.

At that price, resistive heating cost about as much as what I paid for gas at my old house.

I went with a heat pump to hedge the bet. (I was also pointed away from geothermal.)

If the insulation wasn't as good, or electricity more expensive, I would have used a different heat source. I was looking at pellet furnaces at the time, but never seriously got into the research before the solar proposal came in.

by gwbas1c

2/2/2026 at 9:52:51 PM

heat pump for house !== heat pump for hot water

by baggachipz

2/2/2026 at 10:21:29 PM

I don't know what it's like where you're living but here in Switzerland it's completely normal to have one heat pump that does both. Here there's a lot of floor heating, which also uses water, so you usually just run one loop to the "boiler" (a water tank with a copper loop for the water from the heat pump to circulate through) and one through the floor and have a valve to switch which is running through the heat pump.

I have one of these: https://cta.ch/en/private/products/ah-i-eco-innen

I got it in October so most of the time I've had it has been <10C. It's produced 806.3 kWh of heating for hot water and 6587.2 kWh for the floor heating. It consumed 302.7 kWh and 1801.4 kWh respectively, for a COP of 2.66 and 3.66.

by Youden

2/3/2026 at 8:10:04 PM

That's a different kettle of fish entirely, largely because with the heat pump water heater they're pulling the heat from the inside of your house, forcing you to move it twice when it is cold out. With a combined unit you only move it once, as the other side of the unit is outside.

That's why they're so great for warm climates though. The water heater also cools your house, especially as that heat is then lost down the drain. Everybody in the south should be jumping on these.

by jandrese

2/2/2026 at 10:51:25 PM

There's a lot of different heating systems: If your heating system uses hot water at any point, (baseboards, hydro-air, underfloor, ect,) using a single heat pump makes a LOT of sense.

Personally, I prefer an air-source heat pump hot water tank. It significantly dehumidifies my basement.

by gwbas1c

2/3/2026 at 5:25:28 AM

Yes, same thing. Heat pump to heat exchanger. This is over 39 years old tech and in common use around Scandinavia and mainland europe. This is ancient technology.

by serpix

2/2/2026 at 10:19:46 PM

Why not?

by karussell

2/3/2026 at 5:31:40 AM

Mine are in climate zone 6. They're only a couple years old. The coldest temperatures I've run them at so far are -21°F and they kept the house adequately unfrozen. They'll maintain a COP of 2 down to 5°F IIRC. The hot water heater is an 80gal Rheem heat pump unit. No complaints there either. It would be pretty great to have some thermal storage though, temperatures in the dead of winter here are usually above 5°F during the day but drop well below zero at night. Blasting the heat pumps during the day to bank heat for overnight would be far more efficient.

by jcgrillo

2/3/2026 at 1:07:17 AM

They marketing like it's an expensive tech, but it's pretty cheap.

We have been buying heat pump PTAC for the hotels for last 20 years, and price difference is usually 5% between with and without heat pump.

Seems like all companies are colluding with each other for marking up prices.

by newhotelowner

2/3/2026 at 2:01:47 AM

We somewhat accidentally ended up with a good combo: we have a ventless heat pump dryer, and a heat pump water heater, also in the laundry room. So when doing laundry, the water heater cools the room while the dryer heats it, so they roughly cancel out.

As an aside, HP dryers are really elegant tech, and it's a shame they're not more common. They use the heat pump not just to heat the air in the dryer, but also to condense the moisture back out of it, so just the water can be drained away instead of needing to exhaust the air outside. So you need much less energy overall, and you don't need a dryer vent. The only downside is they're a bit slower, but ours has a resistive backup option for when you need clothes dry asap, so really it's just price.

by tempestn

2/3/2026 at 2:15:21 AM

Heat pump dryers work at a much lower heat as well since much of the heating of a traditional dryer is lost out of the vent. The heat pump condenses the water out of the hot air so you don't lose the heat.

I've stopped needing to sort my clothes out as a result, I used to hate putting synthetics in a regular dryer because they get worn out so fast that way.

by zhivota

2/3/2026 at 2:26:46 AM

I bought a Samsung HP dryer a few years ago and it'd be great except for a terrible design flaw where lint gets trapped in its heat sink fins, turning into a soggy mess.

by jonstewart

2/3/2026 at 3:46:51 AM

We have a Whirlpool that I love, but they discontinued it a couple years ago with no replacement, and I can't imagine why. I guess most people just shop on price, so it didn't sell. Like I said, a shame.

by tempestn

2/2/2026 at 9:14:49 PM

They use them a lot in Norway, it's hardly warm there.

by stuaxo

2/2/2026 at 9:42:19 PM

I'm in the northern US and am very happy with mine. I self-installed with a county rebate, so the total cost was a Saturday and $700. My old electric unit was EPA rated for $450/year, and the new one has averaged $170/year over 4 years, so I've already broken even.

by ortusdux

2/2/2026 at 10:14:52 PM

> government mandate will force enough demand that manufacturers can enjoy some economies of scale

So you want the government to pick winners and you want to do business with a monopoly? This is the opposite of what you would want.

