How to Take a Shower in Germany




OK, for some reason you are staying in Germany, but you did not have the financial means to check into a ****** hotel. Now even if Germany can be mistaken for being a civilized country, a large number of their houses are less comfortable to live in than a Mercedes or a BMW. Since these cars do not come with  bathrooms as part of their standard equipment, you must resort to the facilities found in the house where you are staying. If you are out of luck, your bathroom is eqipped with a thing like the one shown in the picture above, the dreaded "Durchlauferhitzer".

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Step 1: Leaps and Screams

You strip naked, grab your shower soap, and jump into the shower cabin. Then you turn on the water and curse. It's friggin cold. Well, maybe it takes some time for the heater to get going, or for the water to reach your shower from the central heating.

No. The water remains as cold as a cod fart. Since you're child of your time, you guess that the machine on the wall must be programmed in some way. Before you reach it, you have time to get worried about your smartphone: Was it quad-band or only tri-band? Will it be able to interact with the heater?

Wrong. As you can see in the picture above, there is ample reason to despair. The dumb thing does not even have a power on button. (No, not even on the sides that are facing away from the camera.) Well, "one dot" and "two dots" are at least labels that are gender neutral and perfectly incomprehensible regardless of cultural background.

You give up and call one of the natives. After some battle tank gearbox noises in your ear, you have learned that the thing is fully automatic. You just have to open the tap some more, then the heater is turned on. The native explains that a "Durchlauferhitzer" heats the water on the fly (swim?), as it passes through the thing. There is no reservoir with hot water.

With new hope you step into the shower and open the tap, some more, then some. When the flow rate rivals that of the river Rhine, the box on the wall finally goes "clack". Within seconds, the water goes from "cardiac arrest" to "cerebral haemorrhage", and you slam the tap shut in self defence.

After experimenting for twenty minutes, your performance remains erratic. The machine goes "clack" or "thunk", that is, turns the heat on and off, respectively, virtually at random. Most of the time, the water actually gets colder as you open the hot water tap more, but sometimes it can suddenly become much, much hotter. What's the deal? Who invented this piece of <censored by the instructable team>? Is he still alive? If yes, where does he live?

Stay cool. I'll explain everything in the following steps. Above all, don't scream and throw the thing out the window, your neighbours will call the police. (...not because you vandalised the bathroom of your flat, or because you threw the "Durchlauferhitzer" on the street, the Germans do that all the time. No, they'd call the police because you screamed.)

Step 2: One Dot Theory (and Practise)

I will now explaine the principles of the "Durchlauferhitzer". Please turn the operating nob on your "Durchlauferhitzer" to ".", shut the coldwater tap completely, and concentrate.

In the heater, the water flows through a flow rate relay. It consists of a constriction combined with a differential pressure switch bridging it. When the flow through the constriction is large enough, the pressure drop over it will be sufficient for the switch to close. The relay is, you guessed it, connected to the heater.

The heater is a simple resistive electrical heater, with constant power, typically a handful of kilowatts. Now, since the power is constant, but the flow through the heater varies, the resulting temperature depends on the flow rate. To be precise, the temperature will be inversely proportional to the flow rate, once the relay has activated the heating element (see diagram above).

This explains some of the frustration in the shower. As you turn the hot-water on, first nothing happens. Then, "clack", suddenly it's too damn hot. Well, judging from the diagram, the solution is to open the hot water tap some more. Counterintuitive, sure, but that is how it works in reality too.

One interesting consequence is that as long as the flow rate through the hot water pipe is large enough to keep the heater on, it does not matter if the water at the shower head is a mixture of a small amount of water that came through the "Durchlauferhitzer" and a small amount of cold water, or a larger amount of water that was heated, as long as the total flow rate at the shower head is the same. That is, the cold water tap and the hot water tap has the same influence on the temperature!

So, a good strategy is to open the hot water tap generously straight away in order get past the peak quickly. The diagram really shows the situation at steady state. The peak will not be as hot if you rush past it.

Step 3: Two Dot Theory

It is almost true that  the second dot mode is to be used when two persons are taking a shower together. This mode enables a second heater coil in the "Durchlauferhitzer". It is something like a second zone in an afterburner, too hot to handle for most of us.

The second heater is activated at a higher flow rate than the first. The resulting characteristic is shown in the diagram above. If you are an shower greenhord, and are unfortunate to step into a shower cabin powered by a "Durchlauferhitzer" that is in its two dot mode, you will have some serious fun. Not only is the flow rate - temperature characteristic discontinuous, and the slope mostly negative,  you will be thrown off by the time lag between your commands and the temperature change at the shower handle.

