103

I do not understand the advantage of the popular "hot" and "cold" controls in showers, as opposed to "temperature" and "quantity" controls.

Is it simply because the latter option is harder to implement? Why isn't it more common? It would make much more sense for the user to be able to control the temperature and the quantity as discrete items rather than how it is now.

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    To match the taps on sinks, I guess. Also, many showers do have temp/strength controls. – Steve Jones Apr 4 '15 at 11:47
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    Most showers here in the UK (in my experience) do have one control for temperature and one control for pressure (examples). Mostly you only see 'hot' and 'cold' where it's the kind of half-assed shower that's just a cheap add-on to bath taps. – A E Apr 4 '15 at 17:04
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    @SteveJones then why do sinks have hot/cold controls? Same issue. – usr Apr 4 '15 at 18:07
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    I agree the premise of the question is flawed. You are assuming prevalence one particular design but I see no evidence of that. – Lightness Races in Orbit Apr 4 '15 at 23:13
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    @usr: many sinks do have temp/strength controls on mixer taps ;-p That said, on taps typically it's not a thermostatic temperature control, the hot-cold axis actually controls the proportion of each water supply. My shower has a mechanical thermostatic temperature control, though. – Steve Jessop Apr 5 '15 at 4:19

13 Answers 13

109

You are totally right

As with many other devices (eg the QWERTY keyboard) the hot/cold tap persists not because it's the most usable design, but because of:

  • Cost since proper temperature control requires an electromechanical feedback loop design, or calibrated thermostatic valves which needs to be periodically adjusted or replaced. This drives up the cost of the faucet significantly.
  • Convention (aka the legacy problem).

That said, there are temperature/pressure controls available today, and they are AWESOME to use. You can do a search for thermostatic shower faucets (or mixers, or valves) to find out more.

Pressure-temperature faucets are used with varying frequency around the world (see comments below), and I've seen them in Japan and various countries in Europe and Asia.

These faucets are particularly amazing for filling baths consistently because water has a pretty high specific heat capacity so getting the temperature wrong by just a few degrees while filling a bath means spending quite a of time waiting to get the right temperature or adjusting the water mix.

Here are two common designs....


1. Mixer-style thermostatic shower faucet

  • Here is a popular format with end-mounted temperature and flow knobs common in Japan and elsewhere:

    enter image description here

  • These faucets often have a lock, label and/or a click affordance around 38°C to provide additional ergonomics around safe water temperatures.

  • For more background on how these work, this brochure from Delta Faucets is quite informative.

2. Instant electric water heater

  • I have not seen these in Europe (that's not to say they aren't available or used), but have seen them in many places in Asia. Here is a typical format with temperature and pressure knobs:

    enter image description here

  • These systems use varying combinations of electric/mechanical/electromechanical innards to provide separate pressure and temperature controls from a single cold-water input.


One more thing...

There are other pressure-temperature formats available including some crazy high end designs like this one with 4+ shower heads, steam option, custom lighting, ambient music, remote control, storable user presets, and more:

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    The type of shower control pictured is also normal here in the UK. – A E Apr 4 '15 at 17:02
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    I'm not from the US, and the one in the picture (or similar ones) are the only knobs I've ever seen – Thomas Bonini Apr 4 '15 at 18:32
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    japan? That's really funny – my parents have 'exactly' the same, made by german company GROHE – tillinberlin Apr 4 '15 at 20:03
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    That's also very common in Germany, too. Got mine in the shower last month. – Uwe Keim Apr 4 '15 at 20:24
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    "since proper temperature control requires an electromechanical feedback loop design" there is no need for this kind of precision control in a shower. A simple mixer that goes "a bit hotter" or "a bit colder" is more than sufficient. – Matt Burland Apr 7 '15 at 17:27
33

I suppose it's mostly a question of how much money you want to invest into your fittings. In most cases you'll have one pipe for hot and one for cold water. The knobs then just open and close those pipes – I can hardly think of any easier / cheaper solution. However there are actually different solutions that do exactly what you describe:

  • Visiting Canada in the late 80ies I was confronted with shower controls for 'temperature' and 'pressure'. I don't know if that was a tailored system, but it was confusing anyways. One difficulty was also, that depending on the pressure, the temperature would slightly change – so you always had to adjust both knobs.

