A Call For Better Shower Temperature Controls

A good shower is a beautiful, rejuvenating experience. Contrarily, a shower that’s either too hot or too cold becomes a harrowing trial of endurance. [Ben Holmen] has been musing on the way we control temperature in our showers, and he has come to the conclusion that it’s not good enough. He’s done the math, quantified the problem, and is calling for better solutions for all.

[Ben]’s plot of shower temperature vs. mixer tap angle.
[Ben]’s complaint rests with the mixer taps that have become the norm in modern shower installations. These taps have a 180-degree range of motion. On one end, you get maximum cold water output, on the other, maximum hot water output. This is fine for a kitchen sink where we often want one extreme or the other, and exact temperature isn’t important. However, for a shower, it’s terrible.

By [Ben]’s measurements, just a 10-degree range on his own shower tap corresponds to comfortable, usable temperatures. That’s means just 5.6% of the control range is devoted to temperatures the user is likely to select. His argument goes that this is the opposite of how it should work, and that most of the tap’s range should be dedicated to comfortable temperatures.

Ideal water temperature curve, compared to standard tap.

This would allow much finer control of shower temperature in the actual useful range. It would allow us to make tweaks to our shower temperature without having to ever-so-delicately nudge the mixer tap. Extreme hot and extreme cold temperatures should still be available, but left at the utter extremes.

Sadly, [Ben] doesn’t work for Big Tap, so he can’t directly influence the product sold to the public. Instead, he’s calling for manufacturers to develop shower valves that prioritize the temperatures that humans desire most. Unfortunately, it’s not immediately clear how the mechanics of such a valve would work without adding considerable cost and complexity when compared to the traditional model.

What do you think? Are things fine the way they are, or does [Ben] have a point? Perhaps you’re a two-tap evangelist! In any case, we’d love to hear your comments below. Meanwhile, if you’re more worried about the water bill than the temperature, we can help you there as well!

144 thoughts on “A Call For Better Shower Temperature Controls

        1. Maybe not ‘soluble’ in the strict chemical sense but certainly ‘soluble’ in the everyday sense, meaning, ‘easier to get off the surface’. Same applies e.g. to oil in the pan: you can’t argue with a person washing lots of dishes that greasy stuff is better handled with warm or hot water, and they may call that ‘better soluble’ although that’s not what’s happening in the strict sense.

          1. I would agree with you here. Unfortunately people tend to be pedantic, almost binary in right or wrong, especially in the comments section. End of the day, warm water dissolves and suspends more readily than cold.

  1. Obviously he has a point but it’s rather useless without a solution. The people who design mixer taps would make better ones if it was easy.

    Ones with separate hot/cold taps are much easier to tune.

      1. When the thermostatic mixers work, they’re great. Unfortunately, the thermostatic mixer cartridge in my shower lasts about 6 months and then fails at some arbitrary mix point. Sometimes it is hot, sometimes cold. Costs $170 a pop (from a distributor) and the company has since gone out of business so at some point the supply of those will dry up. Then I get to spend thousands redoing my shower tile. So, yeah, thermostatic mixers are great…

          1. It came with the house. You just don’t think about that sort of thing when doing a home inspection. One of a small army of things the seller failed to disclose but I still love my house now that it looks nothing like what we bought!

        1. My house came with Delta Monitor pressure-balancing thermostatic mixers, I’ve lived here for a decade, and they haven’t needed any maintenance.

          Are yours a different brand, or are the temperature-balancing ones just more finicky?

          They do suffer from the narrow-usable-range problem described in the article, but since they’re (almost) set-and-forget, it’s no big deal.

          And the temperature stays consistent no matter what the washing machine is doing. That’s the best part.

    1. Honeywell, Johnson Controls, Bray, plenty of companies make globe valves with linear or nonlinear valve configurations as options. Control valves for process or HVAC have to be selected carefully by CV and curve so that automation can tune a PID loop on them. Steam coils are a real pain to tune, especially when the media accepting the heat has a varying delta T. But the non linear curves of 3Way diverting valves give you a nice fat dip in the middle where it takes a lot of stem travel to drastically change the ratio of the ports feeding the common, and really sharp drop offs at the ends where it’s 100% A or B to AB. A Honeywell T775 controller can be picked up for a couple hundred bucks that can be fine tuned down to 100ths of a degree. And they have a digital input to create a setback temperature setpoint. Person A likes discharge setpoint 110F, Person B likes 115.55, simple two position switch on the wall keeps both people from tinkering with the others settings. Run the valve feed through a High limit switch set to 120F, have the actuator spring return 100% cold, no boiled faces. The T775s have a long term memory, so if you have seasonal dips in your cold water supply, they accelerate the PID for output rise, and decelerate the PID for output drop in cold months, reverse in warm.