If you are lucky, you can hear the "clacks" and "thunks" of the heater. The worst case is when the heater is in another room. You cannot hear a thing and will have to learn to shower like Yoda.

The bottom line is, if you can get enough hot water in the one dot mode, forget about the two dot mode.

Step 4: Extra Credit

In this section (or step, if you like), I will describe some more advanced consequences of this hideous invention.

Thermal Mass 1
In Germany, pipes and cables are often buried in the plaster of the wall, with no isolation around them. This gives the pipes a substantial thermal mass. If you start your shower by making your hair wet, followed by a short pause where you shampoo your hair, you are in for a big surprise. Even if you had the water turned off for only a few seconds, the first spurt of water you get after the pause will be as cold as the wall in which the pipe is laid. A considerable amount of water must flow through the pipe, and the wall, before this effect fades.

Thermal Mass 2
In the heater, where the water is heated, the water flows through a curvy channel of copper. The thermal mass of this part of the heater can manifest itself through a painful surprise. The heater coil side of the copper channel is quite a bit hotter than the water side at steady state usage. If you start out at a flow rate close to the "thunk" threshold, where the water is at its hottest, and then abruptly shut the water off, additional heat will flow from the electrical heater coils to the water in the copper channel. If you turn the water on again within the next few seconds, you will be awarded with a spurt of increadibly hot water. To be perfectly honest, it is not water anymore. The substance which is produced in this way, is more adequately described as plasma. After you are done with your shower, you can toast bread on your naked skin.

The More the Merrier
This is a no-brainer. If the "Durchlauferhitzer" is connected to more taps than those of the shower, you are in for some serious fun. Your efforts to outsmart the heater will be utterly futile, as soon as a second person becomes part of the equation. He/She can increase the flow through the heater above the second threshold, or, just as bad, steal some of the hot water. Consumtion of cold water can also upset the carefully adjusted equilibrium of your shower. A liberate consumtion of cold water can lower the pressure available to your heater. Unless you adjust the taps, the flow rate may drop below the threshold. The header goes "thunk" and you will scream and jump anew.

Nonlinear Effects
If the hot water and cold water are lead through a common exit, you can turn off the heater by increasing the cold water flow. The reason is that the outflow is becoming blocked by the cold water flow, thereby reducing the hot water flow. If it was close to the threshold, the heater may shut down.

The most interesting nonlinear effect I have ever noticed, is one that was caused by the thermal expansion of the tap. When heated, the spindle in the tap expanded and restricted the hot water flow. If carefully adjusted, this change was enough to turn the heater off. The water cools and the tap spindle too. The flow increases and the heater is turned on. We are back were we started.

Step 5: The Future of the "Durchlauferhitzer"

It should be clear from my instructable that the "Durchlauferhitzer" is a very primitive and barbaric device. Surely, there are better solutions today. You are perfectly correct. The top of the line "Durchlauferhitzer" of present day Germany have gone electronic. They are equipped with temperature sensors that measure the temperature of the inflow as well as the outlet water, and they measure the flow rate. These measurements are monitored by an electronic brain that adjusts the heater power so that the outflow keeps constant temperature within a fraction of a degree.

The modern day heater has several buttons, an LCD display, and the user can select one of several operational modi. The top models even have a wellness mode. In this mode, the temperature changes periodically between too hot and too cold. Yep. Here in Germany, people think this will improve their immune system.

Health through pain. A popular concept that refuses to die.

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    130 Discussions


    3 years ago

    Why are there "****" blocking non curse words on websites? I can never figure out what the writer was trying to say. It stops my reading flow and angers me. Its not just on this site. Sometimes when i reading on another site the subject im reading about say "mufflers" gets stared out. so further into the conversation it goes my ********* is hot and ********* suck anyways. that could be anything.


    3 years ago

    ... and since i didn't understand almost all of this, I wont ever be visiting Germany. Or i will bring wet wipes and stay less than 3 days.


    3 years ago

    Well this "durchlauferhitzer" is what we call "tankless water heater" and it's briliant device if your water consumption is not too high. You can read more about it here:


    …I'd call that a top floor problem.

    very few of the numerous german durchlauferhitzer I've had the pleasure to encounter showed such brutal behaviour. but especially on top floors of buildings where the system pressure might be lower and the durchlauferhitzer is "last consumer in line", changing flow rates are a problem for the dinosaur ones.



    6 years ago

    Brilliant. I have been this soldier! Scalded and frozen and half wet and resorted to boiling a kettle to bring the tub to tepid.