  • At least in Germany you can buy 'mixing batteries' for about twice the price regular fittings would cost. Moving the hand gear up and down controls the pressure – moving it right-left controls the temperature. Leaving the handle in the centered position you'll always have a comfortable 'warm' mix.

From a UX point of view I would recommend the latter – it also minimizes the problem of getting dirty hands clean while not getting clean fittings dirty.

enter image description here

ps: for everybody who "have never seen a shower that has separate hot/cold knobs like you describe" I just have to add this photo of a 'regular' (cheap) shower fitting in Germany/Berlin with two basic knobs hot/cold:

enter image description here

  • Those two-knob taps used to be very common in England. I think my grandmother still owns one. – Pharap Apr 7 '15 at 20:36
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    "Mixing battery" means it has just one outlet for both hot and cold water, so the thing in the second picture also qualifies as "mixing battery". It's been the default in continental Europe for ages. The only place I've seen two separate taps is England (and it's disappearing there as well). – Jan Hudec Apr 8 '15 at 6:30
  • Huge advantage of the lever mechanism is that it's basically maintenance-free as it's ceramic seals don't wear off and always seal tight while the taps with knobs (valves) start to tap over time and need replacing of the seals. And the levers are easier to operate. – Jan Hudec Apr 8 '15 at 6:33
  • Ah yes! The bottom picture brings back memories. I still yearn for the days when finding the right temperature was simple... I often find that the new ones are actually harder to operate. Especially the ones with the lever (first picture) tend to be very finicky... Move the lever a bit too far and it's burning hot... move it back and it's cold again... Can be that i'm just a bit too spastic... :) – Stijn de Witt Jul 22 '15 at 22:39
19

I can honestly say I have never seen a shower that has separate hot/cold knobs like you describe, and I've lived everywhere up and down both the east and west US coast.

Every shower I've ever seen has two concentric wheels. The inner one controls temperature while the outer one controls pressure.

Here's what they look like (although the labels around the outside seem all wrong... unless they mean to say the shower is only comfortable when off...):

enter image description here

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    I don't think your experience of showers is representative - there are lots of other common designs besides this one. – Nate Eldredge Apr 4 '15 at 17:35
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    "'Ive lived everywhere up and down both the east and west US coast" You must not have lived anywhere particularly old. Because I live on the East US Coast and I know besides newly renovated houses, most of the people in my area have the separate hot/cold knobs. – JPMC Apr 5 '15 at 0:16
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    @jamesqf Although the hot tap is usually on the left, every dial I can think of (clocks, car speedometers, volume controls, taps/faucets, ...) turns clockwise to increase whatever it's controlling or displaying. It would be extremely confusing if this kind of shower went the other way: "things increase clockwise" is much more intuitive than "hot tap on the left". – David Richerby Apr 6 '15 at 19:36
  • Comments are not for extended discussion; this conversation has been moved to chat. – Benny Skogberg Apr 8 '15 at 3:42
  • Hot tap is (was) almost always on the left. The reason for that is simple: People tend to use cold water more often than hot (remember, same design is used in the kitchen). People tend to be right handed. Putting the hot tap on the right would mean you would have to operate the valve on the 'wrong' side most of the time. I have seen examples were it was reversed. I still remember these because the caused me to burn my hand/mouth when expecting cold water and getting steaming hot water instead. ... The labels around the side seem right in that its nearly impossible to find the right temp... :) – Stijn de Witt Jul 22 '15 at 22:45
12

Hot and cold knobs work great, and everyone intuitively understands that turning the knob makes more water come out, ie more water pressure. The practical reason is it gives maximum control with the fewest parts. Also, the range for usable water pressure is not very large, and dedicating an entire knob to it seems to be a waste. Your solution would require more complex combination hot/cold valves for the temperature control, yet offers no practical benefits.

From a UI standpoint, what happens in your system when I turn the temperature knob, but water strength is at zero? Nothing comes out? That is confusing to someone who knows turning either knob make water come out. I fail to see how that is better, when the original system gives feedback regardless of which control is used.

As far as controlling the temperature and pressure separately, that's exactly what hot/cold knobs already do. Too hot, add a bit of cold. Not enough pressure, turn up both knobs the same amount.