      1. I’ve frequently dreamed of doing something like this. I’m a controls systems engineer with 20 years of field and consulting experience, so am quite capable, just haven’t had the motivation.

        My imagination is to have a display mounted on the wall showing setpoint and current temperature with either momentary buttons or a rotary dial for temp setpoint control. My only unknown is how would you measure temperature? A strap on sensor or immersion? I’m not familiar with any immersion sensors that go that small but I also haven’t researched it.

  2. it may be only 10 degrees for him, but the comfort zones for my girlfriend and me most certainly don’t overlap. Her comfort zone is “are you trying to freeze my balls off” for me, why my comfort zone is the fires of hell for her.

    Besides, this has been solved decades ago with thermostat mixer taps.

    1. Make that the other way around over here, my fiancee always thinks i want to melt his skin off when he doesn’t set the shower to his needs after i was in there while i set our gas “Durchlauferhitzer” to Bring It On.

  3. Since our warm tap water can be anything between 10-95°C I apprechiate the mixer taps which I basically have set to the personal maximum comfort temperature. I agree with it would be more handy to have higher resolution in the comfort temperature range but if you have some tinker-feeling in your fingers even the standard mixer tabps allow more than enough adjustment. If you can finger you can also adjust the tap water properly.

    1. Yikes, wonder how much thermal energy you’re loosing in the pipes when the water temperature is above 50°C.
      You should look into those thermostatic valves that attach to the boiler output.

      1. 60°C or above is often building code for warm water for hygiene reasons. Plenty of bacteria will thrive inside your pipes and the large tank otherwise, rendering any mix with warm water unsafe for consumption.

        1. That only really applies to the boiler itself, to prevent the growth of Legionella. If it applied to the pipes, you’d have to run the cold water supply at that temperature, which obviously does not make any sense.

        1. Western Europe.
          Most hotels have them, and if a house was built <5 years ago, chances are it has this too.
          (Unless someone really wanted to save money short therm.)

          For older houses, there are specialised bathroom renovation companies, that upgrade your old bathroom to modern comfort standards and those are very likely to propose such an upgrade as well.

          Once you are used to such a system, you don't want to go back and word of mouth spreads quickly.

      1. You must have a very different idea of cheap than I do. Looking on the Lowe’s and Home Depot sites, the starting price for one of these setups seems to be $400 – $500.

        We won’t even take into account the cost of potentially blowing out the shower wall to install it.

        1. Poor merians, mine cost me 80 bux from IKEA, vallamosse https://www.ikea.com/nl/nl/p/vallamosse-thermostaatmengkraan-voor-douche-verchroomd-10349655/

          Fits on a ‘standard’ connector too. As others have mentioned, decades old tech, very common here.

          Same goes for toilets, most modern bathrooms have hanging toilets with built in reservoirs, but american bathrooms all look the same and often work poorly too (had to often replace the insides of tanks in the US ..)

          1. It is “standard” in Europe to have the valves outside of the wall, but not in the US. i.e. the hot pipe and cold pipe just stick out, and everything (the valves, the vertical pipe for the shower head, etc) are all outside of the wall. It’s tidier having all the plumbing inside the wall, but it’s worse when there’s a leak or you need to replace the valve body. With my Grohe valve set, I can easily replace the cartridge, but none of the pipes.

          2. @kjw not sure what you are talking about. Water pipes (hot and cold) are inside the walls. The only thing that pokes out is the 150mm spaced hot/cold screw terminals. Granted from there on you have an external shower.

            Still very common, just more expensive is that you only have the knob and the showerhead sticking out of the wall.hotels often have this too. And yes, also these have themalmixing.

            So this is a completely solved problem, for more the 30? Years?

