I would love a way to turn off my electric hot water heater between the hours of about 10pm and 7am.
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 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.
On weekdays, my price of electricity from 11pm to 7am is about 4 times cheaper than from 7am to 4pm, and about 10 times cheaper than from 4pm to 9pm.
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.
To understand how this works it's important to know that temperature loss is linearly proportional to the temperature difference. Insulation reduces the ratio independently of temperature.
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).
Insulation is worthwhile, but has nothing to do with what you are asking.
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.
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).
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].
No, that is still not true, no matter how good the insulation.
> 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 have anything to support that claim? Because in my belief this follows normal thermodynamics, which means that if the energy dissipation over an amount of time is less than the energy cost to heat, it makes sense to do it.
Do you think there is no relation between the thickness of the insulation and the time it takes before reheating is more energy efficient?
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.
Per @quickthrowman recommendation I can add that this is the way to go for an electric hot water heater having installed many of these Intermatic time clocks. The old ones were analog and one can hear a clicking but they do make them digital now, YMMV.
I use a $8 programmable plug timer switch off Aliexpress to do exactly that. But it's only useful when I live alone. When a girlfriend is living in, messing with hot water supply is an absolute no-no!
Depends… if you like to take your showers at peak times, the tankless might cost you more in opex (in addition to the capex).
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 if you go that angle the capex on a heat pump heater regardless if hybrid or pure electric is going to negate any savings, those are typically 2-3x of a higher quality brand traditional water heater.
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.
The cheap ones are fairly common in Britain where the user isn't choosing (student houses, cheap rentals etc). The installation cost is low, but the running cost is high.
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.
Yes, You can buy an electric tankless but just be extremely informed of the large amperage requirement to instantly heat your selected gallons per minute flow.
Yeah you can find them on the Home Depot site. The largest ones use 36kW which is beyond a typical residence's electrical service. It doesn't save you any money if you need to upgrade your electric service.
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.