That sell shower controls similar to your description and I wouldn't call them better. I have them at my house, and I cannot stand them and wish I had hot/cold valves.

Separate Hot/Cold valves is a simple analog solution that just 'works'.

edit I may have oversimplified some aspects, but the basic thing it boils down to is COST. The fancy temperature controlled shower head show above is much costlier than simple hot/cold valves. I think some folks get spoiled designing UIs where fancy controls are 'free'. We are dealing with actual, physical items that break here, not UI controls. Home builders look for the most cost effective solution that works and is easily repaired. That is traditional hot/cold valves

  • 5 answers and no up/down votes. +1. Separate hot and cold controllers are also helpful to provide hot water for multiple rooms. In some countries, there are solar powered water heaters, and a "hot" line goes throughout the building. It's always in the same higher temperature. Mixing up regular line (which is cool) at the very end of the shower can save the temperature of the hot line. – Ayesh K Apr 4 '15 at 16:47
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    Another problem is that (unless you have point-of-use heaters mounted really close), there is going to be some seconds of lag between adjusting the temperature control, and having the water actually at the specified temperature. – jamesqf Apr 4 '15 at 18:11
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    Your claim that it's confusing to have a control that does nothing if the water isn't flowing is silly. You're presupposing that it's right to "know" that all controls must do something at all times but I would suggest that it's obvious to most people that the controls of any device will give no feedback if the device is switched off (which a shower is, when the water isn't flowing). For example, people have no difficulty with the idea that retuning a radio that is switched off has no effect until the radio is switched on. – David Richerby Apr 6 '15 at 9:43
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    @DavidRicherby or I can put the pedal to the metal on my car in my driveway when my keys are in my pocket. The user training to get accustomed to a new faucet design seems pretty minimal. – Brad Apr 6 '15 at 21:27
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    You say “Not enough pressure, turn up both knobs the same amount.”  You oversimplify.  If I have to turn one knob 90° and the other knob 150° to get the temperature I want, but then I need to increase the water flow 33⅓%, I need to turn the knobs 30° and 50°. – Scott Apr 7 '15 at 4:50
10

They don't any more. They used to because it is the most mechanically simple implementation of temperature control. However, this is only historical.

None of the other answers mention the legalities of this. The International Building Code (what most US local codes are modeled on these days) mandates that all new shower controls must be temperature regulating design.

International Residential Code Chapter 27, P2708.3 Shower control valves:

Individual shower and tub/shower combination valves shall be equipped with control valves of the pressure-balance, thermostatic-mixing or combination pressure-balance/thermostatic-mixing valve types with a high limit stop in accordance with ASSE 1016 or ASME A112.18.1/CSA B125.1. The high limit stop shall be set to limit the water temperature to not greater than 120°F (49°C). In-line thermostatic valves shall not be used for compliance with this section.

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    Most local government ordinances adopt new regulations slowly. So while this one entity may recommend these codes be adopted, the reality is that much of the US is still using building codes that are a decade or more old. Saying, 'They don't any more." is simply incorrect. – Adam Davis Apr 7 '15 at 14:03
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    > "They don't any more." — seems like you didn't visit Russia. ;) – Sarge Borsch Apr 7 '15 at 14:39
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    Oh my god, someone with a serious and backed-up answer. Finally. You should mention that, while modern codes may require new buildings to have temperature/pressure controls, lots of older buildings still have hot/cold controls. – KRyan Apr 7 '15 at 19:00
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    The reason for this code is fairly simple: burn injuries are unfortunately all too common among elderly, who have problems feeling that the water is too hot and/or getting out of the shower when it is too hot. – MSalters Apr 8 '15 at 11:31
  • @MSalters That's probably the single most important benefit of the pressure/temp regulators versus hot/cold. With the old hot/cold controls it was all too easy to set the temperature to blisteringly hot. Not so with pressure/temp controls. Good point! – Stijn de Witt Jul 22 '15 at 22:52
3

I found it very amusing reading all these answers which I assume were written by people in the US.

I live in the UK and visit France and Spain very regularly. I believe a resident of any of these countries would be appalled to find a hot/cold shower in a hotel room in Europe - I have not seen such a thing for many years.

