A manifesto on shower temperature control | Hacker News Reader

A manifesto on shower temperature control

benholmen.com

271 pointsaarondf171 comments

Much of the confusion in this thread comes down to the fact that in the US, the standard shower valve is a 'pressure-balanced' valve, which allows you to select a flow-ratio between hot and cold feeds, but does not in itself maintain any particular temperature - it just ensures that in the event of pressure changes on one or other feed, the overall mix is maintained (preventing temperature spikes if someone flushes a toilet).

Whereas in many other parts of the world, the standard shower valve is a 'thermostatic mixing valve', which allows you to select a temperature, and balances the inputs to achieve that desired temperature mark.

Note that if you go to, say, HomeDepot.com, and look at shower faucets, you will not find thermostatic mixing valves. Only pressure balanced. The only thermostatic component in conventional american shower valves is an anti-scald-cutoff. Thermostatic valves do exist, but they're not the ones that are bundled into showers and that therefore get employed by the average landlord who is grabbing the cheap standard parts off the shelf. Thermostatic is a premium option, and not one that even crops up in the search result filters for showers.

So most Americans have simply no idea that thermostatic valves are a thing.

Whereas if you go to, say, diy.com (which is the store of B&Q, an equivalent store in the UK), and look up showers, you will find all the basic 'mixer showers' have thermostatic valves.

I think a lot of the US fixtures don't even have compatible thermostatic valves. You'd have to get a complete replacement fixture, not just a valve/cartridge/insert.

You could define the desired characteristics in the shape of a curved hole within ceramic disks, such as the type commonly used shower faucets currently.

Yes, our thermostatic valve has around 270 degrees of travel on the temperature dial (which is separate from the water flow dial). Of those 270 degrees, it takes about 140 degrees to go from my preferred temperature to my wife's preferred temperature. With that large a range I can just turn it to roughly the right place before turning the water on and it's always just the right temperature. This isn't the cheapest valve (about £190) but I think many cheaper thermostatic valves are probably just as good.

Ours is one of these: https://www.amazon.co.uk/gp/product/B06XNZHZGJ/

Well, people may not know what they are and many are certainly expensive (>$80), but there are a lot of them at your local home center. Some are just "Heat Guard" (160/135F), but most of them are full mixers with the little expanding wax valves.

Here's a page full:

https://www.homedepot.com/b/Plumbing-Valves/Thermostatic/N-5...

As an aside, I just want any form of mixing tap for my sink in the UK, but apparently that’s still too much to ask for in many buildings here so I’m left with the separate hot/cold taps that are inevitably too far away to sort of “splash together.”

Go to IKEA. Buy mixer tap. Install mixer tap?

1. I’m not permitted to do so in my current housing situation (a temporary thing).

2. I would still occasionally need to use public toilets with separate taps.

I realise I phrased this as an issue with my specific sink, but I meant more broadly the situation in less-recently renovated buildings in the UK.

Mandatory Giphy: https://www.reddit.com/r/gifs/comments/5p9xfs/wash_yo_hands/

Also mandatory explanation why UK historically has had 2 taps: https://www.youtube.com/watch?v=HfHgUu_8KgA

Which in the end is understandable. It's outdated.

What isn't understandable is having the light switch OUTSIDE of the friggin' restroom.

Because that’s where there’s light to find the switch ;)

Seriously I’ve never had a problem with the switch being inside or outside as long as it’s by the door

Here's a scenario: you took a nice long hot bath. It got dark outside. You get out and want to turn on the light. Do you want to open the door and let the cold air in? Do you need to cover yourself first?

Crack the door open, reach through and flip the switch. It's only going to be momentarily cold and if covering is required a quick wrap of the towel will suffice.

I take your point though :)

None of the above; I use the pull cord switch to turn the light on

I've been in a multi-stall public bathroom where a person leaving turned off all the lights. For private bathrooms, I would much prefer to have the light control fully within my control while I am inside the bathroom.

In codes written before GFCI, making sure you can't electrocute yourself by accident could be achieved by:

a) establishing a minimum distance between the sources of water and electrical switches that would have to be measured, inspected carefully, be expensive to re-do, and possibly not be practical inside a small bathroom, or

b) requiring the switch to be outside the room

Some locales chose b, and never updated.

All bathrooms I've been in the UK have had a hanging cord for the pull light switch, this enables usage of the light inside the bathroom.

I've not seen a switch outside the bathroom since university.

> So most Americans have simply no idea that thermostatic valves are a thing.

Having very limited travel experience outside the US, my mental model of what the temperature control on showers was supposed to be doing was thermostatic, and I just assumed that they were just bad at it. You may have just explained one of my longest running minor peeves, which is that I've always found it basically impossible to maintain a shower temperature I find comfortable without needing to make adjustments. Given that I don't own my home at this time, I probably can't do anything about it any time soon, but at least from now on when I have to deal with the fluctuations in temperature I'll know that I'm not crazy and this is actually expected behavior.

It gets even worse when the water heating is flow activated (switching between 0 and 100%) and your faucet/shower head is too gunked up to allow for enough flow from at the desired hot/cold mix.

There's something on-brand about a software engineer seeing a problem, and spending a great deal of time fleshing out his solution to the problem, even asking manufacturers to reach out to him, yet missing the easily-findable fact that thermostatic valves are a thing. At the end he concedes that someone else must have already tried his idea but doesn't quite get to the idea that someone else probably found an even better solution.

I don't think you need temperature sensing to achieve what the author wants: you just need the amount of hot water mixed in to follow a specific non-linear curve. We just want to adjust sensitivity on an already-functional mechanism.

Given my understanding that water heaters are all calibrated for approximately 140°F, then even assuming some fudge factor it seems possible to do better with pressure-balanced valves than we have today. Especially if the valve could be calibrated at install time.

I have one of these grohe thermostatic valves. You can set the temperature and then use a push button to turn the shower on. The temperature is always set correctly as the on/off is separate from the temperature control. A majority of the range of the dial is usable. We still use cold water for cleaning the shower, or when you want a cold shower. During the shower, I have it set to hot, then slowly turn up the heat. This uses about half the dial's range.

The big difference is the grohe costs $500 while a standard builder grader valve might be $50.

https://www.build.com/product/summary/1391570?uid=3279009&jm...

