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Comment by kalleboo | Hacker News Reader

I live in Japan and last year when we moved from an apartment to a house we installed a Mitsubishi EcoCute heat pump water heater which already has these features and is also a CO2 heat pump.

We have one of the "all-denka" electric plans, where we trade off cheap rates during solar hours for expensive rates during duck curve hours. By having the hot water only run during cheap hours, and having the aircon turned off/down during the expensive hours, we're paying less in energy for our all-electric house than we did in combined electric+gas in our 3x smaller apartment.

We pay approx (before fees, and the rates change slightly by season):

* 8 AM - 10 AM: 35 yen/kWh

* 10 AM - 4 PM: 13 yen/kWh

* 4 PM - 6 PM: 35 yen/kWh

* 6 PM - 8 AM: 19 yen/kWh

Our Mitsubishi has other nice features like it can recirculate the water in the bath through a heat exchanger after you already filled it and got in, so it will keep the water from cooling down to lukewarm, and you can even adjust the bath water temperature if you ended up with filling it with too warm or too cold water. Of course, there's also an app so you can start filling up the bathtub when you leave work for home so a hot bath is waiting for you. There's also an intercom to the kitchen "so mom can tell the kids to get out of the bath, dinner is ready".

edit: the wifi integration does have one actually useful feature: if we had solar panels, then it can use data from them to know when to run "for free", and it can use weather data to predict if it should wait for sun or not to run

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In the Netherlands (and the rest of western europe), we have hourly and quarterly energy pricing (opt-in), next to pricing plans that have one or two fixed tariffs during the day/year.

I quite like the quarterly pricing, for example today the home-battery charged for 3 hours during the cheapest time (13:00 - 16:00), and discharged again for the most expensive hours (19:00 to 21:00), and kept my house's grid-input at zero for the rest of the day.

Feeding back a few kwh's during the most expensive hours gives me a big kickback, making electricity use for the rest of the day mostly free. (Since there is usually a 150-250% price difference between cheap and expensive timeslots).

(For price-charts, see https://jeroen.nl/dynamische-energie/stroom/prijzen/vandaag or price-predictions upto a week ahead there's https://wattwanneer.nl )

In Chicago, we have an API where we can get pricing updates every 5 minutes. I recently set up my AC (largest power draw) to cut off when the price goes above a certain threshold.

I don't have long-term data yet, as I just implemented this about 6 weeks ago, but last month's bill was 10% lower than the previous month and the same month the previous year. I'm looking forward to seeing the results over time.

I've been trying to think of what other automations I can try out when the price gets high. I thought maybe shorter light timers for automated lights, but all of our lights are LED, so the savings isn't really worth it.

Do you have a battery so you can time shift and charge it when it's cheap and use the battery when it's expensive?

Many times the battery costs more than the savings, even if you charged it up for free, say at a mall or mcdonalds or something. If there was a large savings the utilities provider would be doing it already. Well that's also why people are looking into cheaper energy storage solutions.

I'm going to disagree with you although I'm not an expert so you might be right.

My understanding is that there are large savings available theoretically at the grid level but the capital to build it is limited and the grid interconnects to make it work are limited.

So globally there are huge amounts of battery storage being added to the grid but this is bottlenecked by capital and grid connections. Oh and land/planning permissions.

Long story short, house level battery storage may be worth it for some people

I guess it depends on how cheaply you can get your batteries and how you charge yourself for the space they take up.

As electric cars become more popular, we should see a deep market for second-hand batteries?

Is this what we call "net metering" here in the US? Unfortunately this region only has "buy-all-sell-all", no intraday prices, and and still not enough storage to store solar from peak at noon until evening commute: https://news.ycombinator.com/item?id=45630917

A market economist might remark that perhaps that shouldn't be surprising given the lack of intraday rates and the buy-all-sell-all policies.

> In the Netherlands (and the rest of western europe), we have hourly and quarterly energy pricing (opt-in), next to pricing plans that have one or two fixed tariffs during the day/year

So your policies create incentives for residential customers to become net producers of electricity (with resilient local storage)?