If the product saves me money, and it's _actually_ better, I will buy it in a heartbeat. If you're involving the government it's because one of those things isn't true.

by themafia

2/3/2026 at 5:13:52 AM

Gas infrastructure is expensive to build and maintain. Often times with tax money. What tend to happen in Europe is that they phase out gas by not building gas lines for new development.

by enaaem

2/2/2026 at 9:47:19 PM

I was interested to learn about cold district heating recently, which is basically a municipal scale geothermal system.

https://en.wikipedia.org/wiki/Cold_district_heating

by ortusdux

2/3/2026 at 12:20:05 AM

I went to Moscow in December several years ago and learned they've got one the world's largest district heating systems.

by yowayb

2/3/2026 at 1:26:09 AM

I am not sure if this is still the case, but up to 20 years ago, these were typically shut off in May-June to August for “maintenance” which resulted in a prolonged period of no hot water in apartments.

by xattt

2/3/2026 at 5:34:53 AM

In Moscow? Never. It's been usually a month in soviet times, two weeks max nowadays, usually sometime in late June - early August.

edit: also on heating question - Moscow's electricity is provided by 40 or so big gas-fired steam turbine generator plants, about 10GWe total. District heating serves as cooling for all this power generation.

by lstodd

2/1/2026 at 10:14:00 PM

I would love to see a bus-sized version for year-long temperature moderation. Like, drop house heat into it during the summer so it can re-heat the house over the winter, and pull all the heat out of it by Spring so that it can cool the house over the summer.

Bus sized because that amount of thermal mass is bound to take up a lot of space, but capable of being buried so that it doesn’t actually take up property space.

by rekabis

2/2/2026 at 2:54:18 AM

I ran the numbers for this a while ago. I live where we have proper winters (currently -22c). I wanted something simple just with solar thermal and water pumps (no heat pump). Sand batteries work at an industrial level, but for domestic use you want something simple so that means just water.

A 100m3 (100,000 litres or 26,500 gallons) cylindrical water tank (approx 5x5m) buried and insulated with 50cm of XPS could provide around 4000kWh of deliverable heat throughout winter. Which would be more than enough for heating and domestic hot water for my house.

In the summer you'd use solar thermal to charge it to 85c. In the winter you'd run water through underfloor heating and discharge it to 35c (so you just need a mixer valve and pump).

The structural engineering part of it isn't actually that complicated (with a garden on top, not a house). You can buy plastic water tanks of that size, it just needs to be buried and have XPS foam placed around it.

Because it's volume, it scales up well. An extra one meter in each direction would increase the volume by around 60%, but you have a lower overall heat loss, so the heat capacity would more than double.

The important part of it is the XPS foam though, without this the loses are too great and you don't retain any heat. This is why insulating your foundation and slab is so effective.

by fy20

2/2/2026 at 6:50:11 AM

So… store heat in an insulated swimming pool 10ft deep, 30ft wide, and 90ft long, at 185F, above the service temp for XPS foam, got it, ok. At least you could also use it to sous vide an entire cow.

by bilbo-b-baggins

2/2/2026 at 5:14:54 AM

Interesting practical approach to actual build it. Did you do a cost analyses or RoI?

by eande

2/2/2026 at 5:29:10 PM

Pedantic Pete here:

  • The centigrade is capitalized when used after a number. There is also a singular glyph for the entire degree-centigrade convention: ℃.

  • There are also superscript numerical characters to use with volumes, without having to use formatting: m³.
UTF-8 is fun! As is automatic text replacement, once you have the appropriate triggers set up.

by rekabis

2/3/2026 at 1:15:44 PM

The use of unit characters in Unicode is not recommended by the consortium, they mostly exist for compatibility with Asian encodings. The recommendation is to use the Latin letter and the degree sign.