<<How does a Grohe thermostatic valve work? The thermostatic valve mixes the hot and cold water to your pre-selected temperature and reacts instantly to any changes in the pressure or temperature of the water supply by re-adjusting the mix of hot and cold water.>>

I also have grohe thermostatic valve and enjoy it a lot! Worth every $ spent.

Same, nothing but good from my experience. Just a bit finicky to install like most European hardware and fixtures. Oh and their instructions are pictures only and hilariously obtuse.

Well, you can get Chinese thermostatic valve for few times cheaper.

You get what you pay for in my experience.

Hans Grohe panel shower broke, they don’t make panels like this anymore. Repair parts - $1600. Even BMW is not that greedy.

I replaced it with Chinese panel from Amazon for $500. Sure, not as fancy, but works just fine.

I have thermostatic valves here which costed me something like 80€.

It's not as fancy as the Grohe. It looks like a classic two knobs system except the right one controls temperature with gradation in degrees while the left one controls flow.

Better temperature control doesn't have to cost an arm.

I have a Gröhe thermostatic valve which came with the house. It's somehow broken such that you can't get the water as hot as advertised unless the dishwasher is running (?). And it's installed behind tile, so we can't just get a plumber to come in and replace it; we have to also line up someone to re-tile the shower immediately afterward.

We also have a pair of Gröhe sinks. We had to replace all four expensive, proprietary faucet hoses one-by-one as they ruptured. And then a couple more. It turns out they're short enough that it's hard to install them without kinking, and that eventually causes them to rupture.

I'm not a Gröhe fan.

(It also takes several minutes for the water to come to temperature in that particular shower, though it's only about 10 feet away from the water heater. I think the sink fixtures are affected too which suggests it's not all the shower valve's fault. It might be that we have pipes that are indirect and/or way too high-capacity, such that the total volume of water to drain between the water heater and the bathroom is excessive, and this is particularly obvious when using a low-flow shower-head.)

Sounds like an issue with your heater. Not sure why your dishwasher changes anything, they normally run off cold water and use their own heaters. Sounds more like you run your kitchen tap while filling the dishwasher, and flushes the cold water out of your pipes, and gives your heater enough time to get to temp.

Have you tried see if you can set the output temperature of your heater higher? Could be the output temp of the heater is very close to “shower” temperature, and a lot of heat is lost heating up pipes etc, something that could be sped up by increasing the heaters output temp, or improving the insulation on your hot water pipes.

The water's hot enough everywhere else (this bathroom's sinks after the aforementioned delay, other bathroom, kitchen). The heater's set to ~130 deg F, which iirc is the upper limit of what's recommended and considerably above the ideal shower temp.

It really seems to be the dishwasher running that makes the difference. I rarely use the shower in question, but my wife does every evening, and it apparently doesn't help if I've done all the rinsing/hand-washing and loading of the dishwasher but not actually hit start. I don't understand the mechanism, but I believe her. I'm not sure if the dishwasher draws from the hot or cold tap.

> Not sure why your dishwasher changes anything, they normally run off cold water and use their own heaters.

For North America at least, this is not true. Dishwashers are hooked up to the hot water supply[1] (and it's a good idea to run your sink tap hot to "prime" the hot water for the dishwasher).

They _also_ use built in heating elements to keep the water hot, and to dry the dishes, though.

[1]: LG Dishwasher Installation instructions (as an example), page 8: https://www.lg.com/us/support/products/documents/Dishwasher%...

All thermostatic valves have cartridges that eventually wear off and need to be replaced. Cartridge is accessible from outside by removing the handle held by the side screw (handle can be stuck and hard to remove) and then unscrewing the cap. Remove the cartridge, look at the part number and buy the replacements at Amazon. Obviously cut off water to the shower first.

Also handle has a small button on the bottom which blocks it from going into super-hot range. If you need hotter than normal water, press and hold this button while rotating the handle. (Handle is supposed to be calibrated when installed so digits on the dial match water temperature, but nobody does that)

I will check that out, thank you!

We did have a plumber look at this valve while here for something else, and he neglected to mention that...

There are cases where the cartridges are no longer available; that happened to us.

Some even have integrated shutoff valves, so you can replace the cartridge without shutting off the water anywhere else! What a marvelous world we live in.

Wow, I wish the last one I encountered had that. Plumber hooked up the shower valve fixture backward at my dad's new place. Also didn't even properly tighten the screws. Thermostatic valves aren't reversible, so it just didn't work right at all (basically got to choose full-hot or full-cold). They neglected to provide a shutoff for the shower, and he wasn't sure about draining whole system (it's an over-engineered water system with well-draw, sump pump, water softener, multiple redundant filters, gas water heater, array of in-floor heating, hydronic air furnace, and who knows what else). Access around/behind the fixture plate was non-existant.

In retrospect probably should have just clamped the soft lines upstream to effect the repair.

I have these as well, but they suffer the same underlying complaint that the majority of the dial area is for temperatures that are generally unwanted. As far as I can tell (and as the article records) there is a relatively small range of temperatures people want for showers or whatever, and then all hot and all cold.

So while with my setup I press a button and (sans hot water reaching the shower time) I always get the same temperature, dialing around to get that temperature is still fairly annoying.

As a friendly heads up to anyone exploring this space — temperature control is a complex dynamic between many components, chiefly the mixing valve, any local thermostatic dampers in the valve (rarer, but definitely a feature of high end mixers), and the source of hot water itself.

Mixer taps are not simply mixing hot water at temperature H and cold water at temperature C. The temperature H which your hot water source is capable of reaching is highly variable and certainly not constant. Higher flow for example reduces temperature as more cold water cools the heater. Heaters also cut out and oscillate as they overload.

Throughout the year the C temperature may also fluctuate by several degrees in a way that can trigger non linear effects in the hot water generator. (This is all assuming you have a just-in-time hot water source of course — more common in Europe than, say, NYC apartment blocks.)

Study the whole system and be prepared for unexpected non linearity everywhere. Heat loss per foot of pipe is a real thing, as is thermal damping of uninsulated tubing, to give two more examples.

If you can model the system then next up, you might try your hand at predicting the weather.

So we need like a capacitor for hot water at the shower head.

Or just active control? Set a desired output water temp, and let a computer constantly fiddle with the valves slightly to keep the output constant. Monitoring the current temp of the input lines would help but not be necessary.

I mostly don't like that every few minutes, I have to turn down the cold water a smidge, as fresher colder water from the ground comes up through the pipe. My shower has two valves for hot and cold separate, so I turn the hot water all the way on, then add just enough cold water to achieve human shower temps at full pressure.