All the talk about the the difficulty in manufacturing temperature/flow showers should bear in mind that there may well be 1 billion of them in Europe, and I don't think we can generalise that Europeans are generally wealthier than Americans.

To put in context, I recently had a new shower installed and the shower valve is a ceramic disc, thermostatically controlled mixer with 4 independent flow outlets. The valve cost around £600.link. This very much the "Rolls Royce" of shower mixers, but http://www.screwfix.com/p/swirl-vino-thermostatic-mixer-shower-flexible-exposed-chrome-effect/39565 this is a much more basic model for £45 with all the external kit included. I've seen the valve alone for £40 before. Many people are now installing the next evolution where the temperature and flow are controlled digitally and are adjusted using buttons. Each family member can program their own preference so a single button press will set up the shower to their requirements. I know someone who has had one of these for about ten years.

The point being that these are standard kit in Europe (and Japan by the sound of it) so I think it's safer to ask the question "Why do Americans persist in using hot/cold showers?"

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    At today's exchange rate, £600 = $895.20. (But your link lists it at £739 = $1102.59.) May I politely suggest that some people might just have too much money? Or at least, used to have too much before they paid the plumber for the fancy shower :-) By contrast, I can go my local Home Depot and choose from a number of 2-knob versions under $50: homedepot.com/b/… IMHO they're much easier to use, too. – jamesqf Apr 5 '15 at 17:34
  • @jamesqf I've clarified a little to emphasise that my £600 is not the norm. The price mentioned on the link is the price that no one pays - discount is standard and my plumber got mine for around £550 but I couldn't remember the exact price. – Lefty Apr 5 '15 at 20:17
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    @Lefty: That's just the point. Those complicated, expensive shower controls are neither easier nor inherently safer, they're just a way to get people to spend more money on unnecessary glitz. – jamesqf Apr 7 '15 at 4:03
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    @jamesqf I thought the whole point of this site was to discuss ways of improving the user experience. You could describe almost everything on here as "unnecessary" if you so choose. And thermostatic valves ARE safer because you can't go above a safe temperature without using an override facility. Also, as already pointed out, they aren't significantly more expensive - equivalent to $1 per year. I will update my answer with the water-saving potential later. – Lefty Apr 7 '15 at 6:20
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    @jamesqf: There are unfortunately two safety issues in direct contradiction. Legionella (Legionnaires' disease) is prevented by setting the hot water temperature well above the skin-safe level. – MSalters Apr 8 '15 at 11:35
2

Some systems in South America (called "calefón" in my country) require certain level of pressure to get the hot water running (for example, you can turn the knob 30º without the "calefon" getting activated in order change the water temperature), so in that case it's a device limitation.

enter image description here

1

In Australia, most showers have separate hot and cold knobs, and the more modern remainder are 'mixing batteries' like what tillinberlin describes.

There are some big UX problems with hot/cold taps:

  • When turning on the shower it takes time to adjust the taps to get the right temperature and pressure.

  • People must be taught to turn on the cold tap first and then the hot tap, to avoid scalding.

  • Sometime, rarely, in houses with low pressure the hot must be turned on first to get any hot water. Maybe this is because the pressure to hot water system drops too much if the cold is on first.

  • Usually the hot tap is on the left and the cold tap is on the right, but sometimes this is reversed! This often leads to the hot being accidentally turned on first, scalding the user.

There are some advantages to hot/cold taps though:

  • If you want a cold shower you only have to turn one knob. :P

  • The mechanism is simple with a very long life.

  • There is no little lag when changing the temperature.

To be honest, I never knew temperature/pressure knobs existed. Will be getting one for the new bathroom. TYSE!