See page 758 of the Chapter 22 for the Unicode 9.0 standard:

https://www.unicode.org/versions/Unicode9.0.0/ch22.pdf

by tecleandor

2/2/2026 at 9:01:16 PM

This exists, in german it's called Eisspeicherheizung. You have a few cubic meters of water buried in a concrete bunker and you use a heat pump to pull energy out of the water until it freezes. The system not only uses the thermal mass of the water, but the thawing/freezing energy which is higher than the energy required to heat water by 1degree by a factor of 80 - meaning if you freeze 1kg of water, you need to pull out enough energy to heat one kg of water by 80 degrees.

You can then use a heat pump that's optimized for the expected temperature range and you don't even need to insulate your water storage tank - you actually want the cold in winter to seep out into the surrounding soil, free energy.

In summer you have cold storage for your AC.

by Xylakant

2/1/2026 at 11:37:32 PM

So…geothermal? I wish this was possible too but I don’t see how it will work scientifically. Water is one of the chemicals that have one of the highest thermal mass/specific heat (maybe 1/3 of salt hydrates). Even then, you have to bury a crapton of water underground. This design mentioned in the article is more for short term, like 12 hours storage (since they’re accommodating for solar in nighttime)

by syntaxing

2/2/2026 at 12:00:33 AM

Is geothermal not the opposite of that? My understanding was that the geothermal MO is that there's virtually infinite thermal mass in the earth so it won't heat/cool, not that you heat/cool your local chunk

by Neywiny

2/2/2026 at 12:05:35 AM

To a certain extent, yes. The reason why the water is there is because the thermal flux of the ground is low, so the large mass of water provides a strong buffer. But you can’t cheap physics. You would need a crap ton of salt hydrate to accommodate a whole season of heat needs, even if you don’t factor in thermal loss from the container.

by syntaxing

2/2/2026 at 5:19:05 PM

Geothermal needs either a horrifically expensive vertical bore hole going down a few hundred metres, or a good acre of land for laid-down piping. I have neither the money nor the horizontal space. So I am thinking something compact that needs to go only about 6-10m vertically into the ground (so I can hide it fully underground with about a metre of soil on top), and take up the horizontal space of 4 parked cars. I have more than enough room and cash to have that cube of space dug out.

And being on an alluvial plain, if I filter out all the rocks larger than a pea, a good 90+% of what is dug out can immediately be trucked away.

by rekabis

2/3/2026 at 4:08:02 AM

Yeah I always wondered if I ever switched to solar panels, would there be a way to accumulate heat to be used in the Canadian cold months that have little sunlight? The closest I found was electric thermal storage based on heating bricks. They can accumulate more energy than water since they can go to higher temperatures. For example these say they go to 1300°F or 700°C https://steffes.com/ets/roomheater/ . They don't seem to have large models that could heat a house for months however.

by BenoitEssiambre

2/2/2026 at 9:36:39 PM

I live in a climate where, for most of the year, the daily high-low temperature range includes 20C, so I'd like a whatever sized one is needed to average that out, and run most of the year without any active heating or cooling.

by aidenn0

2/2/2026 at 12:37:42 AM

You seem to be describing ground sourced heat pumps. If you wanted, you could insulate a a chunk of foundation or earth to avoid heat loss. But just the ground under your building seems to work well enough.

by stubish

2/2/2026 at 5:16:22 PM

Ground sourced heat pumps need either a horrifically expensive vertical bore hole going down a few hundred metres, or a good acre of land for laid-down piping. I have neither the money nor the horizontal space. So I am thinking something compact that needs to go only about 6-10m vertically into the ground (so I can hide it fully underground with about a metre of soil on top), and take up the horizontal space of 4 parked cars. I have more than enough room and cash to have that cube of space dug out.

And being on an alluvial plain, if I filter out all the rocks larger than a pea, a good 90+% of what is dug out can immediately be trucked away.

by rekabis

2/2/2026 at 10:20:56 PM

Not many numbers in there. I would be interested in some measure of energy and effect per volume, e.g how many kWh of heat are we talking about at e.g 1 liter, and how fast (kW) can it produce it?

by Epa095

2/2/2026 at 10:17:22 PM

The article omits some critical details:

It says this is both a "heat pump" and also "storage" AND says that it will run when electricity is cheap or plentiful. Thus:

1: Where does it pump the heat from? (Or is this not really a "heat pump" and instead is using resistive heating?)

2: How long does it store heat? Is this something that will store heat on a 24-48 hour basis, or will this store heat during the spring / fall when longer days mean extra power from residential solar, and then use the heat in the winter?

3: Is the unit itself "warm" when storing heat? Or is the heat stored in a purely chemical way and needs to run through a catalyst or similar to get it back?

4: Can this be scaled up for general domestic heating?