Interestingly, control valves employed in this way tend to wear out very quickly or else they are slow and expensive so that they can be made more durable. Anybody working on this needs to hit that "good, fast and cheap" triple point.

This is why wax motors are commonly used as valve actuators since the only calibrations are the wax mixture, the mechanical force applicator, and the thermal resistance of various components in contact with each other

You don't need a computer, or even electricity. Thermostatic shower valves are 100% mechanical, and work beautifully. There are models available that will automatically compensate for both temperature and pressure changes, keeping the output temperature constant.

Alright, but can I run Doom on a thermostatic shower valve?

Let's run Half-Life 2

Like a showerstart tsv?

How about a 13 kWh 2.5 GPM tankless heater - https://www.homedepot.com/p/Rheem-Performance-13-kW-Self-Mod...

For 2.5 GPM (typical shower) it can do 35°F heating. If you have a low flow shower head (1.75 GPM), you can do about a 55 °F heating.

You could also do a water heater booster - https://www.rheem.com/innovations/innovation_residential/wat...

Another approach is to go to the other end where you've got the tank running higher than is safe to safely touch (e.g. scalding) put put thermostatic valves on all sinks and showers. This way you can run the water heater at 140° then then use more cold water to reduce it to the proper temperature which is a slightly easier problem than running your water heater at 120° and then cooling it down to 105° which gets to "mostly hot water with cold water for pressure". Running a tank at 140° also inhibits bacterial growth (e.g. legionella)

Not enough for a shower, but for a sink you could look at an under sink water heater ( https://www.homedepot.com/p/Bosch-2-5-Gal-Electric-Point-of-... ) - but you're looking at 6.8 GPH recovery time rather than a 2.5 GPM flow rate. The main advantage there is that you don't have move the hot water from the water heater in the basement all the way to a sink (lots of hot water in the pipe that then gets wasted) and thus less water use to get hot water to the sink and less hot water use overall.

An under the sink tankless looks like https://www.homedepot.com/p/Rheem-Performance-6-kW-1-0-GPM-P... with 0.5 GPM for a 65°F raise (you wouldn't even need to run hot water to that sink - this is what I do for my upstairs bathroom since the water heater is so far away that you need to run the water for a very long time to get the sink up to 'wash with hot water' levels).

All this additional complexity, while great for getting an engineer circle jerk going, is mostly irrelevant if you are using the dial for coarse adjustment and dialing it in by feel and if your shower is shorter than the time it takes to make your hot water supply change temp a meaningful amount.

Shower valves were literally two dumb valves for the first 100yr and they worked fine.

Absolutely.

I adjust my shower based on feel, sometimes I want hot, sometimes I want cold. Then I just turn then temperature knob.

I don't think I will ever want an explicitly 38°C shower.

You are overcomplicating this whole thing.

Just buy a thermostatic shower valve and have exact temperature control. They use a wax thermostat to precisely control the temperature.

Do not get the more common, and less expensive, temperature-pressure valve.

You can tell the difference because the bad kind has a single dial for both on-off and temperature control. It has no volume control.

The better one has one dial for temperature, and a second dial to turn the water on and control flow.

Mine is marked in degrees, and you just dial in the exact temperature you want, and leave it alone, and it will adjust as hotter water comes in.

Mine doesn't have degrees on it, but better than that, it can be adjusted such that the handle being in the neutral position (vertical in this case) is at whatever temperature you want. I set mine to 39°C which is what most people seem to enjoy. Turn it left gets you as cold as the cold supply. And then you can set a soft limit with a positive detente at some higher temp, which I have set to 42°C of course. So that you don't go overboard when turning right. And above that soft limit, you can also set the maximum temp, which I have set to 45°C. And the valve will shutoff if the temperature still manages to go above that.

This is also the case for electric showers though, where the shower itself contains the heating element and heats its own water, rather than taking arbitrary feeds of hot and cold water.

The shower doesn't need an internal heating element. All you need is an electric control system, which dynamically monitors the temperature coming out of the shower head and constantly adjusts the mix toward a set temperature.

I have a feeling these have existed for a long time in Japan.

It seems at least some of you could do with electric showers, since they have problems with showers needing time to heat up: https://news.ycombinator.com/item?id=34634223

You don't even need an electronic thermostat. You have manual thermostatic valves that do the same thing. I believe it has to do with the thermal properties and mechanical interface of a couple pieces of metal. As they expand or contract, it adjusts the mix to maintain the temperature set by the position of the handle.

I use a thermostatic mixer from Grohe (though there are more manufacturers in the recent years, including IKEA), and it handles normally both heating/cooling of the valve itself, and fluctuations of pressure in the pipes (when someone flushes the toilet).

Our hot water supply is off for 2 week per year for maintenance, and I use heater tank (which stores 30 L of hot water, enough to take a generous shower for 1 person). This way, cold water pressurizes both the cold valve, and the tank and the hot valve. I expected some random oscillations, but no, the thermostatic mixer worked just fine.

This is the one I have: https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2F...

I think the current ones are the way they are because the input temperature is not well controlled. I live in an old farmhouse where the cold water gets really cold in the winter and for years we've had a tankless water heater that has never worked that well but lately has gotten full of scales. We haven't tried descaling it because we're concerned that we'll kill it in the process of descaling it and won't try it unless we have a replacement lined up.

All of that means that the input temperatures are poorly controlled even when the heater is working.

The very large range of mixing ratios helps compensate for uncontrolled input temperatures. If the input temperature was better controlled (say with a thermostatic function) you might be able to calibrate the valves to a user-appropriate range, but barring that you'd need to put a thermostat right after the valve.

It's obviously your risk not mine, but I wouldn't be particularly concerned with descaling a tankless with vinegar causing a problem. I'd be more concerned with the uneven heat transfer causing damage (by overheating the metal that doesn't have adequate cooling from the water [that you're intending to heat]) than I would from the descaling causing damage (or more precisely, revealing existing damage).

You're supposed to descale them every year anyway

Or to put it another way: Spolsky said that users don't use 90% of the features in any app; unfortunately, they each don't use a different 90%. You don't use 90% of the shower faucet ratio range; unfortunately, each house doesn't use a different 90% of the ratio range...

Thing is, that 90% of the range is going to mean that you and I pick a different range from "hottest" to "coldest", right?