          3. What I mean is that style of faucet where the hot and cold pipes stick out from the wall is pretty rare to find in bathrooms in the US. In europe; I’ve never seen it. Kitchen faucets do come in that style, but it’s the two valve that isn’t allowed in baths anymore. I guess my point is that I can’t retrofit my US bathroom with that style of faucet; I don’t have the pipes sticking out from the wall. Instead, all the mechanicals are hidden inside the wall, and only the handles, spigot, and shower head(s) are outside of the wall.

      1. For many cases you’ve got to remember most of the housing stock in the USA is old. I’ve never lived in a house built more recently than the 60’s.

        Repair, which is common, wouldn’t involve updating (often with other people; I like arc free wiring). New builds here tend to have much of the new tech but with the attached price.

        One of the reasons why there’s such a variance in home prices between here and other similar countries I assume.

  4. > it’s not immediately clear how the mechanics of such a valve would work without adding considerable cost and complexity

    The lever turns a screw which moves a needle valve. The temperature is regulated by a wax capsule that expands from heat, so it pushes the needle down. When the capsule is moved further back, the temperature can rise higher.

    So, the obvious solution is a double screw, one inside the other with a finer pitch. The outer screw turns for coarse adjustment and the inner screw turns for fine adjustment.

    1. A lot of mixer taps don’t use needle vales though.

      A rather common method is two ceramic plates that in turn have milled out channels. The plates are free to slide on top of each other. One is affixed to the base, while the other plate is moved by the handle on the faucet. Depending on how the plates aligns, one will get different amounts of flow from the warm and cold side.

      1. The temperature of the cold side of the faucet changes with the seasons – and by how long you’ve been running the tap – and the hot side changes depending on your boiler temperature – how much hot water you’ve used already – so if the faucet only adjusts the mixing ratio then it’s mission impossible. Your “fine adjustment” will be continuously drifting.

        This is why showers use the wax capsule thermostats instead.

  5. The electric water heater in my apartment heats with constant power (and has four settings to select from).
    One conclusion from this is that the ratio between hot and cold water at the tap does not influence the temperature (as long as the pressure drop is high enough to keep the heater on). It’s the amount of water I draw per time that decides the °C added by the heater.

    My shower has a single handle for the mixer. Rotate to select the ratio between hot and cold. Tilt to increase the flow. I use it exclusively on the “hot water only” end and tilt it to change the temperature. For me it would be ideal to have two valves with multiple turns to control hot and cold water separately. But I won’t replace the mixer or heater in a rented apartment.

    1. When we remodeled one of our bathrooms a few years ago, we were told that using 2 valves (one for Hot, the other for Cold) was now illegal, so they wouldn’t accommodate my request.
      I’m guessing that is a USA law.

        1. I guess this is a result of the “anti scald” code requirements. Some people set their hot water tank to a higher temperature (160F, 71C) in order to have “more” hot water. In a configuration like this, if you only turn the hot tap on without scald protection devices, you can get 3rd degree burns in less than 2 seconds. 3rd degree burns are so severe that they typically require skin grafts. These rules are not restricted to the US; the UK has required anti-scald devices for baths since 2006. Check your own local rules.

          1. …and rightly so, given that burn injuries like these are not only painful and cosmetically damaging: they can be fatal to the elderly. Homes need to be designed to cater for a wide range of inhabitants and avoid being a death trap to visitors as well.

    2. I have instant water heater than runs on gas, installed outside each bathroom ( in open air) . I set its temperature to comfortable and turn the shower tap to maximum hot. So its always comfortable hot and I don’t waste money on the heat that I am not going to use.

    3. I have that in an old bath. 1/2 turn on hot, 1/4 turn on cold is perfect. The single knob ones are cold, cold, cold, cold, cold, still cold, a little warm, just right, HOT.

  6. Mine (I had to take it apart) has a pressure balancing element which attempts to equalise the pressure from the hot and cold feeds. Unfortubately, this design has a tendency for this element to freeze in place due to mineral deposits. Mine has.
    It’s a big job requiring an expensive specialised tool to remove the jammed element, so I haven’t. Likewise, replacing the entire valve requires tearing into a wall, so that’s not happening either.
    Fortunately, the balancing element has frozen itself in a middle position, so water temperature control is still functional, I’ve just lost the balancing feature, which isn’t that much of a problem (but annoying, nonetheless)

    1. Thank you. Perhaps this explains my problem. The landlord is not happy with me complaining that the water temperature fluctuates even after replacing the cartridge. (Flush the toilet, shower goes cold. Run the dishwasher, shower goes cold. When the other draw stops, shower goes briefly hot.