What battery did you install and how much did it cost?

We have quarter-hour pricing here in Vienna and during the sunnier half of the year electricity is cheaper during the day.

It would be interesting to calculate how long it would take to pay off.

I've bought 14kwh of anker solix max ac for €3900, and added 2 zendure 800 plus's for €320 each (1.9kwh + 2 solar mppt ports each). It's all connected and managed through homeassistant.

I guess if your electricity use is (almost) free, the utility needs to bill you for the use of the grid itself separately?

In the UK we've had off peak power overnight for decades. My current one is something like 1/3rd of the price of daytime power between 2300 and 0700.

However this is somewhat old fashioned, the most modern tarrifs vary on a 30 minute window, with prices set a day ahead. If there's a lot of solar and little demand on say a sunny sunday afternoon or windy february nighttime, then the prices may even go negative.

You want your consumption to be tied into there. You can do this with batteries -- for example on Tuesday I used 34kWh, 24kWh overnight (mainly to charge the car) and 10kWh in the day. If I had a battery I could have charged that battery overnight and saved a couple of quid, or about £600 a year (depends on what my daytime usage is)

However with a 30kWh battery I could have charged it on Sunday afternoon and been paid for that, and not used any power on Monday, Tuesday or Wednesday for the house. But then the agile rate last night was 25p/kWh. I did look at getting a battery and inverter installed but it wasn't cheap.

On top of that you've got self generation. I have very little solar generation, but in theory I reckon I could have 8kWp on the roof -- I'd want to charge the car (and house battery, and any heatpump or ac) when the sun was shining then, which would be even cheaper than charging at night. Home Assistant will do that, but it feels a little fragile with my car charger (if the HA dies, the charger won't start, and then I can't go anywhere. It's not a great charger)

Economy 7 and storage heaters. Heat up bricks overnight using cheap rate electricity so they can keep your home warm during the day while you’re out working.

In fairness it probably works ok for homes insulated to a much higher standard than most British ones.

Why do you need a warm home when you ain't at home?

> Our Mitsubishi has other nice features like it can recirculate the water in the bath through a heat exchanger after you already filled it and got in, so it will keep the water from cooling down to lukewarm, and you can even adjust the bath water temperature if you ended up with filling it with too warm or too cold water.

How long do you sit in a bath?

> Of course, there's also an app so you can start filling up the bathtub when you leave work for home so a hot bath is waiting for you.

My immediate reaction to this is, “there’s a way for my house to be remotely flooded”.

> How long do you sit in a bath?

Another Japan resident here! It is common for a family to share a bath for the evening. (One at a time!) This works because each person showers to get clean before you get in the bath. Many also have folding bath covers, which help to avoid the water from cooling down and to keep the water clean during the showers. Still, nobody wants to be last.

> My immediate reaction to this is, “there’s a way for my house to be remotely flooded”.

A smart reaction! But most baths are also whole-room units, with a floor drain, and are intended to get wet. I myself have forgotten to stop the bath water a number of times (neither I nor my bath are so "smart") and while it is an unfortunate waste of water, there is no danger of flooding, only slight embarrassment.

A Japanese bath sounds a lot more like what Americans call a hot tub.

BTW, Japanese bathing is somewhat visible in My Neighbor Totoro, a really cute movie.

In most ways, yes. E.g. you clean yourself before you get in, so the water remains relatively clean after a few people. Unlike a hot tub though it's drained between uses, so it doesn't really have some of the nastier issues that hot tubs can acquire (nor does it need higher chlorine content to mitigate it).

If you look at a picture of one, they're basically tiny hot tubs.

> A smart reaction! But most baths are also whole-room units, with a floor drain

Nice concept! Do you have any problems with mold build up?

These rooms have ventilation (and also usually a heater, cooling, dry mode). The ventilation can be set to 24/7 mode, which runs at a low setting, always on. Japanese houses/apartments also typically have a house ventilation system, meant to run when it's humid. Mold in general is a problem here, so ventilation is incorporated well.

It's fun in the winter when you're running humidifiers but forget to turn off your house ventilation and don't understand why you're still so dry.