---

Just an FYI: There are plenty of schemes with resistive electric water tanks to store heat when power is cheap.

by gwbas1c

2/2/2026 at 10:35:19 PM

I would guess that is intended for a daily cycle, perhaps using air source heat pumps at times of day when the air temperatures are higher and electricity prices are lower, then using it as required.

As it works on phase change (e.g. think of melting ice) heat is added (or removed) without changing the temperature of the store (which, I guess, might be hotter or colder than where the heat is extracted or used).

by mike-the-mikado

2/3/2026 at 3:14:39 AM

But how hot does the heat source have to be?

Depending on the needs, resistive heating can get hundreds of degrees hot, but the best heat pumps that I know of can only raise the temperature about 60 or 70° f.

by gwbas1c

2/3/2026 at 9:05:16 AM

That's the whole point of this, no? Heat pumps can't heat up a large amount of water quickly (like resistive heating can). So if you have a solar peak at noon, where either yourself are producing cheap solar, or there's cheap solar on the grid in general, then you want to use that cheap energy to store heat for later use (like showers in the evening/morning).

So the way I see it, is that this material should be able to quickly store heat with the using the low temperatures that heat pumps provide, and be able to store it with minimal losses until it is needed.

by jcattle

2/3/2026 at 10:32:48 AM

> Heat pumps can't heat up a large amount of water quickly

No, it's about temperature difference. My heat pump water tank heats about as quickly as resistive water tanks; but it could never heat to hundreds of degrees.

by gwbas1c

2/3/2026 at 2:41:04 AM

Presumably it's air source and if it's indoors it will just be the air in whatever room it's in. That's how my ventless dryer works. I'm not sure what the implications are for taking heat from air that may have been heated by another heat pump are for efficiency. But also if it's summertime, they may be relieving load from your air conditioner.

by tootie

2/3/2026 at 10:35:42 AM

> That's how my ventless dryer works.

Do you mean a heat pump dryer? Those aren't taking heat from the room; they work by sending the air inside the unit through a powerful dehumidifier. (I have one, it's very nice.)

by gwbas1c

2/4/2026 at 12:23:39 AM

A dehumidifier is the same thing as an air conditioner. The coolant coils are still just exposed to the ambient air in the room. The same way a window air conditioner drips moisture, the dryer is like a backwards air conditioner that blows cold air into the room and hot air into the drum and condensed water drips down the drain. I suppose it ultimately doesn't matter once you open the dryer door and everything mixes together.

by tootie

2/4/2026 at 1:50:12 AM

My heat pump dryer does not blow cold air into the room. (My heat pump water heater does.)

The air inside the dryer is cycled through a dehumidifier and then the water is pumped out into a drain. This is in contrast to a typical US dryer that just blows hot air into the drum and then out a tube outside. Apparently most of the world doesn't do it like we do.

by gwbas1c

2/2/2026 at 10:35:51 PM

1. The device is just storage. It would be paired with an air or ground source heat pump.

2. With good insulation you can easily store heat for a day which is all you need. You're never going to get close to storing summer heat for the winter. That's not impossible but not feasible for something this scale (and not cost effective at any scale).

3. You just heat it up and cool it down. There are no fancy chemical processes happening other than the phase change. It's exactly like a phase change hot/cold pack you can buy on Amazon.

4. I'm pretty sure this is designed for domestic heating...

It's kind of an obvious idea tbh. I don't think they've done anything super innovative... They made an aluminium heat sink..

by IshKebab

2/3/2026 at 4:46:12 AM

> With good insulation you can easily store heat for a day which is all you need. You're never going to get close to storing summer heat for the winter. That's not impossible but not feasible for something this scale (and not cost effective at any scale).

This is ground basically. How deep varies but few meters underground you basically have average yearly temperature. You could pump heat from house to the ground to take it out from the ground during winter.

by npodbielski

2/2/2026 at 10:49:01 PM

the only new thing- no matter how they do it- is putting it on residential instead of commercial or industrial installs.

my childhood public school took us to some big commercial building- I think it was Sears' HQ- and they proudly showed us the huge blocks of ice providing chill during the day.

by butvacuum

2/3/2026 at 4:52:16 PM

An 85% round-trip efficiency and 4X smaller volume sound great, but how does the installed cost compare to just oversizing a hot water tank or running the heat pump harder during off-peak hours?

by BrtByte

2/3/2026 at 5:25:18 PM

That’s essentially what they’re doing. The innovation is an engineered material having a specified temperature of phase change.

