Why do showers have "hot" and "cold" knobs rather than "temperature" and "quantity" knobs?

  • 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.

    To match the taps on sinks, I guess. Also, many showers do have temp/strength controls.

    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.

    @SteveJones then why do sinks have hot/cold controls? Same issue.

    I agree the premise of the question is flawed. You are assuming prevalence one particular design but I see no evidence of that.

    @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.

    Where I live I have not seen many hot/cold knobs, all those have either temp+strength or only temp (with auto flow start/stop). I know it's not like this all over the world and in some places for some strange reason people still install new hot/cold screws instead of steadily available thermostatic taps.

    I've never seen hot/cold knobs on a shower (living in the eastern US); showers I've seen have all either had independent temperature and strength (although temperature doesn't give you an actual *temperature*, just a generic range from cold to hot) or a single control for temperature (that also controls flow, though that's pretty much constant once it's on)

    As another point on the legacy aspect, in https://www.youtube.com/watch?v=HfHgUu_8KgA, Tom Scott explains why until relatively recently many British houses had to have separate faucets for hot and cold water. He doesn't discuss what that means for showers, though, come to think of it.

    @usr I have seen both sets of controls so one is not more common than the other. This whole question is ludicrous anway, IMHO, as there isn't one way that is common and another way that is better. There are two common ways, each with advantages and disadvantages.

    Why do mathematicians use Cartesian coordinates (x and y extent) "rather than" polar coordinates (angle and magnitude)? Both have their legitimate use case.

    Because that is how it works in the background. We have simply not adopted, to any large degree, any levels of abstraction on top of our hot and cold water pipes.

    It’s also an accessibility issue. If a person has only one usable hand, and he’s using a shower with Hot and Cold knobs, he cannot change the water pressure without changing the temperature and then changing it back.

    I'm voting to close this question as off-topic because like many 'object' questions on here it's not about UX but much broader product issues (cost, manufacturing, history, etc.)

    Most tap in Italy would be the "mixer" type, unless the house is really really old. Bit disappointed to see that in UK are still widely used.

    I used to live in a house that had two taps on the shower that looked like regular taps, except one was pressure and the other temperature. It caused no end of confusion for guests not to mention embarrassment when we'd have to explain to them how to work the shower.

    For hysterical raisins!

    Where is the ancient hot/cold knobs most common? I almost never see this in Europe except in very old buildings with original plumbing. Almost all showers in Europe have a pressure dial and a mechanical thermostat dial usually with a anti scald feature (disableable using a button) preventing you to use temperatures above 40 C.

    Actually, I cant imagine the ancient hot/cold knobs is allowed in new buildings in Norway (possibly in the EU too). Never seen them in house built in after 1990...

    @SteinG.Strindhaug Separate hot and cold taps are still fairly common in Southern Africa, particularly in houses built before the 1990s (not so much in hotels, though).

    @SteinG.Strindhaug I'm from Poland, I've been on vacations in Croatia, Bulgaria, Greece, Tunisia, Turkey... And this question is the first time I see "temperature and quantity" controls.

    This is pretty much the "RGB vs. HSV/HSL" debate all over again. ;)

    I also *very* rarely see hot/cold knobs on showers (Northeast US, but even all throughout the US). Most I see are either the type where you don't really adjust pressure, just temperature (you turn it on it comes all the way on cold then the more you turn the hotter it gets), or the handle style where rotating is temperature and pulling is pressure. So this is kind of a strange question to me. The only time I see separate hot/cold knobs in showers is in old (> 50-60 yr) hotels and houses, or in more "thrown together" type situations where on-hand parts were used for plumbing.

  • tohster

    tohster Correct answer

    6 years ago

    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:

    The type of shower control pictured is also normal here in the UK.

    I'm not from the US, and the one in the picture (or similar ones) are the only knobs I've ever seen

    japan? That's really funny – my parents have 'exactly' the same, made by german company GROHE

    That's also very common in Germany, too. Got mine in the shower last month.

    Comments are not for extended discussion; this conversation has been moved to chat.

    The specific heat capacity is not relevant here - we can assume the only method of altering the temperature of a partly-drawn bath is by adding more hot or cold water, and then the resulting temperature is just a linear combination of the hot and cold water temperatures. This would be the same almost regardless of the specific heat capacity. Baths are hard to warm up because the hot water is only 15-20C hotter than the target temperature, and the cold water is often ~25C below it. With boiling water it is much easier to warm up a bath.

    @PhilH specific heat is relevant because hot/cold mix is not the only way to get the right temperature. Many users draw a hot bath and wait for it to get to the right temperature before jumping in.

    "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.

    This is not *nearly* as rare as you make it out to be, and it really *doesn’t* require expensive or complicated electromechanical feedback. *That* certainly is expensive (and very nice), but less sophisticated pressure/temperature controls certainly exist, which are purely mechanical and, while more expensive than hot/cold, are still much closer to hot/cold in cost and complexity than the faucet you describe.

    @AE Do you happen to know if there are regional trends for this sort of thing? In the west midlands I've never seen any like the type pictured. Pretty much all the showers I've used in the west midlands have had one dial for "hot, cold, economy" and one for relative temperature.

    @tohster, +1 for the jab at qwerty. Are you by any chance a Dvorak typist? If so, I'd like to chat with you (see my contact info on my user info page).

    @Pharap, ah, sounds like an electric shower. Where the water is heated at the shower itself. Less plumbing (only one pipe), more wiring. Could well be to do with the type of house and the existing plumbing - and the housing stock definitely does vary by region - as well as the time period when the shower was installed.

    These types are form like the 70ies or 80ies? I'm from western europe (Netherlands) All sinks and taps everywhere have the pressure/temprature controls. Facets on sinks are mostly from left to right and up and down controlled however so no exact temp. I think it depends also on the amount of pressure of the water, if it fluctuates a lot the heat/pressure thing might not work as expected so you need a good supply which you can count on.

    IMO this answer contradicts itself (unless that AWESOME faucet has electromechanical feedback and/or thermostat adjustment, which having bought something similar I am pretty sure its doesn't) and the comments confirm that impression. Concretely, those nifty knobs are just a mechanical wrapper interface to separate internal valves controlling hot and cold water flows. Upon changing the external conditions (most relevantly hot water temperature, water pressure) it will probably do little to compensate. In any case I have experienced the 38°C stop does not always correspond to that temperature.

    hi @MarcvanLeeuwen the valves actual do use either mechanical or electro-mechanical feedback loops to adjust for changes in water pressure or temperature. This brochure from Delta Faucet shows how the mechanical versions work. They are subject to calibration error, so if the calibration weakens the cartridge needs to be replaced. Hope that helps.

    :O I'm from Australia and I have never once seen a shower tap/interface like this! (and I've showered in a lot of houses) On the one hand I'm astounded that anyone would find it difficult or unpleasant to control hot and cold individually (it's so incredibly easy and totally normal), but on the other hand I think a pressure/temperature control like this is a fantastic idea and I want one (and then I hate myself for wanting it because I feel like I'm joining the throngs of lazy, ignorant people that infest the world, even if that feeling has no rational grounds).

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Content dated before 7/24/2021 11:53 AM