In some parts of the world (such as England) it is compulsory to fit a thermostatic valve to a new shower or bath. This is apparently for safety reasons, to prevent scalding.
My problem with thermostatic valves is that they try to maintain a constant temperature. As the hot water depletes, it adjusts the mixing ratio. But this means that the hot water depleting creeps up on you stealthily and then all of a sudden, you have no hot water and no warning. I much prefer managing the mixing ratio myself so that I know when I do not have time to wash my hair or something.
So I wonder, is there a product that permits a maximum temperature but does not try to maintain a constant temperature? This would satisfy the safety requirements and would allow me to know when hot water is starting to run out.
I’m not sure if you are aware, but this is the normal behavior even when you have no mixing valve. Tank water does not mix very much: you draw hot water from the tank then the hot water runs out.
Because the cold water is drawn in over the heater element / gas element, if comes in warm, but when it’s warm, it’s not being mixed by the mixing valve.
Using a mixing valve allows you to set the tank temperature very hot, which allows you to use a smaller tank. Using the different mixing valve you request is unlikely to help you.
When I was growing up, the shower would slowly start to get cold at some point. This was in South Africa. At my house in England, it gets cold more suddenly.
For the avoidance of doubt, a thermostatic valve is different concept to a mixing valve, although in practice mixing valves are almost always thermostatic.
As above. There isn’t really a mixing valve that will stop the sudden drop in temperature. The water doesn’t slowly drop in temperature from the HSW. It just abruptly goes cold. The valve has as little warning of this as you do. This can vary a little depending upon the history of water drawn off and heating time, but heaters are designed to stratify the water as much as they can and avoid mixing.
A valve that tried to maintain temperature would just shut the water off when the hot ran out. They generally don’t do that, but rather open the hot side of the valve fully, and close the cold. (I doubt they fully close either side, but maybe some do.) The clue this is starting to happen is usually that the pressure drops. But much depends upon whether there is a gravity fed HWS or mains pressure. Mains fed and it is more subtle, but noticeable.
One way of managing things is to use a large storage HWS and set it to a much lower temperature. When I was a child my parent’s house had a large storage HWS and the temperature was set to be perfect for a shower. We just turned on the hot tap, and never needed the cold. One win is that this tactic saves heating costs, as the temperature delta is less, so the HWS and pipework lose much less energy to the environment. Of course when your sister grows to be a teenager and starts to take very long showers, nothing avoids arguments. But it is no different to a smaller storage system set to a hotter temperature.
The other tactic is instant gas heating. That can be fabulous, but not for everyone, for a whole raft of reasons.
My current house has a regulating thermostatic valve on the main bathroom shower. It works great. However, putting a couple of loads of washing though on hot setting can still result in a chilly shower later. YMMV
It sounds like I had an unconventionally designed water heater when growing up, and what I am really looking for, instead of a special valve, is a water heater that mixes in the cold water a bit
When we were kids a long time ago the designs weren’t as good at segregating heated water from incoming cool/cold water.
As such, and given only dumb valves, you could set your temp, take a shower until the water temp began to noticeably decline. At that moment if you quit screwing around and rinsed off quickly in the distinctly cooling water you could get out in a couple minutes, getting the very last of the warm-enough water, and be sure you got every drop of hot steamy goodness there was to be had. Sux to be anyone else in your household for about an hour though.
Modern HWHs make that transition take 30 seconds not 4+ minutes. Then thermostatic valves of whatever nature mask that 30 seconds warning down to just a couple seconds. Surprise!
Sometimes progress ain’t what it cracked up to be.
I borrowed a lawn mower last weekend (mine hit a tree root late last season and bent …something noisy) and was thinking how bad it would be if the fuel cutoff valve broke off in the closed position right as I was returning the mower to its owner. I’d closed the valve before loading into my hatchback but reasoned it must be a sturdy automotive grade thermoset plastic to withstand the fuel, heat, and impacts expected of a consumer lawn mower.
So you see, I had thermostplastic valves already on my mind.
My first thought was (unironically) “clearly what the OP wants instead of a thermostatic valve is a thermodynamic valve.” I ended up Googling it before realizing that it wasn’t a great search term for this purpose.
It is one of those annoying tradeoff problems. I have a heat pump HWS, so the water costs roughly one sixth to heat in the HWS versus a resistive heater. That saves a substantial amount of money over the life of a washing machine. Recently I added 11kW of solar on the roof. Daytime electricity is effectively nearly free. HWS economics are no longer such a big deal.
Eventually I will get a new washing machine, and it will probably only suck on cold water. It will only get run during the day.
There seems to be doubt in this thread that the temperature decline can be gradual enough to allow predicting how much time one has left. Perhaps this varies quite a lot between homes and systems. It’s gradual and predictable in my house, FWIW.
Cite? I’ve never heard of this, at least not in the US market.
The progress is that today you can get 50+ gallons of hot water out of a 40 gallon tank. Previously you’d get 40 gallons of hot water and then it would start its rapid decline.
I suspect the OP may have had a gas water heater in the past. Cheap ones just had (have?) a flue up the middle of the tank, so they can’t do any of the clever switching and stratification like a modern electric water heater.
Gradual and predictable here and my last house, too. You can start feeling it be less warm, then slowly approaches tepid, then cool, then cold. From hot to cold it takes, I dunno, four minutes plus or minus a minute?
I was going to say just use a regular mixing valve, at least you’ll be able to turn up the hot manually and know where it stands, instead of the valves thermostat doing it.
Also, the water in SA going into the heater may have been ~20’ F/10C warmer to start than the water in UK? So any new water going into the heater would not have been as cold to begin with and maybe less of a shock
in the past the only machines that did a “proper” mixed hot and cold fill were old Hotpoint and Hoover washing machines (distinctly British and British made) but now with no washing machines made in the UK there is no hot fill washing machine on sale in the UK. Yet.