So the temperature swing is smaller (almost zero) so heat losses due to non-infinite insulation are reduced.

by labcomputer

2/2/2026 at 12:41:29 AM

Starting to get more optimistic about our energy future. Things seem to be tracking pretty good

by Havoc

2/2/2026 at 12:51:54 AM

I wonder if this can store any heat or just heat pump heat. If it can store any heat, it would help a lot to further reduce heating costs in our modern energy efficient house.

Sometimes, in the winter, we get too much solar forcing, so if we don’t heat all, it can be 85F in the day in the house, but 60-65 at night. (We open the windows during the day, and don’t always close them at exactly the right time at night.)

by hedora

2/2/2026 at 10:28:28 PM

I think this can work and instead of that the heatpump pumps the heat into your house (when "solar is plenty") it would pump it into the storage. (I have a similar setup, but heat the water but of course this is rather limited)

unrelated: a simple technical solution to your window problem would be home assistant and a few sensors to notify you when the windows are open too long or open when too cold inside.

by karussell

2/3/2026 at 12:10:10 AM

It’s more about predictive modeling: At what time + temperature do you close windows, given predicted cloud cover and overnight temperatures/wind?

Come to think of it, if we had a big salt slurry that transitioned at 72F in the floors, that would probably do the right thing. It’d create a step function making it hard to heat above 72, or cool below it.

I wonder how much density changes as these things transition. Would a static pool (mixed by freezing) work, or would it need a pump?

by hedora

2/3/2026 at 8:01:45 AM

It sounds like you need more thermal mass, a traditional brick/stone house wouldn't have that problem

by ifwinterco

2/2/2026 at 11:22:42 AM

Heat pump heat is just heat.

by direwolf20

2/3/2026 at 6:40:56 AM

I'm interested in storing cold, not heat

Storing cold during the night is probably more efficient

I thought about making ice blocks with a freezer on my balcony, probably not a good idea

by jokoon

2/2/2026 at 1:37:14 AM

Related, TIL the US is effectively banning residential electric resistance water heaters in 2029, with heat pump water heaters being the only type that can meet the new standards. Users will see a 2-3x in cost difference and a 3 to 8 year payback on savings.

by hnburnsy

2/2/2026 at 5:06:54 AM

This is exactly the kind of thing government is for, even though it's missing the other half: subsidies. At the very least buying heat pumps for the next 5 years should be tax deductible. Even better: a $2000 or similar rebate.

by amazingman

2/2/2026 at 11:43:21 AM

> even though it's missing the other half: subsidies

It's a double edged sword. In my country everyone bought pellet stoves because of the subsidies, hundreds of companies popped up, now that the subsidies have been phased out, 90% of the companies went down, with their support and warranties of course. The 10% that managed to survive increased their prices, which is easy to do once 90% of your competitors went bust

People who thought they'd save money by having the government (their taxes really) pay the bill are waking up 5 years later with expensive maintenance, the first units are starting to fail and need to be replaced but they can't afford it without the 50%+ subsidies. Not to mention that the prices pellets goes up and down faster than your average shitcoin.

by lm28469

2/2/2026 at 1:19:59 PM

The subsidies and rebates are a scam. The installers just jack up the prices until they capture the entire value of the rebate.

by rayiner

2/2/2026 at 4:58:37 PM

This assumes the consumer doesn't know and can't look up the price of the hardware.

by amazingman

2/2/2026 at 5:12:55 PM

The cost of installation vastly exceeds the cost of the hardware. And the installers will only warranty hardware you buy from them.

by rayiner

2/2/2026 at 5:20:34 AM

That's probably exactly what will happen.

    Energy property - Heat pumps and biomass stoves and boilers

    Heat pumps that meet or exceed the CEE highest efficiency tier, not including any advanced tier, in effect at the beginning of the year when the property is installed, and biomass stoves and boilers with a thermal efficiency rating of at least 75% qualify for a credit up to $2,000 per year. Costs may include labor for installation.

    Qualified property includes new:

    Electric or natural gas heat pumps
    Electric or natural gas heat pump water heaters
    Biomass stoves and boilers
https://www.irs.gov/credits-deductions/energy-efficient-home...

by DangitBobby

2/2/2026 at 5:36:42 AM

These are credits that only work if you have owe federal taxes and they cannot be carried forward. I've seen estimates that 40-45% of taxpayers owe 0 or close to 0.

by hnburnsy

2/2/2026 at 2:20:05 PM

You can also get considerable rebates if your state participates in the "Inflation Reduction Act Home Energy Rebate Program", especially if you are low income. My state is still working on rolling it out but hopefully many people who can't use tax credits will be able to take advantage.

https://www.tn.gov/environment/program-areas/energy/state-en...

by DangitBobby

2/2/2026 at 10:49:49 AM

Eh? If you have income you owe taxes, Uncle Sam just takes it before you even see it

by mrd999

2/2/2026 at 11:21:33 AM

Federal taxes specifically.

by direwolf20

2/2/2026 at 9:57:33 PM

I think something like 25% of the population reports 0 household income.

