This can save a lot of water if you're the type to let your shower run until it is warm. So some jurisdictions encourage their installation.
I've just started looking into either getting a tank-less water heater in the master bathroom or a recirculating system to save water. I like that the recirculating system would help with the entire house, not just that one bathroom, but it is looking to be quite expensive and wasteful of energy, unless we can do something like have switches in the bathrooms and kitchen to manually turn on the recirculator for a few minutes before use instead of running the water for a few minutes.
When you turn on the shower, the head operates normally while the water is cold. When the water becomes warm a valve in the head closes to stop the flow. There is a button on the head you press to open the valve, which then stays open until you turn off the water.
The idea is that many people turn on the shower to warm up but don't just wait around in the bathroom to jump in as soon as the water is warm. They go do other things like start their coffee machine or wake up the kids or check the news and weather. Between the time the shower warms up and they get around to coming to see if it is warm they might waster several minutes worth of warm water.
With this clever shower head they don't waste that water. Also, if they can hear the shower running from wherever they are doing other stuff when they hear it stop they know the warm water is ready.
This seems natural to me, but I've never met anyone else who does it this way.
At other apartments, I’ve had more involved systems.
This thread is making me think of that blog title: Reality has a surprising amount of detail.
So you should turn it off when you go on vacation.
It seems like a no brainer, but the prices are so high (like £700 / $900) that it would take many many years to pay back the cost, so it wasn't worth it.
As I understand it (and I am NOT a plumber) -- when you turn on the hot water, it pushes hot water up the line. Turn off the water, and that water will cool. But, if you add a one-way valve that allows flow from hot to cold, it will allow the higher pressure hot water line to flow into the cold water line so that it keeps hot water to the tap so that you don't have to wait (in my case) 5 minutes to flush out the cold water that has accumulated before getting to the hot water.
A plumber friend suggested this to me when I complained about my master bathroom (the furthest in the house away from the heater) taking SO LONG to warm up. Then he came out and installed it in about 15 minutes (which would probably amount to a one hour minimum charge for a plumber not doing it for free) plus a $10 part he had us buy on Amazon.
TLDR, now instead of taking 5 minutes to heat up from ice cold to warm to eventually hot, the hot water is warm from the second I open it, and hot within about 15-20 seconds.
