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We have a shower that is being used multiple times throughout the day. For each use the target temperature is always ~30C. Unfortunately, the water in hot water pipe tends to cool down if someone was not using shower for longer time. If this happens, then the next person using the shower have to either:

  1. start at 100% hot water and 0% cold water. And drain the cooled down water from pipes. Only then ramp up intake of cold water. OR
  2. leave the shower to previous setting and drain/waste even more water because cold intake would be delivering water while the hot water temperature is still ramping up.

I was wondering if there is a valve, that I could preset to specific target temperature and it would automatically intake only hot water until the egress water temperature reaches the target temperature. Once target temperature reached, then it would start to mix the cold water so that the egress water temperature would not go over the preset temperature. How is such valve called in English?

Also, it may be a big problem for us if the temperature ever gets too hot. If such valve exists is it fool proof not to go over the target temperature?

The main goal here is to save water and reduce time that person has to wait in the shower for target temperature to be reached. While not mandatory, perhaps a digital screen with two buttons plus and minus to fine tune temperature would be a great plus too.

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4 Answers 4

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These shower controls seem to be common in the UK, I've never seen one in the USA. I'd be very happy to find one here. I expect importing one and connecting it would be a pain with the different pipe threads and sizes between there and here.

One knob sets temperature (thermostatically to a specific temperature, so you don't have to fiddle with it each time, but you can set it warmer or cooler to suit) the other sets the flow rate.

Thermostatic shower valve seems to be the right term, but not all results on that term are actually ones that work that way, so look to the details. There do seem to be (severely overpriced, IMHO) digital options out there, and now some in the US market at nosebleed pricing even for basic rotary control.

The OP should insulate the hot water pipe serving the shower as heavily as possible.

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    They are also known in Germany and Switzerland (we have them in our house in Germany and flat in Switzerland).
    – Martin Bonner supports Monica
    Sep 19, 2019 at 16:01
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These are also known as “thermostatic” valves and are used on showers, but also for hot taps in schools, hospitals etc to limit the hot water to a defined safe limit. This is usually around 46 degrees C.

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That's a tempering, (or temperature-control) valve, usually they are used to prevent scalding, but they could also be applied to pre-mix the shower water.

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I have yet to see a mechanical "smart" valve which allows 100% hot water and adjusts it for less hot water once the temperature is too high.

You would have to dive into digital solutions but I am not familiar with their internal mechanics: https://www.amazon.com/KOHLER-K-527-1CP-Digital-Interface-Polished/dp/B005ECLU2Q

You could have a recirculation pump installed to get "instant" hot water at the shower head.

https://www.homedepot.com/p/Watts-Hot-Water-Recirculating-System-with-Built-In-Timer-0955800/100426993

You could also choose to manually set the water heater to the "perfect" shower temp so that 100% hot water will always be the correct temperature. This of course assumes that the temperature is suitable for all non-shower uses.

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  • Is there a reason why mechanical valves can't use 100% of hot water before target temperature? Is it because they always partially open in certain temperature range?
    – user389238
    Sep 21, 2019 at 3:52
  • I am actually reading amazon reviews for some cheap non-digital mixing valves and some reviewers claim that it would drain 100% of hot water before target temperature is reached. Only then it starts to mix cold. amazon.com/gp/customer-reviews/R1K8UNNOKD95C9/…
    – user389238
    Sep 21, 2019 at 4:05
  • I had on 30 years ago that I salvaged from the x-ray film processing lab. You set the temp to what you wanted on a mechanical dial on the front. Kept it to better accuracy than the lab thermometer I had. Internally I think that the dial tensioned a spring on a bimetallic diaphragm.
    – Sherwood Botsford
    Sep 21, 2019 at 20:47
  • @HansSolo I have no experience with that product and we don't know if the reviewer has a recirculation pump installed which they failed to mention. It is listed as a thermostatic mixer so my assumption is that it is always mixing hot and cold water.
    – MonkeyZeus
    Sep 23, 2019 at 12:42

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