So it wouldn't be beyond the wit of man to fit a couple of setscrews, possibly accessible by popping the knob off, to set the "low" and "high" stops for the thermostat in the shower valve, right?

You'd think, eh...?

GNOME argument strikes again.

I don't use the acceleration and brake on my car all the time. I use the doors to enter or leave the car. I use the electric windows when i insert the parking ticket.

Another problem is the difference of pressure between the cold and hot water tubes. It's usually not to much, but I remember than in one hotel the difference was so big that if I opened both taps normally, I only got cold water. Moreover, the cold water entered into the hot water tube, so after closing the cold water tap I got only cold water coming from the faucet for a while. The solution was to open the hot water tap completely, and make a tiny turn in the cold water tap.

I have a kind of powerful dirt bike. People put “throttle cams” on them for this same reason. Usually you want small adjustments within the lower range of power. When you want the majority of power you usually want close to all of it.

Throttle cams are basically an off-center circle. At lower throttle you’re pulling a smaller circle and the throttle moves less. Then when the throttle is opened up you’re pulling a bigger circle.

Now I want one of those for my car!

If you car has an Eco or Power or Sport mode this is probably what it does. On my Toyota, Power mode makes the accelerator more sensitive and Eco mode makes it less sensitive (which is great for snow). Flooring it is the same, regardless of the mode.

You can't even rely on this, on my car the default behaviour is that the middle of the accelerator pedals range of motion is the "sweet spot", and in fact flooring it will trigger the hill climb assist and cause the automatic transmission to go down a gear.

Typically there is extra resistance at the downshift position, and you already have full throttle in the current gear before engaging it.

I haven't owned a car with them, but I thought those modes were to control when the gear shifts happen. Sport will optimize acceleration while eco will change up sooner to save fuel

I hope Sport mode changes both rpm limit and pedal response.

My car has them, but it is a hybrid with planetary gear, so would not make sense for it.

Haha, probably we want a hinge on the joint between the gas pedal and the curved pin thing it pushes down? And move the pedal back or forward? Or yeah, I love to be super ignorant of the classical Simple Machines and try to work out mechanics like this.

I’ve actually had some success with guess-prototyping mechanical contraptions in the physics-sandbox game Besiege: https://www.spiderlinggames.com/

I can also emphatically recommend just getting a Husaberg 550, 570, or 650 %D

These days you muck with the pedal position to throttle mapping, no need to change the mechanism itself.

If your car has electronic throttle the engineers (with tons of input from the fuel economy people) have already decided for you.

If it doesn't then the linkage is already designed to be non-linear by adjusting the arc of the pedal linkage vs the throttle linkage.

These exist for most modern cars, you can buy a plug in box that remaps the throttle curve.

These devices exist. You just don't want to pay for them.

https://www.kohler.com/en/products/showers/shop-shower-trims...

What you have in your shower is a cheaper anti-scald valve that just prevents super huge spikes in water temperature when the input pressure changes (i.e. your wife flushes the toilet).

Like PaulHoule says, you need monitoring of input and output temps to do that. And that's technically possible, but it's complex and expensive.

Huh? Regular thermostatic valves do not provide perfect regulation but they do in fact provide a fairly stable output temperature regardless of cold and hot water temperature, by entirely mechanical means. I have a cheap IKEA shower control and output temp is stable for the full duration of my shower even though cold nor hot water supply is stable due to a shower drain heat recovery unit.

The article is mainly about wanting the regulation to be between 35-45C instead of 15-55C.

you can change the top end by lowering the temperature of your hot water heater. We have ours set at 120. Using a lower hot water temperature is a way to give you a wider range of useful temperatures.

In texas during the summer we often take showers with no hot water (or very little hot water).

This isn't always feasible depending on the location, age, and type of water heater, and how many things with different temperature needs are connected to the same water heater.

A tankless water heater with a feeder pump, dedicated to bathroom use and with a bathroom-installed remote control, makes this trivial. It's probably also more efficient, easier to use, and (vs. thermostatic valves) about as easy and maybe also cheaper to implement than any fussing with valves.

A 30-year-old tank heater in a basement that needs a wrench to adjust a temperature that won't meaningfully change in a 2nd-floor bathroom for another half-hour, and also has to serve a dishwasher and clothes washer that might also run at higher temperatures at the same time, can't swing this as easily, or at all.

> you can change the top end by lowering the temperature of your hot water heater. We have ours set at 120

I’m not sure that’s a good idea. 120F is in the danger zone for Legionnaires' disease. https://en.wikipedia.org/wiki/Legionnaires%27_disease#Preven...:

“Keep water temperature either above or below the 20–50 °C (68–122 °F) range in which the Legionella bacterium thrives.”

Interesting. On the other hand, when bringing a newborn home from the hospital, the take-home literature instructs new parents to turn the water heater down to 120 F to prevent risk of scalding.

I wouldn't worry about it. Almost every modern boiler will bump up the temperature to 60C / 140F once a week to prevent Legionnaire's, may even be a mandatory feature depending on where you live.

The "right" way to do this is a thermostatic mixing valve at the water heater output. This lets you keep the tank at 150°F (or whatever) but the output gets mixed down to 120°F (or whatever). It also gives you an effectively-larger tank which can be very useful in certain cases.

Of course, you might say, why not put the thermostatic mixing valve at or in the shower, which also works pretty well!

> the 20–50 °C (68–122 °F) range

That's clearly a case of conversion results being given unwarranted precision.

Are cheap thermostatic shower mixer controls not so common outside middle-of-europe?

This is the one with one grip that lets you set the temperature, and the other sets the flow rate.

It'll (try to) hold the output temperature steady even if the input temperature varies a bit.

In my experience (US), they seem to be uncommon in residential properties. I've seen them in many hotels, though.

Indeed this solution has been standard in much of Europe for decades.

It seems to have had slower uptake in the US. Donald Norman’s ”The Design of Everyday Things”, 2013 edition, contains this passage in a list of different faucet designs (p. 151):

> Control temperature and rate of flow. Use two separate controls, one for water temperature, the other for flow rate. (I have never encountered this solution.)

I e-mailed Don about it a few years ago, and by then he had encountered it.

I guess this Don person never traveled outside North America.

We have the same thing in Japan; they look almost identical to the controls I've seen in Germany. I just leave the temperature control set to the same position, and turn the other side to get the flow rate I want. It's amazing that Americans don't even know these things exist, and are still using ancient pressure controls instead.