> Japanese houses/apartments also typically have a house ventilation system, meant to run when it's humid.

Do they have Mechanical Ventilation and Heat Recovery (MVHR) or is this more like Aircon? I've recently moved somewhere more humid and I'm looking to get a grip on what other countries do.

From what I can tell it's a just a house fan. The house ventilation doesn't do heating, cooling, etc. It just moves air.

Not a resident but I have friends there and stayed in a bunch of different apartments.

Bath rooms in smaller apartments, and also in hotels, tend to be, literally, whole-room plastic/resin structures, so it dries easier and if mold appears it's in the plastic surface and easy to get rid of it.

I have a friend with a very big fancy apartment, and his huge bath room is covered mostly in tile and has very good ventilation. The bath even has a waterproof TV so you can watch a movie meanwhile!

It's 98% humidity for months, you need to worry about the whole house!

Are you sure about that number?

I live in famously hot and humid Singapore, and it's usually around 70% to 80% humidity here during the day. I find it hard to believe Japan is even muggier?

I just randomly checked the weather for Osaka and Tokyo (on Google) and they have about 60% to 70% at the moment.

No, I exaggerated slightly; but we're past the wettest season now AFAIK.

Unfortunately, it does build up from time to time, yes. However, there is another feature to most bathroom units, which is the room drying feature. It sends warm dry air into the bathroom to dry it. It is also a great tool for the 6 months of the year in which drying clothes outside is impossible. Even so, the appearance of mold can feel inevitable!

> (One at a time!)

That's unexpected.

> How long do you sit in a bath?

80kg of meat can hold a lot of heat. It cools quicker than you think it would. Also, Japanese families often share the bathwater within themselves(but everyone showers outside the tub first), and the water will become lukewarm at some point in that use case.

> My immediate reaction to this is, “there’s a way for my house to be remotely flooded”.

Yep, remotely operating a machinery will always have some risks. Every machinery should have someone with an emergency stop button should be monitoring it at all time, ideally. But it's a well engineered tub auto-fill in the shower room, it effectively belongs to "inherently safe" category of equipment.

Do you have a water drain in your bathroom floor?

This is uncommon in the US, so a bath overflow quickly becomes a significant structural issue.

In Japan it's very common for bathrooms to be wet rooms; likewise South Korea and Taiwan among others.

To add to this, it's so nice. Sit on a stool in the middle of the room and rinse, soap up, scrub to exfoliate, rinse, then roll the lid of the bath open and soak in a sub much deeper than an American one. Bath is programmable to maintain a constant temperature.

Basically a spa experience every day.

I wish more people knew how nice it is! And the toilet is in a completely separate room so there's no contention among one person who wants to take a bath and another who needs to use the toilet.

I just wish dish washers and dryers were more common in Japanese households. I'm in Okinawa where dryers are a lot more "standard", but dish washers are relatively rare.

All my tubs and sinks in the bathrooms have an 'overflow drain' near the top which you are unable to fill beyond. Is there any reason why that wouldn't be sufficient?

It makes the tub taller than it is deep by a little bit and doesn't look as nice are the only reason I can think of. A little bit of splashed water just isn't a big deal in most wet bathroom setups. They could also just put a drain right off the side of the tub.

My Japanese style bathroom here both has an overflow in the tub and a drain in the middle of the room.

Yeah, if the drain in the sink is clogged. US bathroom pipe is 1.25" which will (probably) lead to a 2" and 4" pipe eventually (depending on when, where, and how your house was built ofc). The hole in the sink leads to the same initial pipe.

But USA bath tubs have overflows (redirecting water into the drain if the taps are left on), surely?

In the US, any tub made past about 1900 or so has an overflow drain that prevents overfilling. The adoption of such drains not quite contemporaneous with the adoption of indoor plumbing, but very soon after.

It's the metal plate usually just below the faucet that looks like it might be useless. But it has an opening underneath to let the overflow water in. These are always sized to handle more water than the faucet can output.

This is basically a non-concern in anything but very, very old, unremodeled bathrooms.

The sinks do as well, but it is more obvious.