(I don't understand the implications, it was just surprising when I heard that.)

by JoblessWonder

2/2/2026 at 10:18:36 PM

The problem is, energy use is only one part of the equation. Often times new appliances that are more efficient end up being more prone to breaking due to more complexity and companies trying to cut costs to meet a price point. This leads to people needing to replace there appliances much more often which really makes me question how much energy is actually saved if you include the energy used to produce them...

by seiferteric

2/3/2026 at 2:39:59 PM

That seems like a stupid ban. Heat pump water heaters are impossible to install in many smaller dwellings, even if we're ignoring the need for large storage tanks.

The only problem with resistance heaters is the large current draw to heat water for bathing. Central heating can be done at lower temperatures (as is the case with heat pumps), but bathing cannot.

There are some resistance heaters with built in (electrochemical) batteries aimed at reducing peak current, but I'm assuming the ban would affect those as well...

by elric

2/2/2026 at 9:15:29 AM

I don't know about all heat pump systems, but mine at least requires the water tank to have a resistive immersion too. If the tank temperature gets below some threshold the heat pump refuses to work and turns the immersion on instead until it's warmed up enough.

by reorder9695

2/2/2026 at 2:14:07 AM

Is that 2-3x before or after the plumber marks it up?

What an exceptionally moronic thing to ban, the market solves this naturally. Resistance heaters are 100% efficient whatever fraction of the year is heating days. So if that's 1/2 the year and the water heater can't last 16yr because of water quality the heat pump heater will never pay you back.

This reminds me a lot of the time some jerks in west coast desert states convinced the feds to regulate plumbing fixtures so that eastern "we take from the river and put back in the river" municipalities that have more water than they know what to do with have to suffer through low flow everything.

by cucumber3732842

2/2/2026 at 1:54:54 PM

Heat pumps are effectively more than 100% efficient fyi. You put 1000W of electricity in, you get 2500W of heat going into the water. (Numbers are only illustrative)

Running cost of heat pumps for heating is much much lower than resistive heating.

by beAbU

2/2/2026 at 5:30:54 AM

Heat pump water heater (hybrid/HPWH, e.g., 50–65 gallon equivalent): Unit prices range from ~$1,500–$3,000+ (most common models $2,000–$2,500), with total installed costs $2,500–$5,000 (higher if electrical upgrades or space mods needed). Average retrofit/install often lands around $3,000–$4,000.

by hnburnsy

2/2/2026 at 11:30:36 AM

And for small households they virtually never pay for themselves before they die or need expensive maintenance... It only makes sense if you use a lot of water or if your electricity is very expensive. In my case it's even worse, with solar panels and self sufficiency they literally cannot break even

by lm28469

2/2/2026 at 7:07:24 AM

Electrical upgrades are almost always required, and price is more like 7k-9k around here. It's going to be seriously painful for a lot of people.

by sgc

2/2/2026 at 7:53:57 AM

If you were in the market for an resistive electric heat pump, you likely had the service for it already. A heat pump version will almost always require less power.

by dashundchen

2/2/2026 at 5:40:06 PM

My bad, read too quickly. I was thinking of the forced change over from gas water heaters, which is already happening in the California Bay Area and will only expand.

by sgc

2/2/2026 at 1:13:41 PM

If you currently have an electric resistive water heater, a heat pump water heater with the same heating capacity will use 3-4x less power, which means you can use a much smaller circuit.

A 6kW 240V EWH uses 25A, it’ll need #8 wire and a 35A or 40A breaker.

An equivalent HPHW would use 1.5kW at 240V, or 6.25A. You can use #14s and a 15A breaker.

by quickthrowman

2/2/2026 at 9:56:32 PM

Ehh 120v models exist. My 65 gal runs fine on a standard 20a breaker.

by drhike

2/2/2026 at 11:11:10 AM

Is the heat pump heater taking heat from inside or outside the house?

by direwolf20

2/2/2026 at 11:32:51 AM

Depends on the model, but a lot use the air from their own room, that's why they can't be installed in small rooms. Models pulling the heat from outside are more expensive and require more labor obviously, and they don't make a lot of sense for places that are bellow 0c multiple month a year as the COP will drop to 1.x and you will most likely need extra electricity for the anti frost cycles

by lm28469

2/2/2026 at 9:44:28 PM

But dumping the waste cold air into the house when it's below 0C outside doesn't make much sense either.

by AlexandrB

2/2/2026 at 11:35:01 PM

You already dump waste hot air into your kitchen from the refrigerator during the summer. Is this much different?