I feel like a mechanical version could be made which has a separate gear ratio for the middle of the operating spectrum.

Alternatively, for the traditional "hot/cold knobs" function, I don't see why a third pressure knob couldn't be added.

I could leave the hot and cold knobs turned exactly where I want them to be, with some arbitrary number dial helping for consistency, and I only have to turn the pressure knob to let the water start running.

I shouldn't have to spend $1500 for that.

its not really gears? I assume its some kind of bi-metal strip. if so, you would just need to change the shape of a cam (?)

A cheap valve between the hot/cold valves and the bath faucet or showerhead can provide that.

Unfortunately, single-handle mixer valves aren't usually designed to have their output blocked under pessure like that. So that's when it starts getting expensive and specialized. But with traditional separate hot/cold valves, it works fine.

I feel like this could become the next Swiss watch. Bring joy back to showering. Meticulously hand crafted by artisans in the Swiss Alps. Features include:

- Polished stainless steel case

- Intricately geared shower control valve with see through cover

- High precision temperature set point control

- Compensates for input water pressure / flow to maintain temperature

- Comes with unique ID and certificate of authenticity

Obviously it will require annual servicing to make sure ensure continued operation. Your smugness will keep you warm long after your hot water runs out.

> † The author acknowledges the recent trend of "cold showers" and considers them (a) a trend, (b) undignified, (c) a waste of some life-sustaining solidary time.

Hear, hear!

I actually find cold showers in the middle of the day quite life improving during the summer months.

I always end my showers with cool water because it works wonders for preventing dryness and itchiness on my skin. I use actually cold water to rinse my scalp.

This is all very different than a shower with no hot water mixed in whatsoever. Deepening on the climate and season, water that cold can cause physical harm. In other words, I'm betting most of these "cold showerers" are actually use cool water, not anything as dramatically cold as they might want us to infer.

On a FIRST robot, we needed something similar. There's "full reverse", "full forward" and "I need fine control", and the original mapping of joystick to wheel motors was linear. It didn't work well for "fine control". We ended up with motor = joystick³ (or some other odd, greater than 1 power; it might have been ⁵). Then you fix, via coefficients, the endpoints of the equation such that the lowest joystick value hits the full-reverse motor setting, and vice versa for forward. The exponent dampens the curve near zero, so there's more "joystick space" spent on the very slow speeds for the fine control, but the operator can still ask for max speed if they want it.

(With joysticks, you also have to deadzone the middle, as "operator has centered the joystick" will sometimes report joystick values of 1 or -1, instead of 0. Or buy a better joystick.)

I'm not 100% sure I'd apply this to a shower: max hot on my shower is hot, I don't usually ever want it. And I wouldn't want to scald someone.

For a long while, our shower was not the typical tiny goldilocks zone surrounded by ice and lava: … it never really got above "lukewarm", even at max. We had the shower valve replaced and it works better now. (And, apparently, as I learned, there's a mixing valve at the hot water heater: i.e., the hot to the shower is not direct from the water heater, like I had imagined. We raised the temp there, slightly.)

When my wife and I met she lived in an apartment with an amazing shower. The pressure was good but the temperature was fantastic. I had never had an apartment shower with water that got so hot. I barely even went half-way on the knob before I was turning it down. I asked about it and her response was "oh yeah I complained to my dad and he looked at the heater, there was something on it that he broke off." Turns out there was some piece of plastic or something put on by the landlord to limit the top temperature of the water, so he took it off.

It didn't keep the hot water from running out but when you had it, it was great.

>(And, apparently, as I learned, there's a mixing valve at the hot water heater: i.e., the hot to the shower is not direct from the water heater, like I had imagined. We raised the temp there, slightly.)

When we changed from instant hot water to water tank + heat pump, the guy said the tempering valve was a safety thing (IIRC ours was set to 60 degrees Celsius by default, but could go up or down about 10 degree either way). That is, if you accidentally step in the shower with only hot water on you'll still hurt yourself but the damage will be limited to "strong profanity and aloe vera" instead of "you've won a stay in the burn ward".

Although saying this, I did a quick bit of research and found that 60 may still be too high [1]. I have an IR thermometer so I think I'll measure the temperature of my shower (after any loss from pipes etc.) and see if the tempering valve needs adjusting down.

[1] mild nsfw - image of scalded foot https://whywait.com.au/a-serious-hot-water-burn-occurs-in-on...

"Safety" is also what my guy said. The problem is that in isolation the answer doesn't make any sense: why should I be heating water up to then re-mix cold water? Is that not a waste of energy?

The fuller answer, I think, is that the "raw" hot line additionally goes towards uses that can take scalding water, one or more of the dishwasher and the laundry, depending on whether you have either or both of those in your dwelling. (I hadn't thought of those, since my concern was on the shower. I also can't see the piping, in my place, so it was a black box of sorts.) For uses that might interact with a human, then it's a safety thing, then it makes sense to do the mix with cold. (I believe the other line, the shower bound one, is called the "tempered hot" line.)

My guy also refused to raise it too much, or disable it altogether, citing codes and that it couldn't exceed like 140℉ or so. Which was fine, really, since I was asking for it to exceed 95℉…

Storing the water at a higher temperature effectively increases the capacity of the tank. Also the stored hot water has to be above a certain level (~60 degrees) at least some of the time otherwise it won't prevent any bugs growing in it.

Yep... particularly Legionella Pneumophila and friends which can cause Legionnaire's disease.

I was taught as a child NEVER to use a hot shower from a water tank or drink warm water from the tap after a sustained power outage until the tank has had time to come back up to it's normal temperature... Legionnaire's can straight-up kill you via pneumonia.

I always wondered if Britain turned out more than its fair share of safecrackers because of our traditionally crappy shower controls and how a sixteenth of a turn meant the difference of maybe 30 degrees of heat.

Gosh, Britain doesn't have two shower heads per shower (one hot, one cold), does it? I know they do that for taps.

No, we don't

There are some older showers in Ireland, so I guess in the UK too, where you basically use hot/cold water taps and pull a lever which redirects the mixed tap output to a shower rather than the bath. Mostly replaced by electric showers these days though.

I'm obsessed with showers and also wonder why we are so spectacularly bad at making consistently good showerheads with consistently good pressure and temperature control.