Im not sure about bathtubs, but in the U.S. it's apparently legal to sell lavatory sinks without an overflow. Ask me how I know.

This puzzled me and I looked it up, and yes, sinks without overflow meet code [1] (but not tubs). So your situation was apparently legal.

But the sibling comment to this one, where a sink had an overflow, but it was not connected, did not meet code [also 1].

Go figure. There must be some reasoning there, but I'm confused as to what it is.

https://forms.iapmo.org/email_marketing/codespotlight/2018/m...

Code sometimes makes allowances for situations which aren't ideal, as long as they aren't deceptive or creating a false sense of security.

So if you have old two-prong outlets in your house from back when, those are allowed.

If you replace them with a three-pronged outlet which is ungrounded, that breaks code.

If the three-pronged outlet is a GFCI outlet labeled with NO ELECTRICAL GROUND, that is allowed.

My last apartment had the overflow drain hole but it wasn't attached to anything. The water just went directly into the wooden cabinet underneath. Madness. Literally worse than not having the hole because it reduced the capacity of the sink. This is what happens when landlords who DGAF hire handymen who DGAF to do all the work on their units.

To be fair to the potential handyman or contractor many overflow drains are integrated into the sink drain before they attach anything. It might have been the landlord buying temu style sinks with fake overflow holes.

Many overflow drains are not or are poorly connected. If you buy a new home, the inspector will usually skip to overflow test because it will likely fail.

Well, it's also legal to sell food that tastes bad. Doesn't mean you should buy it.

Considering that US houses usually either have a crawl space, basement, or are on a slab the lack of a drain is weird when you think about it. You would think wet locations would be required to have a drain.

I think a lot of European houses have floor drains in the bath, you can basically hose the bathroom down.

More on topic. Outside of the US R290 (propane) heat pumps are common. But illegal in the US because the refrigerant manufacturers control the code bodies. You can have a 20lb propane tank hanging off a BBQ which in normal operation is literally on fire. But you can't have an R290 monoblack cause it's too dangerous.

> I think a lot of European houses have floor drains in the bath, you can basically hose the bathroom down.

Weirdly, in the UK it's common to have carpet in the bathrooms.

The tub sits in a big shower booth. Other bathroom amenities like sink and washing machines are installed outside the booth. Toilet is usually a separate room entirely. So no problem overflowing water onto the floor since that's how you take a shower.

Bathroom floor drain is common (might even be a code requirement?) in commercial buildings but not in homes.

I believe it’s mandatory in Australia

Yes, I can't remember seeing a bathroom or laundry here that didn't have a floor drain. Seems insane for that to not be standardised. I briefly lived with a bathroom in the UK that was carpeted?!

i briefly lived in a house that had second floor laundry with no tray or floor drain. the first day after installing a new washing machine it flooded and did over 30k damage to carpet, drywall, and installed electrical. Insurance would not cover installing a floor drain or tray, and the owner chose to let that decision stand.

truly bizarre

> How long do you sit in a bath?

I'm an American and my answer is at least an hour, maybe more, depending on how I'm feeling. I usually listen to an audiobook. Baths are for hanging out and relaxing in.

Reading this comment from an hot european bathtub right now, I've been here for two hours

Don't you get all wrinkly?

I don't mind

https://en.wikipedia.org/wiki/Wrinkle#Water-immersion_wrinkl...

> How long do you sit in a bath?

We love our baths here in Japan

> My immediate reaction to this is, “there’s a way for my house to be remotely flooded”.

I forgot to mention that it senses and automatically stops filling the bath at a select number of liters, even if you start a bath using the physical button when you're at home.

If I'm in the bath I'm either reading a good book, or talking with my wife (I have a tub big enough for two - takes a lot of water to fill) - either way I'm going to be in it for an hour or two. As the other poster said, if I want to get clean I'll take a quick shower. The tub is nice when my muscles get sore and tight from work.

> or talking with my wife (I have a tub big enough for two - takes a lot of water to fill)

Taking your wife into the tub with you is just good economics then. Saves on water necessary to fill the thing p.