It does seem a little silly to have these chains of heat pumps all working in various directions. I read about "cold district heat" in a sibling comment which circulated lukewarm water to use as a heat sink or source with heat pumps. Maybe something similar could be done with a water or refrigerant loop through the house. Probably not economical to do all the plumbing though.

by wffurr

2/3/2026 at 12:59:44 AM

> you already dump waste hot air into your kitchen from the refrigerator during the summer. Is this much different?

Heating water is very energy intensive, fridges are a rounding error compared to water heaters

by lm28469

2/3/2026 at 11:33:35 AM

Everywhere in the country they have basements a huge fraction of them are unheated and probably hover around 38, 40, 35deg in the winter. You dump cold air into that and some % of pipes are going to freeze. And we're talking about a much bigger energy amount, water having high specific heat after all so it is a lot of "cold" being dumped in.

Now, this is of course no concern in the "my water heater is in my attic or attached garage" parts of the country such regulations come from...

by cucumber3732842

2/3/2026 at 12:06:14 AM

A hot water heater takes much more power than a fridge

by bethekidyouwant

2/2/2026 at 9:40:01 AM

[dead]

by aaaalone

2/2/2026 at 4:59:43 AM

That's a Biden-Harris administration action. What are the chances that Trump deletes it as a 'Democrat/WEF climate hoax con job' as soon as he's made aware of it?

by Sabinus

2/2/2026 at 2:21:42 AM

If you're making plans 3 years out in the US, you're a fool.

by pkulak

2/2/2026 at 9:39:28 PM

The problem with heat pumps replacing electric heaters (in cold climates) is that the waste cold air gets dumped into the house and needs to be heated again. Generally, electric water heaters are expensive to run compared to gas ones, so people use them in places a gas heater is not possible to install (e.g. no way to vent the exhaust). This also means that the heat pump would have nowhere to vent cold air.

This kind of thing is why I don't like bans like this. The specifics matter a lot.

by AlexandrB

2/3/2026 at 3:55:12 AM

Your heat pump ought to be venting the cold air outside in the first place. If you're pulling the heat for your water out of your conditioned air, yeah you're in a losing battle.

by grigri907

2/2/2026 at 12:12:09 AM

With the adoption of sodium batteries, I wouldn’t be surprised if solar panel + sodium battery would outperform this system by a lot.

by syntaxing

2/2/2026 at 1:46:10 AM

A heat pump gets more heat from a given amount of electricity than if the electricity is use for resistive heating. So the ideal design is solar cell + sodium battery + heat pump.

by belviewreview

2/3/2026 at 1:25:11 AM

Also when the temperature differential is lower, so ideal might be solar -> battery (to time shift to warmest outdoor temperature) -> heat pump -> thermal battery (to time shift to when you need heat).

Does seem like a lot of added complexity (and likely machinery cost) though.

by gpm

2/2/2026 at 10:58:06 PM

Even LFP batteries can work out better.

I live in Switzerland where these are available. A Cowa 58 [0] costs CHF 4692 [1] and stores up to 13.5kWh. If you're heating the water with a heat pump, that's ~6kWh of electricity, so ~CHF 782/kWh.

I'm in the process of installing a 33kWh battery and the battery + inverter cost CHF 13600 in total for just the hardware, so ~CHF 482/kWh.

If you add solar panels, the inverter does double-duty producing AC from both the battery and the panels. The battery does double-duty producing both hot water and allowing you to use solar energy outside the times when the sun is shining.

That said, having ordered a heat pump recently and being in the process of having solar + batteries installed, the amount of electrical work needed for the solar/battery install is substantially higher than was needed for the heat pump and here, the labour costs quite a lot, pushing the upfront cost difference even higher.

I think that's where these heat storage things fit in: they have a much lower upfront cost. No matter how cheap the battery, for it to be useful in a Swiss residence, it needs to output a substantial amount of 3-phase power (3-phase is standard here, even in most apartments), which means you need to spend a couple thousand Francs on an inverter and electrical work. These heat storage devices are quite cheap and don't even need someone qualified to handle refrigerants, I imagine they could be installed by a normal plumber.