      1. That means your water pipes were probably not designed but just connected with a “hope-for-the-best”-mindset.
        Same goes for the drains. Clogged drains or slurping noises are a solved problem. You just need to follow some simple guidelines and not just connect pipes randomly.

        Some thechnology also has requirements, such as filters to ensure no small particles make it up into the mechanics.

    2. I would look at the valve and brand. I thought mine was this and it turned out to be a modular cartridge which only needed a shut off of water, removal of the handle and valve cover and then swap out of the cartridge followed by reverse assembly. YouTube had several videos.

    3. Mine’s a Moen. Apparently, they’re known for this balancing device’s tendency to freeze up. There’s a retired plumber who sells a special pair of pliers to extract the balancing device, but I decided to let “sleeping dogs lie”, after replacing the cartridge and restoring smooth operation to the control.

      1. I have had considerable troubles removing Moen cartridges.
        When one of our bathrooms was remodeled a few years ago, I asked the remodeler to not use Moen.
        But my wife liked the look of the fixtures.

  7. My worry with this is when the shower is a distance away from the HW source, (unless theres a thermostatic element behind the scenes that does this anyway… AIUI, the thermostatic element in most showers only modulates it a small amount either side of the set temperature) sticking it on full hot is the best way to get maximum flow down the HW line, and therefore quickest time to usable shower

        1. Every nation passes tons of dumb laws, yours as well.
          Every law is one step away from freedom.
          The better a nation’s culture understands this, the better their government will be.
          This is why California is what it is.

          1. People having showers isn’t the major reason for water shortages. Household water usage in places like California accounts for about 10% of the total water use, and the water saving efforts have managed to decrease it by about a fifth since the 90’s, which basically means jack s***. It’s just two percentage points less.

            What’s happening is a “Do something!” panic. People vote in politicians who write draconian laws that feel effective because they’re punishing the voters directly – but actually these laws don’t change the situation in any meaningful way. Because the situation is not resolved, the politicians escalate their game and people vote them all the more: “We must do something! This is something! Therefore we must do this!”

            That’s is actually how you build a career in politics: by continuously failing the task you’re appointed, while making it look like you’re the only one doing something about it.

          2. Cherry picking statistics is fun!

            Water is a finite resource. We can’t just build a factory and produce more water. To enable continued growth, more efficient use is required.


            “Despite population growth, total urban water use has fallen” – Decreasing water use per person also means that you can build denser without having to install larger water mains or new water treatment plants.

            “Agricultural water use is falling, while the economic value of farm production is growing” – Flood irrigation is simple, but wastes a lot of water. Many orchards and fields around me have converted to subsurface watering; far less evaporation loss than a giant sprinkler.

            Less water per shower also means less energy used to heat the water (which largely goes down the drain)

          3. >To enable continued growth, more efficient use is required.

            Continuously growing demand without increasing supply spells poverty and shortages anyways, despite your efforts at improving efficiency. It can’t be sustained.

  8. The range of adjustment needs to allow for significantly different supply temperatures.
    While my hot water is pretty constant, once it gets to the shower (Ben’s comment above), the cold water is not. In the summer, cold water can be 15°C, in the winter 3-4°C. This means that a summer shower has the knob at 1:30-1:45 (analogue clock), and in winter at 11:00. As the max cold / hot are at 3:00 & 9:00, the winter / summer difference is pretty large.

  9. You know you can change the temperature by adjusting the hot and cold values with a screwdriver on the value. If you want less range reduce one of them. if they are both 100% on you get a small comfort zone, if one is 50% on and the other is 100% on then you should have doubled the comfort zone to 20%. Reduce the Hot so you don’t burn yourself then the top of the range should have more options for comfort.

  10. I built a “thermostatic mixer” which used a bimetalic strip that controlled the hot-to-cold ratio. It maintained a stable temperature of water even while waiting for the hot water from the hot water heater on the other side of the house (once it became just warm, before full flow) and maintained temperature as the water heater ran out of hot water and it’s output temp decreased.
    It worked pretty well and as intended. Alas, with my small workshop and limited tools I was never able to make one that didn’t leak.

    1. making things waterproof / watertight is hard, especially when you have moving parts. Whole careers are built doing only this! One trick that you might have overlooked: once you have the proper size and shape channels for o-rings, you need to lubricate them!