One issue the author overlooks is that we have minimal control over the temperature of the cold water, and this temperature fluctuates throughout the year (at least here in NY, not so much where I lived in SF). As a result, the range of the dial I use changes from summer to winter. There are hot parts of the dial I use everyday in the winter that would simply burn me if I used them in the summer.

Temperature can even change during the course of the shower! I notice this mostly in the winter. I speculate this is due to the cold water in my building pipes being used up and then replaced by the truly cold water from underground. I once tried to shower with that icy water when the hot water went out (just before a big trip) and I managed to completely numb my lower body (I did not have the fortitude to try and shower my upper body too).

The water pipes to my shower go through an exterior west-facing wall. Mornings in the winter, the first half-gallon or so of water is basically the same temperature as the outside air-temperature. Evenings in summer, the first half-gallon can be painfully hot, even from the cold-water supply.

We have central hot water, and in winter hot water is incredibly hot, because the thermo-power station runs high.

Ah yes, showers that have frigid, cold, and scalding settings, and not much in the way of warm.

This is is usually because the hot supply is under relatively less pressure, going through a tank and more pipes. So, nice and warm means hot is almost fully open and cold almost fully closed, to get an equal mix of both. Very little room to work with.

The right flow restrictor on the cold supply will make midway an even mix, and so more of the dial is useful. Very much worth the $10 the next time you have access to the plumbing.

In a correctly plumbed system there should not be a significant pressure differential on the hot and cold sides. When done correctly (upsized feed from the utility) with balanced loops or a manifold flushing the toilet shouldn't effect shower pressure or temperature at all.

I can testify to that because in our house it works that way. The only time a shower is affected is when filling the large bathtub - which fills much faster than in most homes because it has a very large feed but that's the tradeoff since there isn't enough volume from the utility in that one case. Otherwise people can flush toilets, use the kitchen sink, wash clothes, etc and showers are not affected whatsoever.

Another factor is insulation - even many modern homes don't insulate the hot water pipes so even with an instant hot water heater that responds quickly you still have to pay the lost heat cost of warming the pipes and everything the pipes touch before the temperature fully stabilizes. This is a cost-saving measure - there is no reason the pipes couldn't be insulated. If you throw in a recirc pump then you can have instant hot water at every tap with very low energy cost.

Even if the pressure does not change, the temperature definitely does. Currently, cold water is basically icecubes blasting out the shower head. Warm/hot water, on the other hand, is sometimes affected by a heat exchanger (district heating) malfunction.

2 side-rants:

* Physical shower controls themselves. The typical US single-handle shower control is awful. Maybe I'm stupid, but it's never intuitive to me which side is hot and which side is cold. Much of the time the handle is pointing down, so you have to visualize an arrow extending through the top of the control, pointing left (hot) when the handle is on the bottom right. Sometimes they point entirely different directions, or the rotational positions of off, cold, hot make no sense at all. As I write this, it occurs to me that it's probably obvious that cold is always closest to "off", and "full on" is always full hot, but I'm over 40 and this has never occurred to me until now, so it can't be just me. Anyway, for whatever reason, when they're not labeled, i've never been able to 'remember' which side is hot and which side is cold. Again, maybe it's just me, but I've never had any other such dyslexic tendencies outside of faucet control. I think in my head "C" is on the left because it places C and H in alphabetical order?

* Tankless hot water heaters. I want to like them. I've had them in my last 2 houses, covering the past 12 years. I can't imagine buying a water heater with a tank, but... The (central) tankless heaters take 15 seconds to turn on, and the water takes forever to make its way across my tiny house. So much water and time is wasted. And they shut off after some minimum flow rate. So if you try to use 'too little' hot mix (hot water heater set 'too high' or cold water input too warm, say, in the summer), the water heater decides to click off.. which you only notice 20 seconds later as the hot water trickles out of the pipes, and now you have to wash, rinse, repeat the whole awful cycle of turning the handle to full hot, waiting for hot water again, turning it down, but hoping you didn't turn it down too far. I've turned the hot water heater down as low as it'll go without much noticeable difference in this behavior in either house. Perhaps because the minimum flow rate actually depends on the setpoint of the hot water, which would make sense. It's worse in the summer. It's only a problem I have in 10% of my showers, but it drives me nuts.

I've focused on this problem for some time too.

The ultimate solution was to buy a color changing shower head from LIDL. This made it so easy to always be in the right temperature zone when taking a shower.

The shower head has lighting that turns to green when the temperature is between 34-38C°. It's red when the temperature is above 38°, and turns to blue when it's below 34°C.

It also shows the current temperature as a display which you can see while you are under the shower. The sensor setup also seems to be powered by the stream that flows through the shower head and only turns on when water is running.

I hope this helps.

Reminds me of the time I went to England, ended up in a cheaper hotel with a wash basin that had two taps on each side, hot and cold.

Although it was a real pain, what really shocked me was the carpet floor in the shower room...

But comfort areas are hugely different.. I prefer the range from scolding hot to ice-cold (I start my shower in the middle area, then prefer to turn up gradually as I get used to it until it's very hot (so hot I'd feel uncomfortable if I started at this temperature), then after a while I get very warmed through, and I turn straight to the coldest setting and enjoy the constrast from burning hot to burning cold, and that's the perfect finish for my shower. Then I step out of the ice cold shower and enjoy the warm air against my skin (even if that warm air is about 19.5C at the moment, it still feels warm in contrast to the ~2C water)

Why not simply have two separate valves for hot and cold? It's a one time expenditure!

But of course this foolishness has competition: no bidets anywhere!

Not on the screen, is that pipes are a non linear heat regulation plant. https://en.wikipedia.org/wiki/Plant_(control_theory)

Means, demand for warmth is not fullfilled, until the heat has warmed up the pipes, and then its over fullfilled, to the point you regulate towards. Same goes towards the other direction. Cold first cools down the pipe before becoming fully cold..

Thermostatic shower mixer by Grohe and some more manufacturers fixes this problem, and also 1) when someone shuffles the toilet on the same pipe, 2) when you use hot water from a heating tank on the cold pipe.

https://duckduckgo.com/?t=ffab&q=grohe+thermostatic+shower&i...

Yikes, the max temp is 140F. That’s dangerous and has been a code violation for a long time, for good reason:

https://www.pmengineer.com/articles/94780-upc-continues-to-e...

This would depend on the temperature of your hot water feed, which is likely much lower.