While in the US making a bathroom a "wet room" is rare, it can be quite common in other countries.

You can totally remodel bathrooms to be "wet rooms" in the US, it is well worth it.

Kids flooding the bathroom via the tub? Not a problem. Toilet overflowing? Gross, but not a problem.

I wish I would have made all the bathrooms in my home wet rooms.

This was my biggest takeaway from Japan in terms of home design - the bathroom design. At a small apartment in Tokyo the "bathroom" was in fact three separate spaces: a nook where the washer and sink lived which opened into the living room, one side of the nook featured the toilet closet, the other, and actual bathroom with tub and shower. This lets three people use the plumbing fixtures - toilet, shower/bath and sink. Though not all of the places I stayed at split the sink and bathroom.

Contrast this with the all-in-one design where a person taking a shower monopolizes all the plumbing fixtures even while they are not using them. I was on a bachelor party trip with 8 guys and two bathrooms where some inconsiderate people camped out in the shower for 20 minutes while people waking up had to pee so badly they went outside in the bushes. Meanwhile on a trip to Japan with five people we could easily share one or two split bathrooms and never had an issue.

Oh, and the electric bidet is a clear winner in terms of bathroom accessory to buy. Less TP use and no threat of swamp ass that demands you take a shower. Heated seat in winter is a blessing, especially in the morning. After my Japan trip it was the first thing I bought when I got back home.

> How long do you sit in a bath?

The entire point of a bath is to relax and soak in it. Otherwise I'd just take a far more economical shower.

Interesting that that's a feature of the water heater and not the tub. It has to travel through the plumbing all the way round-trip to the heater? You must have isolated recirculation plumbing to deal with the grey water, yeah?

Typically Japanese homes are laid out economically so the bath is right where the hot water heater is. In our house from the 70's it's probably not more than meter through the wall to the water heater. Even in apartment buildings, typically each apartment has it's own tankless gas water heater on the outside wall of the building so it's easy to meter usage separately.

That is what I always see in wet saunas/bathrooms around me. The bathing room is a main feature so things like main plumbing and water heaters are all placed around that to keep it simple. Recirculation additions after that would then be two simple connections off the back of the tub, probably near where the faucet goes.

Technically, you could also just pull refrigerant lines from the heat pump to the bath tub - you probably already run those to the indoor AC units you have in different rooms anyway - or connect the bath tub to the hot water lines you run to the radiators. Both imply a grey water heat exchanger built into the tub.

Depends on setup, of course. If there's a central AC blowing hot/cold air through ducts, you're stuck using a grey water loop. But it is the least attractive setup...

Barring some catastrophic overflow clogging + drain clogging or other issue, your house will be fine! Your wallet may not be.

These are truly _bath_ rooms. The shower and bath are side by side, with the intent that you wash off before hopping into the bath to soak. Thus if the tub overflowed it would just go down the shower drain.

If you have a delayed start dishwasher or washing machine, you already have that.

Most baths (in the UK at least) have overflows right so the primary risk is just wasting a lot of water?

Every bathtub I've met has an overflow drain near the top, although maybe that drain is smaller then the output of my faucet, good thing mine isn't connected to the internet :D, YMMV.

Not OP but I used to sit in a bath for a long time reading, gradually adding the hottest water to keep it at a nice temp. It's been a while tho, but I'm sure there's someone like me out there :)

As an American reading this I feel like we have fallen far behind when it comes to home HVAC (and bath) tech.

Japan has no domestic source of oil or natural gas. The US has so much natural gas that it’s flared off to the atmosphere in some places. Natural gas is insanely cheap to heat with as a result and condensing boilers are extremely efficient. This created a scenario where heat pumps may be more efficient, but they might still cost more to operate. The raw cost of gas excluding pipeline and connection costs in my state is $0.57 for what is equivalent to 29.3kW of electricity. It’s very hard to beat that if you have a 98% efficient boiler, even with a COP of 4 if you’re paying $0.15/kWh, that means the equivalent amount of heat moved would cost 0.15*7=$1.05 or just under twice as expensive.