    2. There are commercial products that do this kind of thing.

      I know it’s hard to buy what you want to build, but this might be one of those times. :)

      They come in two varieties: temperature balancing, which is basically what you just described, and pressure balancing, which doesn’t actively adjust the temperature per se, but which responds in real-time to pressure variations such you get when a washing machine is going through its cycle.

      My house has the latter, and I’m grateful for it every time I return from mountain biking, throw my dirty clothes in the washer, hop in the shower, and notice the pressure wavering at a constant temperature. :)

      1. I built it mostly as a “Because I can” type project, and wanted to see if my bimetalic strip idea could properly adjust the 2 valves. All analog mechanical, no electronics. I built 4 iterations of it before I quit. Mostly because I found a bunch of commercial versions (although all rather expensive) and I also next wanted to try an Arduino controlled version with display, setting for different family members, etc. I never did get around to making a digital version. The final analog version was huge because it needed several large bi-metalic sheets to have the ooomph to move the valves enough. It worked quite well (except for leaks) and kept a very stable temperature tho, even through pressure changes and dwindling supply from the water heater. Also had to quit because my sister insisted I patch the giant hole in the wall where I was tinkering with it. Didn’t think that was quite fair since the hole was on the opposite side, in MY bedroom!

  11. I think he should be grateful for 10°.
    I’m pretty sure my shower has a usable adjustment range of less than 2°. And the precise location is different on a daily basis.
    (Multi-storey apartment building)

  12. Ok, people this is Hackay — The author has presented a problem, someone should respond with a digital programmable solution.
    Microcontroller, thermistor, digital readout, limiter (max temp to prevent scalding)
    Allow presets
    Mom, Dad, Sis, Bro, Mom &Dad etc allow at least 20 presets maybe set by a assigned number Kids might not want to see an option as they scroll thru for mom and dad or even older bro and gf.
    Walk up to shower select preset hit go.

    This would be a great write up for Hackaday

    Now to the people that are going to say, well do it. At this point in life it doesn’t apply to me. I’m old, I live alone and my setting for the shower is Full-on hot water, maybe a little less if I want a longer shower without running out of hot water.

      1. Maybe use the astable mode with a potentiometer between Vcc and Discharge? The Control input would be from a voltage divider with a thermistor.

        Just random thoughts from memory using 555s. Maybe looking at the data sheet would help…

    1. Sounds like a job for a pair of servo-controlled valves and a thermistor. And a digital display with temperature, or a RGB LED for indication the water is or is not what it should be.

      Servo valves, if they can withstand the pressure, can be “borrowed” from digital heating-control valves. If not, a suitable torque servo can be used. Preferably with a knob/lever on the shaft so there is a manual override in case something somewhere fails.

      Manual overrides are generally a good idea. Smart switch? Add a 3-position mechanical one so it is on/off/auto. Bugs happen and in complex systems it is only a matter of time when something somewhere dies.

  13. Outgoing temp is a factor of incoming temp which changes house to house and month to month and also depending on other taps being used concurrently.
    Person to person this 10% range varies wildly as well.
    But another big issue is getting flow right at a set temp, especially if you’re using more than 1 shower head.

    The right answer is for all the complexity, just make digital shower thermostats standard. Use a 2 flow system with solenoids and a cheap control panel. This can’t be much more expensive than a complex mixing valve. There are kits under $400. Standardizing the components could make them significantly cheaper. They also would benefit in lower water usage for most showers allowing the temp to be maintained while lowering presssure while sudsing up, timed showers, auto-cutoff while warming up, etc. we should mandate these features for water control.

  14. I would pay hundreds of dollars for a shower valve that actually solved this! *Insert take my money meme*

    One challenge is that different houses will have different baselines for too hot or too cold depending on their water source and their water heater. So, you’d almost have to have some sort of hidden tuning knob to dial in where that comfort zone exists.

      1. For example, A search for “thermostatic grohe cartridge” (assumes you have the existing valve set, just need to swap out the cartridge) will only cost you $200 or so. However, if you need a new valve set (the body into which the cartridge is installed), you need to remodel the whole bathroom, because you have to tear the wall open to replace the valve body. Good luck!

  15. At my old house, the shower valve had a tab that controlled the temperature separately from the pressure so you set the tab to the temp you prefer then never had to fiddle with it again, just turned on the shower and it was always the temp you set.