It’s like having a speedometer in your car that goes to 180 mph.

Also we have body sensors which detect acute over-temperature situations and cause us to remediate the situation before damage can occur. Usually while screaming something profane.

In case you have never been in a slippery shower or encountered anyone with one of many possible disabilities, excessively hot shower water is a genuine hazard. For example:

Slow reaction time (you can get burned very quickly by excessively hot shower water)

Limited sensation in some part of one’s body

Balance issues or movement issues.

Anything preventing one from getting to the control or out of the water very very quickly.

A shower delivering 134F water is hazardous and serves no purpose.

Who goes into an unknown shower and doesn't start out with the control at the cold end, slowly increasing it until the water is hot enough? That's like getting into a car you've never driven before and giving it full throttle right away.

A shower delivering 134F water is hazardous and serves no purpose.

It does if you want to clean something other than your body in it.

I was off by 6 degrees (looked lazily at axis labels, not at the actual data). But the OP actually measured the temperature. It says, right in the article:

> The minimum temperature was 44.4°F (6.9°C) and the maximum temperature was 134.1°F (56.7°C).

So yes, this shower violates the code.

> So yes, this shower violates the code.

Again, the shower is not the only one dictating how hot the water can get, the water heater does as well. Turning down the temperature on the water heater will make the max temperature of the shower also go down, vice-versa if you put up the temperature in the water heater.

Could be that they just run their water heater really warm, some people seem to do.

You can't turn down the water heater by much, the temperature is usually kept at around 60C/140F to prevent bacterial growth.

It also depends on the temperature of the cold water being mixed in.

It really shouldn’t be, at least for homes where the owner gets to choose.

Being able to set you water temp extremely hot makes your hot water last longer because the comfortable water temperature is say like 70% cold, same applies for laundry.

Also consumer dishwashers perform much much better with higher hot water temp.

That’s solved by European dishwashers. They take in cold water and heat it up themselves.

If you have any recs I can buy in the US I'm all ears. Because mine "heats up" but not enough to make an actual difference between turning up the tank heat.

There is nothing wrong with setting one’s water heater tank very hot (except potential inefficiencies — there would be more loss when not using hot water, and heat pump water heater can be less efficient heating to a higher temperature). Codes allow this.

What codes do not allow is excessively hot water coming out the fixture. IMO this is the most sensible kind of code: it disallows a specific unsafe outcome. You are not allowed to build a house that burns unsuspecting users of the sink of shower.

So you can apply technology! There are thermostatic mixing valves that can be installed near your tank to serve your whole house or at the individual fixtures. They’re not free, but they’re not terribly expensive, especially if just one is used for the whole house:

https://www.supplyhouse.com/sh/control/search/~SEARCH_STRING...

That's what I thought too. Why not take the first step to reduce the temperature setting on the water heater?

Yep, my first thought was why nothing was done at the water heater level if the full-hot is way too hot.

> "it seems very reasonable to design a shower valve that is biased for human temperature preference"

It's not that simple. Hot water temperature varies greatly from one home to another. Cold water temperature varies tremendously from summer to winter. Take a picture of your shower control for the same water temperature in winter or in summer. You will see it's not turned at the same angle, because in winter you need a lot more hot water to balance the ice cold water from outside (especially if you live in the country, it will be ice cold, trust me). As a consequence, the part of your shower control that you call "confort zone" can be almost 100% too hot or 100% too cold in another home or in another season.

I've noticed you don't see the pivot type valves anymore where you can just go up and over to hot right away. Most shower valves now are turn-throughs, where you start at cold and go up to hot. Having installed a few now, I think this has to do with the federal law for having a scald prevention device in the valves control (much like having a low-flo device in shower heads.) Both instances, they are plastic and so you can remove them or adjust them later. I think it's just easier to make a scald prevention device for a turn-through valve than a pivot valve and that's why most shower handles suck today. It's just a tiny plastic piece that impedes how far into the hot range the handle will go.

I've been enjoying my digitally controlled shower temperature for years now. Japan figured this out a long time ago. I know the the temperature I like for a given season, and have up/down buttons to adjust it if needed.

Just bought a Grohe thermostatic shower control and it’s one of the best things I’ve ever bought. Saves water and keeps the temperature comfortable. Highly recommend a thermostatic control.

I saw these in Germany and bought one for my home when I got fed up of adjusting the shower at home. I told my parents, -- they'd have the same problem, and one would shuffle the toilet while the other was taking shower -- but they didn't bother, until I just bought and installed one for them as a gift.

I'm actually installing a thermostatic valve today to go with a recirculating pump I have setup on an electric heat pump water heater. I'm going to be installing it exactly like this guy with an expansion tank. Does anyone see a problem with this layout? Apparently, his doesn't work.

https://www.amazon.com/review/R3NQCKZCEQLLLC/ref=cm_cr_srp_d...

Get this and install by the heater: https://smile.amazon.com/dp/B08R1HKZ78/ or this: https://smile.amazon.com/gp/product/B09V7MDZHF under the sink.

There's a remote available also. By sure and carefully read the details - there is an "E" model, be sure and understand the difference and pick the right kind for your setup.

I have everything I need, I just need the position of the expansion tank confirmed.

I'm kind of confused on the question since you said "expansion tank". Which I guess is used because of a check valve - but that's if you put a check valve to the cold water back to the city, which isn't really part of a recirculation installation. A check valve for the recirculation should not need an expansion tank.

A heat pump water heater will not work well with this mixing valve - just pipe the hot water direct to where it's needed, don't mix it with cold. A heat pump doesn't really want to make very very hot water, unlike fuel heat. This valve is meant for you to heat the water extra extra hot, then mix it. It's used when you have a small tank, and a lot of usage. It wastes energy, but gives you more hot water.

It's just a bad idea to mix with a heat pump which much prefers lower water temperature.

And using this mixing valve with a recirculating pump can't possibly work. This valve adds cold water, but a recirculating valve circulates the same volume of water, and does not add any. There's simply no way that it can work - it's impossible. Do you get why?

Are you planning on having the recirculating pump always on, or do you prefer to press a button and wait a short time for the hot water? I ask because if you prefer the first type, you really want a dedicated return pipe for it. The second type can use the existing cold water pipe for return, but even then works much better with a dedicated return.

Without a dedicated return line you never have cold water, the cold water is always warm because when you turn on the cold water, some hot water flows via the pump, and to your faucet.

