I see no reason to keep the water hot during the time absolutely nobody needs it, and we know it will take less energy to heat it back up again rather than keep it at temperature.
Also, yes, I have turned the temperature down as low as it will go.
The contents of the box are
1. A programable timer light switch: https://leviton.com/products/vpt24-1pz
2. A 120 volt controlled contactor. I'm not entirely sure which one it is, but I think it is https://ca.rs-online.com/product/eaton-cutler-hammer/c25bnb2...
The box has a 240 volt circuit and a 120 volt circuit into it. The 120 volt circuit is connected to the programable timer light switch, which is then connected to the control inputs of the contactor.
The 240 volt line connects to the contactor and then on the other side of the contactor it connects goes out of the box and to the water heater.
For me I've programmed my hot water heater to turn off from 4pm to 11pm on weekdays, which avoids heating the water during peak time of day rates at my location. (I typically shower sometime during that period.)
I can open the box and press the switch on the timer if I ever want to temporarily override the program.
That all said, I don't have any measurements to tell me if it is worth the expense. Although it is quite clear from my hourly power usage when the hot water tank switches on at 11 pm.
I wonder if it would be worth keeping it off until sometime in the am the following day - do you need piping hot water from 11pm until about 5am?
Also I usually run the dishwasher and laundry sometime after 11pm, so it is usually helpful to have hot water available overnight.
Edit: I should mention that I have a ventless combo washer/dryer, so my clothes come out clean and dry in the morning. Unfortunately they are not folded.
If you are heating a house, or a water tank, or anything, it requires much more energy to keep it at a constant temp 24x7 than it does to let it cool down when you don't need it hot, and then just heat it back up again later.
That is why "smart" thermostats like the Nest became so popular. No need to heat your house while you are away during the day. So let it cool down a bit, then just warm it back up again soon before you come home. Much less energy used.
My Quooker is so well insulated, that you should only turn it off if you aren’t home for a week. Otherwise is exactly counter to what you say: more energy efficient to keep it at temperature instead of letting it cool and heating it again [0].
> That fully depends on the level of insulation. Newly build houses here in The Netherlands rarely cool down when heating is off, and the temperature stays generally stable, even when you are out (and the heating is off).
Even if it's a few days, and it does drop a few degrees, you still spend less energy bringing it back up to whatever temperature than you would have to keep it there the entire time.
Do you think there is no relation between the thickness of the insulation and the time it takes before reheating is more energy efficient?
As an approximate example, suppose if takes one hour for the tank/building to reduce to a thermostat set-point 10% lower than the 'high' set point. Further assume you could use that lower set point for 11 hours, so the tank/building temperature is 10% lower for a full 10 hours. Finally, assume increasing the temperature of the tank/building by 10% takes one unit of energy.
In order to maintain the low set point, the first hour is free since we are losing temperature. The middle 9 hours need (190%) = 0.9 units per hour for a total of 8.1 units. In the 10th hour the low-set point scenario needs to warm up to the high set point and overcome heat loss so that individual hour requires more energy than the high set-point scenario: (1110%) = 1.1 units for that single hour to return to the high set point.
In total the low-set point needs 0 + 8.1 + 1.1 = 9.2 units of energy over the 11 hours.
For the full 11 hours the energy required to maintain the high set point is 11 units (1 unit per hour to make up for 10% loss).
If it’s larger than 40A @ 240V, you could buy a 120v astronomical time clock switch and use the output of that as the input to a 120v control coil for a contactor sized for your water heater.
Generally you want your water heater to keep the water hot enough to kill any bacteria and prevent their growth.
The old (pre-electronics) ones are easy to understand — the heating/water comes on (in this case) at 10:00 and goes off at 16:30, then goes on again at 21:00 and off at 07:00: https://www.alamy.com/stock-photo-timer-control-for-hot-wate...
I think it comes down to heater size and voltage - mine is only 60 liters and 220V so can use regular wiring and amperage.
More and more “tank” water heaters are moving to heat pumps which should use less electricity overall than a tankless (if you can handle the possibility of running out of hot water).
Which full circle going back to the original discussion of turning off the heater. You probably end up close to no/low savings. I can see an argument of a smart heater being able to slightly adjust load at peak times but I engineering a heater to turn off when you are sleeping and then heating back up before use is probably going to not have much savings. Those heaters are increasingly made to edge out at maintaining the heat and take quite a few hours to heat up.
They are crap. 8kW is typical, and the pressure for a reasonable water temperature is low.
I haven't knowingly used a more powerful one. I suspect that would negate the cheap installation cost, as it would need a three phase circuit.
https://www.homedepot.com/p/Rheem-Performance-36-kw-Self-Mod...