    1. I’d be surprised that pressure valve is like a stereo volume control, 2 valves on one shaft. When the mixed flow from a shower is shut off with the single valve for longer than seconds hot water may back-flow down the cold side back all the way to the water heater. It’s near impossible to find a mixing valve that has check valves to stop this. In a flat this may not happen but a basement water heater will set up a gravity thermal flow and hot water will come out of the cold taps. A ball in the hot side of the mixing valve would stop this and allow a single button on a shower hose spray to conserve water and heat while shampooing etc.

      Saving resources is important now but convenience in design and ease of use have been deemed not important. 2 occluding round holes that slide past each other is good enough, it worked for the Romans. There probably is no valve that has a log taper like any volume pot. This design would make saving water when a trickle is enough but half way is nearly full on!

      More than a century ago the player piano had regulated pressure that when throttled controlled speed of the motor spooling the music. A slide valve over a trumpet (side view) shaped hole gave tempo control over a linear range from largo to presto in feet/beats per minute. A butterfly valve throttled our cars till fuel injection and still forms the air intake. Most cars are touchy at low speed as a result.

  16. I totally agree with this research, but I was really really hoping for an actual solution to the problem.
    There’s also the other type of taps that has a single lever that controls both the flow and the temperature. Those are even worse because if you change the flow you’re also changing the temperature…

    1. In the 5 hotels + one family I slept at in my recent USA trip, I found 7 different shower controls and had to ask front desk and/or uncle to explain me how they work 3 times.
      The worst was a shower knob that required a 1½ turn to give hot water with labels that did not suggest more than ½ was necessary.

      1. I once stayed at the Sofitel? near Chicago O’Hare.
        The faucets were marked C and F (no, not Celsius and Fahrenheit).
        I got slightly burned thinking C stood for Cold.
        (Chaud is French for Hot)

      2. I love visiting the USA but their plumbing is generally rubbish (in the 30 or so states I’ve visited.) I’ve hardly see two showers alike and every toilet needs multiple flushes to get rid of the waste.

  17. Mixers don’t address one key element: Control lag.
    Infact, mixers dictate that you not be able to address will control lag.
    My outdoor shower, yes it has hot water, has practically zero control lag. How? Simple. 2 taps one hot, one cold. But the pipes don’t join just after the taps. They continue on, and join right at the shower head.
    That way, a change in tap setting immediately alters the temperature.
    Zero lag. Tight control.

  18. Whoever invented the one knob shower control should be made to suffer unpleasant bathing experiences the rest of their existence.

    They took a perfectly fine thing and screwed it up for all eternity. I hate single knob mixing valves with a passion.

    1. I agree with KC. The other thing they have screwed up recently is these stupid “mirrored” taps, where one tap turns off clockwise, and the other anticlockwise. So instead of turning one tap off, you turn it full blast. Or vice versa!

      1. I recently replaced a shower valveset. It was a ceramic valve design which has basically two flat plates with a triangular opening which you could in theory rotate 360 degrees. It features a plastic spacer you could rotate to change the clockwise vs anti-clockwise behaviour of on/off. That’s one advantage to the ceramic design; there are no (metal) threads that are fixed for life, or require you to manufacture left and right-handed versions of the same valve.

  19. Has no one outside of Scandinavia heard of “thermostatic mixing valves”? I’ve been a few places outside Scandinavia it’s the same problem everywhere; Turn the two, wait for hot water, try to mix hot and cold for a reasonable temperature and shower before they boiler is empty.
    Scandinavia has the thermostatic mixer. Basically a bi-metallic spring opens and closes the hot and cold valves. The user just sets the desired temperature.

    1. These do exist in the US, but for some reasons they are relatively rare.

      I didn’t know what I was missing until I moved into my current house a decade ago. They might add a couple hundred dollars to the cost of a house, but they are absolutely worth it. If my next house doesn’t have them, I’ll spend whatever it takes to have them installed.

  20. Here in europe it’s common to have taps with two knobs. One knob for setting the flowrate, and another knob for the temperature, and this usually has a stop button for an “acceptable” shower temperature, and this works quite nicely. If you want to fill a bucket with hot water, you just push the knob and turn it further.

    To get an Idea of what they look like, I’ve added a link to a random hardware store

    Somewhat related to this, there are also local regulations. In his “boiler placement” video, Dave EEVBlog mentions there is some maximum water temperature for kitchen faucets. I was curious and measured mine at 78 degree centrigrade, which is more then (apparently) allowed for the upside down people.