The expansion tank should be connected directly to the hot output of the heater before any mixing valves or recirculating stuff.

Why is there no mention of the water heater temp control? If the water is way too hot on one end, you need to calibrate your input before worrying about the control of the output.

Our shower has two dials: temperature and pressure. The temperature dial has a specific temperature that it will "snap" to. (When increasing temperature, it will stop there unless you hold in a button. It doesn't snap when decreasing the temperature.) Generally, I find the temperature it snaps to quite pleasant, so I just put it at the snap temperature and then open for the water with the other dial.

Concerning " Why are we wasting so much potential control area on water temperatures that no one wants? ", I am a professional plumber, have been for decades and... on one occasion I was told by an aging resident of a new-build home that there " wasn't ENOUGH control area" on her brand new Moen tub/shower faucet! WOW.

The US insists on using mixet valves wherever possible, while most other countries give you hot and cold knobs which you can adjust to taste.

Don't think this is a US-only thing, seems to vary even inside countries. Been to a lot of countries, and most showers have been without single knobs for hot/cold, but seen that too of course.

Very interesting exploration. However does this assumption really hold for the commonly used valves: >Since temperature has a nearly >linear relationship with control >rotation

I thought the valves have circular openings and the flow changes non linearly, which I have always experienced too.

Just a few days back I was thinking of why no one has thought about linear controls.

The amount of water wasted waiting for the water to warm up must be astronomical. In my place it can take three or four minutes of the water running to get warm - if not longer - and I don't think that's atypical.

Multiply this by 7 days a week by everyone who showers in California alone and it seems like an issue that should get some serious attention.

It's particularly bad with my tankless hot water heater that apparently doesn't even turn on for 15 seconds, and then you wait for the hot water to get to the shower. I swear the whole thing takes 60-90 seconds, and I live in a tiny house. I can't fathom what the hot water is doing on its way to the faucet. (well, yeah, some of that time is also spent heating the cold uninsulated under-house pipes).

I swear I had to wait nearly 5 minutes every morning before _warm_ water starts coming out, and our tankless heater was a wall away from shower.

People should stop buying pressure-balance shower valves, and switch to thermostatic valves. My shower valve is actually marked in degrees on the dial, and you set it to exactly the temperature you want and then don't mess with it - it will adjust as hotter water arrives.

There is a special kind of engineering that goes into luxury cars to get the windows to make a pleasing sound when you roll them up. That's the kind of engineering it takes to make a shower that only produces comfortable temperature water.

This is a result of the valve construction - you have a cold water pipe and a hot water pipe coming in, and the knob/lever is connected directly to a single valve that controls volumetrically how much the flows mix. This arrangement is both cheap to manufacture and easy to install and repair.

Adding proportional control isn't too hard. Certainly an easy option would be actuating the valve electronically and just using an encoder in the knob to control it digitally. There are a lot of advantages to this, such as being able to automatically comp for actual water temperatures and customizing settings for personal preference, but it's understandable that people might feel uneasy about a cheap electronic device in close proximity to the water they are in. I'd point out that this hasn't stopped us from putting things like lights in our showers which by necessity draw much more power, but some may still be concerned. More likely it is the lack of experience with electronics that valve manufacturers and plumbers have that make them hesitant to change.

For a mechanical solution, you could transmit the torque via a gearbox instead of a direct shaft. Switch gears to get higher or lower resolution control. You can even have a single set of gears with variable diameter sections to have higher precision in a fixed subsection of the range. Unfortunately this would not allow for easy adjustment for an individual installation, nonetheless different people using the same shower. The increase in manufacturing cost and installation complexity would probably not be huge, but in such a high competition commodity market it would be noticeable.

But solving the real issue, a lack of fine control in the important range, is actually much easier to solve. Just make the handle on the knob longer/larger diameter. Especially if you just want to modify an existing installation, attaching an 18 inch handle onto the existing knob is something just about anyone could do in a few minutes. For precise control, grip it on the outside, for fast large changes, choke up on it. For the OEM, a design with a long handle is pennies more expensive to produce at scale, easily justified for even a very small competitive advantage. Maybe some people really like the aesthetics of a small handle, but I've never once heard someone complain a shower handle was too big. I still think the electronic controller option is better, as you can deal with other shower temperature control problems like the long heat up times of the pipes and the variable ideal water temperature at different points in the shower, but the perfect can be the enemy of the good enough. Frankly it's just weird that I can't seem to find a shower handle longer than about 6 inches available for sale right now in a quick google search.

I prefer cold showers, and have the opposite complaint. Most valves are over-optimized for 'normal' shower temp ranges, and still mix in a lot of hot water even on the coldest setting, which makes taking a really cold shower impossible.

Thinking from first principes, what about a shower handle that copies how air conditioners and heating work, something like a screen showing the exact temperature of the water with an Up and Down buttons to control the temperature.

These exist: https://www.build.com/digital-showers/c131744?facets=applica...

I loved the seriousness of this manifesto. A most-pressing issue indeed. The search for the better shower handle will be squabbled just like the quest for a better mousetrap.

My two cents—a cam in the shower handle could follow that curve.

This is one of many problems with the lack of innovation in the home in the last 40 years. Being a former IOT UXE I've been fascinated with this space. It's too bad my pitches never took off.

There's no lack of innovation in the home. It's just that Americans refuse to adopt any of the innovations that have become commonplace in the last 40 years.

I was house-sitting one time and took several miserable showers before realizing that the temperature dial started out on hot and got colder the farther I turned it!

Why does my kettle have a thermometer but my shower does not?

Because you (or your landlord) bought one without it - showers with thermometers do exist.

Moreover, showers with purely mechanical thermostats exist.

Because your kettle is electrically heated but your shower mixes hot and cold mechanically.

That said, you can pay $$$ for an electrically controlled shower with a thermostat. And also worry about the electronics and motor breaking at some point.

Because you're American.

In other countries, showers have temperature settings on the controls.

Just add a gear affixed to the handle, and then a second gear mated with that, and find the gearing ratio that allows the granular/sensitive inputs you want.

Quick and dirty solution: find the optimal position for the valve(s), mark where they are relative to their base, and open the valves to that position each time

My cold water temperature fluctuates with the outdoor air temperature, doesn't everyone's?

I want a valve that turns off the hot water supply completely after 10 minutes

I want to be able to control flow and temperature separately.

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