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    Additional disadvantage: when you turn off the water for the soap and shampoo intermission, you will need some time and wasted water to find a good temperature again. – Crissov Apr 7 '15 at 9:56
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    Maybe I'm just jaded and "I see stupid people.", but there is little excuse for those that start the spray while they're under the target of the spray. Blindly, willfully trusting a system to not harm you (accidentally or via conspiracy) is unwise. When starting up a shower, I start up the hot flow (takes a little while to get through the pipes) then possibly dial back the hot flow and then add cold to it (increasing pressure somewhat) and decreasing total temperature. Only once I've dialed in the flow and temperature I want do I get under the spray. Backwards is... backwards. – killermist Apr 8 '15 at 12:27
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    A human's experience, having ever dealt with "water that is too hot" should have instilled in that person a respect for hot water. The most dangerous tool is a dull tool, because it isn't respected for the danger it presents. I personally think that "temperature and pressure" automatic controls shield the user from reality, dumbing the user down, and based on that I must state in no unclear terms that I think they are a "bad idea". – killermist Apr 8 '15 at 12:41
  • @killermist Maybe not jaded, just lacking in imagination or experience? Some showers are quite small, like the one in the house I'm in now, and I have to be inside it to turn it on. So if I turn the hot on too much I have to stand on tip toes up against the wall. Turning on the cold first and then hot is the opposite of trusting the system. The state where I live must also believe it is a problem as they have mandated a maximum temperature for hot water systems. – geometrikal Apr 10 '15 at 1:01
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    Oh yeah, because "thinking for yourself" will stop inertia so you are not flung out of your car in a collision... /s – MKII Aug 6 '15 at 10:06
1

While most countries have the mechanical knob as mentioned in all the other comments, Japan in fact, does have the option to control the water temperature and quantity.

You can even set an alarm that rings when your water has reached the desired temperature.

As for quantity and relatively pressure control, the toilets give you the option to select between three settings; low medium high.

enter image description here

0

This question assumes that “temperature” and “quantity” knobs are easier to use.

And yes, those types of controls are easier to use for me at least, but for my elderly mother, those types of controls have never been easy to use.

My mother could never tell which knob was for pressure and which knob was for the temperature. Part of the problem I think is that these types of controls are not all uniformly identical. I suppose that the shower fixture that cost $350+ would probably work for everyone, but the problem is that not everyone is willing to spend that much money on a shower fixture.

So when confronted with that choice at the store when you're already over-budget on your bathroom renovation, it's sometimes just easier to go for the cheapest $69 model (with only a 2.8 stars rating and mostly bad customer reviews) just to get the job done.

  • 1
    This sounds like the “The Edsel was terrible, so let’s just not have cars” argument.  There are two questions: (1) should the controls be for Hot and Cold, or should they be for Temperature and ‘Quantity’ (i.e., pressure, volume, or flow rate)?  And (2) if they are Temperature and Pressure, how should they be designed?  … … (BTW, as H2CO3 pointed out, question 1 is essentially equivalent to “Should we use Cartesian coordinates or polar coordinates?”)  … (Cont’d) – Scott Apr 7 '15 at 4:45
  • (Cont’d) …  Regarding question 2: two identical knobs side-by-side may be the worst possible design.  tillinberlin’s answer shows a faucet with a “hand gear” that you move left for hot, right for cold, up for more water, and down for less.  (I suggest that “handle” or “lever” might be a better term; its functionality is very similar to that of a joystick.)  … (Cont’d) – Scott Apr 7 '15 at 4:47
  • (Cont’d) …  Here is a similar one, with a knob that you turn counter-clockwise for hot and clockwise for cold, and push it backwards (away from you) for more water and pull it toward you for less.  This could be translated into a wall-mounted knob that would be suitable for use in a shower.  I believe that such a design (interface) would be reasonably easy to learn. – Scott Apr 7 '15 at 4:47
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    @Scott: No, it's more like the "manual heater & audio controls work just fine, and provide tactile feedback, so why should I have to do everything on a touchscreen that forces me to take my attention away from the road?" argument. – jamesqf Apr 8 '15 at 19:07
  • @jamesqf So true! If it were up to me, using touch screens for these things would be banned! Insane design to change something as simple as turning a knob to something you have to look at to control... in a car! – Stijn de Witt Jul 22 '15 at 23:07
0

Why? Because of all sorts of reasons outside of UX.

But I'd ask the reverse...why would you have both a temperature and quantity option? When showering, there usually isn't a gradient of amount. It's either on or off. No real need for a spectrum there.

As for temp, temp is created by adjusting the individual amount of cold and hot. In otherwords, the temperature is the 'quantity' variable. There is no temperature control. One merely is controlling the quantity.

This is a necessity throughout history as plumbing has mostly always been analog.