That reduced upfront cost makes them far more accessible than electrical batteries, at least for now.

[0]: https://www.cowa-ts.com/uploads/files/Dokumente/Datenblaette...

[1]: https://nettoheizungshop.ch/Cowa-COMPACT-Cell-58

by Youden

2/2/2026 at 10:56:16 PM

Climates that need a hot tank of water to buffer for heat pumps, will not have meaningful solar panel output during winter. Or do you mean, just load the battery when electricity is cheap? A tank of water is 1k max, probably 10% of a sodium battery.

by manmal

2/2/2026 at 10:32:53 AM

There’s also solar thermal panels that heat up a liquid circulating in the system and cut out the need for a battery - and can just store the heated liquid.

by coffeebeqn

2/2/2026 at 8:44:53 PM

Efficiencies and effects are at the point where taking a photon, converting it into an electron, and using that electron to pump heat is more efficient than turning that photon perfectly into kinetic energy.

Similarly, in mild weather, it is more efficient to burn hydrocarbons and turn it into electricity to run a heat pump than use that hydrocarbon for it's heat energy directly.

Pumping heat is more efficient than making it.

by mrguyorama

2/2/2026 at 8:51:51 PM

Thermal solar panels have the advantage of being very simple and surprisingly effective. But if you're lacking space to put up both solar cells and thermal, you can use combined panels which have a solar cell with a backing thermal system. The interesting thing is that these combined panels outperform solar cells even when it comes to electricity generated because solar panels loose efficiency as they heat up, so cooling them actually improves efficieny. Combined panels are much more expensive, though.

by Xylakant

2/2/2026 at 10:37:08 PM

The problem with thermal solar panels is that you can use its heated water only if it gets warmer than the water in your system, which is not always the case, especially in winter.

Compared to nearly 100% usable energy from normal solar panels.

Furthermore if you have a heatpump you can convert this electric energy into heat energy with a factor of >3 (COP).

by karussell

2/3/2026 at 2:38:53 AM

Yeah but if you're in a northern climate your solar panels are only generating like 10% of their summer capacity in the winter anyway due to sun hours/angles... winter is just tough for capturing solar energy in general.

by Marsymars

2/2/2026 at 12:16:40 PM

Where I live we need a way to store and distribute cold as needed.

by animal531

2/2/2026 at 12:54:05 PM

Stanford's cogen plant has an underground "ice cube" for campus/municipal chilled water infrastructure. Perhaps scaling something like that makes sense or perhaps to use an absorption heat pump (AHP) that can operate like and the reverse of an Einstein–Szilard refrigerator?

by burnt-resistor

2/2/2026 at 1:11:47 AM

So it's a large version of those rechargeable hand-warmers?

by chickenimprint

2/2/2026 at 8:49:05 AM

Yes, it's the same tech. There's been products on the market for a while even though this press release tries to spin it like it's new and linked to heat pumps.

by ZeroGravitas

2/2/2026 at 8:42:08 PM

IIRC BMW used to have a form of this in their cars about 25-30 years back so that the hvac would be able to blow heat before the engine coolant was up to temp after sitting overnight.

by mrexroad

2/2/2026 at 12:45:14 PM

Private equity / Wall St. megacorps want to sell you complex systems that are fragile, unaffordable by the 99%, have short warranty periods, wear out quickly, require cloud logins and proprietary maintenance parts, and are mandated by law.

GFL buying a simple resistive-heated clothes dryer, furnace, or tanked/tankless water heater in 2030.

by burnt-resistor

2/2/2026 at 11:04:33 AM

the idea is theoreticaly good, but as it depends on sealing incompatable materials apart, there will be problems, and issues with disposing of failed units.Dry sand works as thermal storage without any issues, and only needs more space, competition will be stiff.Water also works, and ordinary off the floor systems can be used with no modifications. The only advantage the system will have is in places where space constraints combine with the desire for fancy solutions and ecobabble.

by metalman

2/2/2026 at 1:50:31 AM

[flagged]

by RiceNBananas

2/2/2026 at 8:50:14 PM

Stones has the ability to store heat and keep cool.

What's all this fuzz about ?

by danielovichdk

2/2/2026 at 9:31:41 PM

It's all about efficiency. You can store heat in anything, but the question is for how long and how much energy can you get back out later. The first part is easy and how we got ovens and stoves, the second part can be pretty tricky depending on your requirements. Large scale energy storage sometimes uses massive amounts of sand for example, but they heat it to hundreds of degrees which is not really feasible in most settings.

by Etheryte