    6 years ago on Introduction

    I would seriously love to know where you stayed that you had to use one of these. The last time I've had to bother with one of these was at my grandparents' cabin where the bathroom is in a seperate building because the thing is just that old.

    I'm 22 and have lived in Germany most of my life. Believe it or not, in all places that I've lived the showers were much more modern and comfortable than what you describe. Thus I don't apreciate you calling one of the most efficient industrialized nations that I've seen to date one that "can be mistaken for being a civilized country."

    So while, yes, these types of heaters do still exist they are a tiny fraction and most people in my generation probably would be just as baffled by them as you must have been the first time you saw this. Just felt the need to make that clear.

    9 replies

    Reply 6 years ago on Introduction

    There are some WWII vets that might tell you, it happened immediately at the close of the Second World War. ;)

    Besides, they are home to BMW, the most refined and civilized automobile affordable to man.


    I live in germany and have done for more than a decade.

    first of all these things are all over the place.

    secondly if these have not been fitted properly ,the flow rate/pressure isn't strong enough or fluctuates, the wrong unit( for the size of pipes fitted ) is used then it will not work properly.

    You can still buy these and plumbers still fit them badly even when you employ a "meister"

    and I understand you wanting to defend your nation but this-

    buddhafragt says:
    if you are too stupit to handle a Durchlauferhitzer, you better ask a local people.
    But it is soooo easy: Only turn on the water....
    Cant be soo difficult, even for an American.... ;-)

    is nothing more than ignorant , offensive, pathetic and a sad indictment of the world we live in.

    at least this instructable was humorous.

    I've just finished reading all the comments below and thought the following points worth noting.

    I have recently fitted one of these to replace a boiler that took 8 hours to heat! so it is easily more cost effective to run.

    mine has electronic temperature control. I paid 50% more than a standard instantaneous heater because I have used these before and know what a pain they can be.

    european domestic supply is between 220v and 240v dependant on where you live.

    In germany it is 220v but these appliances have what I believe is called a 3 phase power connection and have 3 live power inputs.

    So if you get a shock from one of these you are likely to get 660v through your wet body which ,if the warning on the box is correct ,suggests will probably/maybe kill you! or at least hurt a lot!

    Billy 3 phase power does not mean 3 times the voltage. The voltage peak on each wire leads or lags the other wires by 120 degrees.

    okay I'll take your word for that, I'm a chippie not a spark.

    The point I was intending to make was, that these units take a far higher degree of technical competence and should not be confused with a normal u.k. domestic electric shower which normally use a normal domestic supply and are really an easy d.i.y. upgrade.

    My point still stands though it would hurt lots.


    Reply 6 years ago on Introduction

    Then I'm even more curious where he lives. Because I in all seriousness cannot imagine where in the country this could be anything but an oddity.


    Reply 6 years ago on Introduction

    I agree ... I have spent 29 years of my life in Germany and the only person I can remember having one of those is my granny and she still has it.

    Any other place in Germany I have ever been showering at did have the same standard as any hotel. Actually I have seen less comfortable solutions in other countries.

    Have a good day !


    6 years ago on Introduction

    Hi all of you!

    I am blown out of my socks by all this feedback. I hope you understand that I cannot respond to every comment individually. If I tried, I'd be sitting here until well after X-mas.

    It is amusing to see how quick some of you have jumped to conclusions and accused me of all kinds of things. Well, I suppose it can be held against me that I cannot resist the temptation of adding to my own amusement, and that of all my supporters, by revealing the following facts about me:

    I am not from Germany, I am not from USA. I have lived one year in USA and eight in Germany. Cheers

    p.s. Don't miss my new instructable about how to peel a banana like Jonas.

    1 reply

    Reply 6 years ago on Introduction

    You're only nine years old??!! I can see it in your (I assume) self portrait, but man, now I'm even more impressed by the instructable. Seriously though, I enjoyed reading it, it was instructive, well-researched and funny -- I especially liked the end, when you describe the digital heaters designed to oscillate between hot and cold. Don't let the nay-sayers get you down, they are part of the loud minority. I used to think that if someone misunderstood my writing the fault was always mine, but now I know, especially with humor, that it not the case. Someone is bound to miss the point and take offense. I once had someone complain that my vegan egg instructable was a cheap, deceitful trick to get views -- he was mad because it wasn't an actual egg.


    6 years ago on Step 5

    I think I will stay in Canada. One knob to control the amount of cold water going through the pipes and another knob to control the amount of hot water.


    6 years ago on Step 5

    Better instructable I ever read! I never thought I'd laugh as I read reading an article on this site. Congrats!!!


    6 years ago on Introduction

    we have a gas battery sparked water heater that works just like that. its for camping