    1. In .au a tempering valve is required, and is required to be adjusted so that no outlet has water hotter than 50C. Depending on the plumbing in one’s house, this might mean that one “hot” tap might deliver 50C water while one at the end of a long uninsulated copper pipe might be much cooler.

      These tempering valves are usually adjustable so you can manually alter this to, ahem, “compensate for long pipes.” So with a screwdriver, a thermometer and a bit of spare time and hot water you can usually adjust the tempering to a temperature you prefer. If you ask your plumber really nicely, they might also install a pipe upstream of the tempering valve so you can have one “really hot” tap. This is not compliant with any plumbing code so it’s up to you to make sure this tap is somewhere that unsuspecting visitors/children can’t hurt themselves

      Note that the hot water tank itself is also required to store water at >60C to prevent growth of legionella in the tank. Hence the requirement for a tempering valve to knock the temp back down before delivering it to your tap.

      To solve the original problem in the article, I kept the 1970s arrangement of two taps in my shower. One for hot, and one for cold. Each tap has about 270 degrees of adjustment, which is 540 total degrees of adjustment. The only “wear” item that will need replacing is a washer, which can be had for about 25c. My original washers from 2019 are still just fine.

  21. 1there is a number of things tha I;d want to touch as a former faucet engineer, but to keep this short, I’ll stay with two things
    1) two ocludng orifice approach is common and it works. ANd the don’t need to be round. Even more – manufacturers do their best maths to make temperature vs angle linear (e.g. https://kerox.hu/wp-content/uploads/2022/11/kn-35.pdf ). So it is quite clear how mechanics should work. The same, justa adjust the shapes

    2) there are already dozens of types and models of cartidges (e.g. https://kerox.hu/en/products/cartridges/ ). Most never made it to market, at least in company I used to work. Why? People don’t like to investigate taps. They should give water. And if customer will not get how the darn thing works at first glance – will not buy. ASking someone for something that is supposed to be simple would make them look stupid.

  22. Here in Japan, besides the thermostatic mixer valve, we also have a control panel on the wall in the bathroom (a full wet room seperate from the bathroom vanity area etc) where you set the exact temperature with one degree resolution.
    Start having a shower and it also automatically locks out the kitchen control panel too for safety.
    You can also press a button and walk away to automatically fill the bath and keep it warm with a recirculation pipe.

    It works really well, just set your temperature on the control panel and have a perfect shower.
    This has been the norm here for decades now.

  23. I’ve read all the comments…
    Although “thermostatic mixing valve” is obviously the correct answer, I’ll add a couple things missing.
    First, you can place a SINGLE TMV directly on your hotwater tank outlet. This regulates the maximum hot water temp for ALL showers. This increases the capacity of your hot water tank by allowing you to turn the tank temp up without worry of scalding (the TMV fails safe closed). It also means the full 180 degree valve setting is usable.
    Second, you can bypass the self-balancing feature of the mixing valve and add a ball valve to restrict the cold water supply to the shower. This significantly increases the usable lower end range.
    Third, add a recirculating pump and a timer. Doesn’t require any additional pipes run. It just pushes hot water through the hot lines and back to the tank through the cold lines, not down the drain. When you’re ready to use the shower the water will already be hot and no water wasted.

    1. Re: recirculating the hot water back to the water heater- I asked a plumber about that here in Oz and he looked at me like I was from Mars. Apparently not allowed by the antiquarian plumbing code here.

      1. Not surprised a plumber didn’t know about something. They have a hard enough time sweating pipes correctly. The twisted look on the plumbers face should tell you there’s no code even mentioning it.

        Neither the EU nor USA’s building code have anything preventing recirculation pumps.

        It’s about $300 and one to two hours to install. Low skill level DIY weekend project.

        1. What kind of recirculating system are you thinking of? The systems I’m familiar with require an extra pipe to be added, which usually means ripping up walls and floors/ceilings. Installing a new faucet on a sink is easy and doesn’t require ripping walls open. Adding a return pipe from the end of your system to the water heater does.