Yep - where I am, it's moderately more expensive to use our heat pump to heat the house (at basically any time of year) than to use the gas furnace, and approximately nobody has a heat pump water heater. And with datacenters trying to move in, that equation may get even worse in the future. Gas is surprisingly, weirdly cheap, often not even metered in apartments.

Having two options during cold winters can pay for itself with one emergency repair though, or be a massive savings if it can't be fixed fast enough and pipes burst.

The backup heat source of a heat pump is extremely nice to have if your furnace craps out, just shut off the gas supply and let the heat pump do its job. If I had to replace my A/C condenser I’d probably opt for a heat pump to replace it so that I’d have that option too.

    > Gas is surprisingly, weirdly cheap, often not even metered in apartments.

Yikes. How is this possible? My guess: You are paying for it in a building fee.

Generally yes. But also it is sometimes like half the cost or less for comparative heating power, and for air-heating an apartment in the middle simply doesn't need anywhere near as much, and you literally heat each other so actually-fair costs are fuzzier. Gas bills in places that didn't include it would often be like $15/month in the middle of winter, hardly worth the administrative and hardware costs.

One of the houses I rented many years ago didn't even have metered gas. We paid a "hookup" fee to the city (like... $40/quarter?), and they didn't care how much we used, as long as it wasn't for commercial purposes. I assume the city had something for detecting extreme use or leaks, but that's probably it. It was a somewhat strange property though.

> and you literally heat each other so actually-fair costs are fuzzier

What you're describing is closest to "actually fair" I think we can get. A neighbour of someone I know leaves their apartment empty for long periods of time and when they're gone they just shut off their heating completely and leave all of their neighbours to pick up the bill - each apartment has their own heating system but they share walls, floors, and ceilings.

> The raw cost of gas excluding pipeline and connection costs

In Ontario Canada; your gas hookup is CAD$29/month (~US$21) every month of the year, on top of a per m3 charge for delivery to you before the gas cost itself. So on a smaller or well insulated residence, capping that pipe really helps push the economics in favour of heat pumps.

https://www.enbridgegas.com/-/media/Extranet-Pages/ontario/r...

> It’s very hard to beat that if you have a 98% efficient boiler

You do not, to be clear, have a 98% efficient gas boiler. You _may_ have a gas condenser boiler which claims 98% efficiency in absolutely ideal circumstances, but realistically you're likely not getting close to that. AIUI 80% efficiency is fairly normal for real-world condenser boiler usage (non-condensers were more like 70%)

Anyone who has used a nice Japanese toilet knows the US is behind in terms of bathroom tech, but personally I'm glad that nothing my bathroom is controlled by app and that I don't have to spend my time worrying about what time of day it is when I want hot water or air conditioning. I hope my power company never decides to start with "surge pricing" so they can hike up my rates any time it's too hot or cold outside.

Solar + batteries is cheaper than ever. Americans are often full preppers and DIY but when we speak about energy autonomy and efficiency they immediately get some weird allergy.

Electricity here in Quebec is dirt cheap, state owned and 100% renewable. Our first 40 kWh per day is 7 cents per kWh which is roughly 0.05 USD.

Any calculations I've done made it unfortunately useless to buy solar and instead favoured investing the money in the stock market.

Absolutely in that case it would be more for fiddling and having a conversation starter with friends. It also depends on how reliable your grid is etc.

Some of us still believe in market incentives.

People keep saying this and yet I struggle to find a decent sized house battery that doesn't cost as much as a new car.

What kind of electricity usage do you have? Because a used electric car probably around 20k provides you with easily 50+kwh in car to grid, + you get a working car for free.

Don't feel bad. I also live in Japan, and in my experience most homes (mine included) still use gas boilers and kerosene heaters. Not to mention that houses are built to be as cheap as possible, so insulation is almost non-existent and you boil in summer and freeze in winter.

Yeah, mini split ACs are so superior to American-style central air. I installed them into a couple rooms and removed the central air ductwork from the attic there. Thinking about doing it with the other rooms. Less power usage, every room gets its own temperature setting, quieter.