Now in the age of digital, your suggestion may make a whole lot more sense. But it simply didn't make sense with an analog valve system.

0

In Britain, at least, there are architectural/plumbing issues in the past that we had to deal with. This guy explains it better than I could: https://youtu.be/HfHgUu_8KgA

-1

It is funny that there are so many answers to this question without getting one that has to do with the actual function of a shower valve.

Let's go over the 3 examples that we have as examples already:

1.

enter image description here

This shower system has electronic mechanisms to calibrate the temperature and flow. The pros include easy user interface, looks cool (maybe because its different), and allows user to turn a little knob.

The cons are many though. First this must be calibrated correctly. After calibration the systems hot/cold water flow is changed it will become uncalibrated. Also what if you favorite temperature is between two of the settings? Now you are either a little too hot or a little too cold. And then the most obvious thing is cost/repairs. The low end ones I have seen are $500 plus compared to $50 for a more traditional setup.

2.

enter image description here

I kept the image even though a don't agree with it. Most modern versions of this have a decent size comfortable zone and this is adjustable. Note that in the application the water will divert through one valve like, the same as example 1. The water will be mixed together before being shot out. The pros include familiarity, ease of use, and the ability to tune your temperature tighter.

The biggest con with these is that most do not come with any sort of flow rate control. It is either on or off. The anti-scald mechanism is another feature that these have and not sure if it is a pro or a con - to some it will be one and to others the opposite. I for one like to be able to set the temperature as high as I want - especially useful when cleaning. The last con also has to do with the anti-scald mechanism. When the flow rate is decreased (think toilet flushing or someone doing the laundry) the valve will automatically process slower to reduce chance for temp changes. Which means you get a limp shower for a few minutes.

3. Good old knobs. The key to the knobs is that they do not (normally) have a shared mixing valve. Each operate independently of one another. The pros include they are cheap, they are intuitively easy to use (other than some people have hot on the left), only with knobs can you get the EXACT TEMPERATURE AND FLOW, and they are easy/cheap to install.

There are many cons on the knob side either. Some may say how they look, but I have seen some cool knobs. Another would be that you have to turn two separate things. If you have children the fact that there is no anti-scald mechanism is a con. Children can turn knobs and burn themselves easier. However the fatal flaw of the knobs is that you don't know what you get until you get it. You turn the hot and cold and just guess that the temperature might be right. You feel the water and adjust until it is right and continue to do so every shower there after.

Which is the best? Each of these choices offers different levels of work, different levels on install money, and different levels of controlability by the end user. Like any UX question, design should not trump functionality.

  • 3
    Niggle: I have a shower like your example 1, and it's neither electric nor does it feature discrete temperatures: it's got a mechanical thermostat that maintains the correct water temperature even if the pressures change, and the temperature selector is analogue. What it isn't is calibrated, but that's not so important to me. – Andrew Aylett Apr 6 '15 at 19:27
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    Sorry, but you're completely wrong about what you've listed as "system 1". First, it requires no calibration at all: it just uses a bimetallic strip to measure the temperature of the outflow and compares that to the requested temperature. It's a completely mechanical system that needs no calibration by the user, let alone recalibration. Second, there's no such thing as "between two settings". The control is a continuously variable dial. If you want it a fraction colder, just turn it a tiny amount towards "cold". – David Richerby Apr 6 '15 at 19:27
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    Also, what you don't mention about "good old knobs" is that it's impossible to alter the flow and the temperature independently. You can only increase the temperature by increasing the hot flow or decreasing the cold flow, either of which changes flow. If you want to change the flow while keeping the temperature constant, you have to change both hot and cold in exactly the right ratio. OK, it doesn't matter if you change the flow a little bit while you change temperature (or vice-versa) but separate controls for flow and temperature make this trivial. – David Richerby Apr 6 '15 at 19:30
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    The one in the picture comes with rate flow. The "SHR" setting at the bottom has "Lo" and "Hi" indicating the rate flow. I've never seen one that doesn't come with some sort of rate flow. – Stephen Ostermiller Apr 7 '15 at 13:46
  • 1
    Wow, the description for no.1 is wrong in so many ways it would be more helpful if it wasn't there. – Lefty Apr 10 '15 at 6:15

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