FrederikNJS

That’s quite a wall of text…

Link for anyone interested in the video OP mentions: https://youtu.be/tz23G_UXCGA

There’s plenty of reasons for that to happen, but it depends a lot on how your heat source works.

Most regular furnaces will heat up the water quite high, and just leave it at that temperature, and as soon as the water temperature is about to drop, it starts heating again, therefore the temperature rarely changes, unless you have used up all the hot water (teenagers running long and hot showers for rather long, or just many people showering in short succession).

But many newer smart furnaces, and especially heatpumps will change the amount of hot water available depending on demand, and even dynamic electricity costs.

I have a modern heatpump which both controls the temperature and amount of hot water depending on usage patterns, as well at optimizing for heating up the water when the electricity is cheap. Just today electricity is 5x as expensive at 20:45 as it was at 15:00

This means that the hot water temperature and volume can change quite significantly, depending on the time of day and the electricity cost.

Right now I can see that my hot water is only 45.7°C/114.1°F, which fits well because no one in the house is usually showering at this time, and the hot water is only used for washing up and washing hands.

In the morning the hot water tank will likely be around 55-60°C/131-140°F, because that’s when people are usually showering, and the electricity is usually cheaper during the night hours.

Having a thermostatic mixer that can be set to a fixed temperature, regardless of the input hot water temperature is quite nice in this case.

The ones I’m talking about doesn’t just keep the pressure ratio static, they actually adapt to the temperature of the hot and cold water.

If the hot water drops in temperature, then the output water stays at the right temperature, but the output pressure might drop, as the mixer allow more of the hot water through, and less of the cold water.

Of course if the hot water drops below the set temperature, it can no longer maintain it’s temperature.

And yes these are also entirely mechanical, no electronics or even electricity.

Are you sure about that? I don’t see any numeric temperature settings. Every thermostatic mixer I have ever seen as at least a 38°C/100°F setting.

And also people are talking about the temperature creeping up during the shower due to the pipes heating up… That doesn’t happen on a thermostatic mixer.

But I guess limescale could seize it up… I have just never experienced that, and the water is very hard where I live…

Are thermostatic shower mixers not a thing where you guys live?