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 since (at least) the nineties.

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 become aware of the concept.

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.