          1. Extra pipe isn’t needed. Someone in the 70s realized that the pump could simply push the warm water down the cold water supply line just as easily. Only requires a check valve. Since thermostatic valves are cheap, they added one of those too, so the check valve only allows hot water to flow when cold.
            Google hot water recirculating pump retrofit or Watts Premier Instant Hot Water Recirculating Pump System with Timer

  24. Wouldn’t adding a small single or multi-turns micro adjustment knob on the main valve be enough? Like for example having your 180° handle that match linearly the cold-hot extremes, and a smaller inner -150°..+150° knob to adjust in a +-5% relative range. I’m sure this already exists…

    This doesn’t fix non-lineartiy, but it at least adds more precision and contfol in the comfort zone. Of course, the equivalent cheaper solution could be to tie-wrap a 2′ spoke to the handle, or to install a nice and big ship wheel to steer away from the pain ^.^

  25. Wait. Nobody here has a temperature controlled water heater?

    Mine came with the house, is around two decades old, and has a small screen where you press buttons to set the temperature (in degrees). I am considering replacing it and am spoilt for choice with modern models.

    Set temperature, get in shower, set mixer tap to maximum hot. Done. It even limits adjustment when in use to prevent burning someone in the shower.

    Outdoor unit is about the size of a desktop laser printer.

    Is there something that prohibits these in the northern hemisphere?

    1. In the US, I think the biggest factor is that tank water heaters are CHEAP compared to tankless. Also, they function without electricity. Also bigger houses with multiple bathrooms means it’s more cost efficient to have a central shared water heater instead of one per room.

      1. I have a private house with two bathrooms, both getting hot water from one tankless heater.
        The temperature set most of the year is 45 degrees Celsius, and we use it to almost to the maximum hot.
        Once per year (usually at the end of heating season) we setup for over 60 degrees, run the hot water run to clean up the pipes, and off we go back to 45.
        I don’t understand why anything hotter than 48-50 C would be needed, if you need to mix in cold then you’re doing it wrong (or have really a lousy pressure).

  26. Potential solution: connect the hot line directly to shower tap and then put the valve on the cold line only to vary the amount. That way you’re only ever getting, at most, a 50-50 hot-cold mix. (I actually have no idea if this is feasible, I’m not a plumber)

  27. Over here in the UK thermostatic showers are normal.
    A typical one will have 2 control valves.
    Valve 1 goes from off to pressure washer jet
    Valve 2 goes from cold to 60C (normally with a stop at 40C that you have to push a button or something to go past)

    The whole thing adjusts automatically to changes in water pressure or temperature although it is slightly under damped

  28. This is a thought that has mesmerised me for years! whenever i am under te shower trying to adjust the right temp, i come back to this, but my knowledge of thermodynamics and time and time again of thinking about hits, got me to put down some equations about this. Basically the output temp will be the result of steady state entalpy balance on a open systen. This is are very simple equations, but by having a look at them you will realise that the linearityof your control on the output temp, depends a lot on the masss flow of hot water, cold water and the sum of them. At vely little flow, the system becomes more non-linear so to be able to tune it finely you need to put more mass flow through! Don’t worry, you dont need to waste water to get in to the stable region of the control. So I tried this on the shower many times and it helps! Having said that, I totally agree that current taps are crap design.

  29. I think the general American need to look to to more developed countries for these normal everyday items, instead of inventing the deep dish all over.
    I love US don’t get me wrong, but…
    Thermostats, heating system, insulation, payments stems, door handles, house electricity, plumbing etc. You are 20-40 years behind.

  30. On-demand water heaters are common in Japan. They typically have a remote control, whose primary purpose is to automatically fill the bathtub with water at the desired temperature to the right level. For shower, the separately set temperature is held within one degree. Example: search bc-124v .

    Many such controls have an option to automatically vary the shower temperature in a random pattern from soothing to ‘wow’ cold. See ゆらぎのシャワー . It’s a very pleasant experience and I’ve tried to find such a unit for my home in the US. Unfortunately, whenever I search for “fluctuating temperature shower” or similar phrases, the only hits are sites assuming that this is a problem that needs to be fixed!

  31. Here in .au it’s not uncommon to run the tank into the mid-70s, then use a tempering valve to being the temps back down before the water enters the house.

    As for the article, this is why when we remodelled, we stuck with two proper taps. 270 degrees of rotation, multiplied by two taps equals very precise temperature and pressure control. Another nice feature is the only consumables are a washer worth about 20c… and we’re still on the originals after 3 years of use

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