I've also got the ecocute but I was told that it's cheaper to just pump fresh hot water into the bath than recirculate the cooled down water. It uses less energy to pump the already boiled water into the tub than to heat it back up.

I don't see how that is possible. Either way you need the same amount of heat added to the tub. Maybe you save a little because the return pipes are not cooling the water, but otherwise the needed heat should be the same. I personally insulated all my hot water pipes which solves that worry.

Though fresh water and letting out the old will clean the water you are soaking in, which may be valuable.

The way ecocute works is that it heats water at times when electricity is cheap and stores it in a highly insulated tank. So if you’re having a soak in the evening, it’s cheaper to use the water that is already preheated at cheaper rates and stored, than to reheat it again using the expensive to peak time rates.

My rates are 36yen from 6am to 10pm and 19yen on the other end.

Re-reading my earlier post, I should’ve said cost and not energy.

I suspect what you were told is a misunderstanding.

> recirculate the water in the bath through a heat exchanger after you already filled it and got in

Huh. Is the heat exchanger located near the bathtub or in the EcoCute unit? And do you need to do anything complex to periodically sterilize the tub side of the pipes and the heat exchanger?

Omg the bath features, my dream!

> Our Mitsubishi has other nice features like it can recirculate the water in the bath through a heat exchanger after you already filled it and got in

Interesting! Is there some sort of filter system you can easily clean out, to avoid any issues?

It’s like human sous vide

How does cleaning of the heat exchanger work? From my experience with Jaccuzzi-style baths anything that recirculates bathwater gets very nasty very quick and is a nightmare to clean.

in Japan you tend to shower & wash yourself clean _before_ getting into any bath. In the west people don't do it or do it very half asset. And tbh. a lot of places have combined bath/shower so you kinda can't even do it Japanese style nicely.

That alone probably will make a huge difference in how often you have to deep clean it.

> you kinda can't even do it Japanese style nicely.

I mean you can as long as you make the bathroom a wet room and shower outside the tub, which is exactly how the Japanese do it.

my point is most _rented apartments_ are not setup like that and do not provide a reasonable path to have it

most owned apartments also are not build in a way where it's easy to retrofit. So if you don't do a "in depth" renovation anyway, its often just not a good option from a financial POV. Especially if you have to reroute plumbing (for the floor level wet room sink), especially if beton floor or pre-existing floor heating is involved.

Yes. But then those wouldn't be the places which GP was talking about, where the shower head is set up so you stand in the bath tub to take a shower.

I’ve used a bunch where the shower head is on a hose not fixed to the wall. Usually with a two-way faucet.

The biggest issue in the west is the room being wet to start with.

Holy crap that re-circulation feature is luxurious!

I'd love to have something like that!

Whenever I take a hot shower I fantasize about putting in a liquid-to-liquid heat exchanger so the hot water can heat up the cold water and you can run the hot water at a much lower temperature.

This application with the bath tub feels way more justified.

That does exist. Simple versions just have a large, deep drain with coils the cold water runs through. Fancier ones have a proper heat exchanger next to the shower (requires a pump) or in the basement. Water sanitation rules probably make it non trivial to get a design certified.

Is the deep drain to diminish the air pockets at the exchange surfaces?

It's just so the cold water pipes sit in a pool of warm water. https://www.meanderhr.com/wp-content/uploads/2012/11/HXdrain...

This is even simpler: https://warmduscher.de/produkt/warmduscher-original/

Here you go: https://www.homedepot.com/p/Hydro-Systems-Fusion-Low-Voltage...

Drain heat exchangers are really expensive, this 3” by 48” copper one costs over $1000: https://www.homedepot.com/p/Power-Pipe-3-in-x-48-in-Drain-Wa...

Many people have thought about the drain heat exchanger. However drains need to be way oversized for various reasons and so you can't get good contact with the water: it is mostly air in the drain pipes.

And this is the builder-grade model we got from the house renovation company. There are higher grade ones with fancier stuff...

Presumably you need a bath with extra plumbing? What happens when the heat exchanger gets clogged with soap and hair?

you dont have a passive solar water heater?

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