Automated shutoff of water heater after non-usage (for vacation home)

[SalamanderMan]

I have a vacation home with an electric water heater (50 gallon). There are times when it's not used for weeks at a time.
What I'm looking for is some way to shutdown power to the water heater power if no hot water has been used in over 24 hours, and when the hot water feed is used again, turn on the power to the heater.
 
I haven't seen any commercial item that does this.
 
I suppose to build this you'd need a flow sensor that can detect the use of the hot water feed, a 220v relay and automated controller.
 
Any thoughts on how to do this?
 
(At the house, there is no propane or gas, and I don't want to spend the money for an instant-on electric water heater that can support a 3 bedroom house.)

 

[ano]

Can you tie it to something else, like occupancy?  If you have to use water before it turns on, you will get cold water and have to wait hours for it to be heated.  That's a long time of running the water and waiting until it heats up again.
 
Also, be careful with this. I don't know how cold or hot it is around your water heater, but I used to turn it off nightly here in Phoenix.  Over time the thermal cycling causes leaks.  I had two replaced under warranty luckily, but they leaked way sooner than I thought normal.  Also, of course, freezing may be a problem.  It might just be better to insulate it and leave it on all the time. 

 

[jlehnert]

Agreed.  If you can tie it to occupancy, it would be much easier.  Whenever I set the alarm to "vacation", the system automatically turns off the water heater, and turns it back on when the alarm is disarmed.  I have a gas unit, so I use a simple appliance module on the starter circuit,  but the concept would be the same for your electric.

 

[tmbrown97]

As far as how to switch the power, Elk makes something just for this purpose (can be used with any technology).
Elk 9200 Heavy Duty Relay Contactor
 
This thing just gets plugged into a switch of any sort - be it a Z-Wave or Insteon or UPB module, or simpler.
 
Do you have any automation in place there today?  Internet?  What OS does your phone use?
 
You could even just set that contactor up to a WeMo Switch - when the WeMo Motion hasn't seen movement in 24 hours, cut power; when it sees motion, make sure power is on - and you can remotely trigger it while you're on your way from your phone - or even go further and have it automatically turn on based on a calendar item or location sensing using IFTTT.com

 

[SalamanderMan]

Thanks for the above suggestions. The house does have a land-line, but has no internet (can't get, even satellite), no cell phone access, and no current automation.
 
I want this as simple as possible, completely automatic. I also have a property manager rent out the house, so I can't easily (and don't want to) track when it's occupied.
 
And yes, I realize that it can take a while to heat up a water tank (my experience is about 30 minutes to warm, and 90 minutes to full hot).
 
I like using a motion sensor instead of a flow sensor, especially since it avoids plumbing.
 
This can probably be rigged with no automation: a power supply, a flow sensor, and a time-delayed relay. Every time the flow sensor is triggered, the relay is reset.

 

[SoulkeepHL]

Just throwing out an idea that would add some serious complexity, but you might consider looking into stepper motors to simply turn the water heater to the "Vacation" temperature, instead of turning it completely off.

 

[tmbrown97]

Thanks for the above suggestions. The house does have a land-line, but has no internet (can't get, even satellite), no cell phone access, and no current automation.

My kind of place!

Up to you - the Belkin option requires zero plumbing and can be just as standalone; not sure if it can work disconnected from the cloud or not; Z-Wave would work just the same, or UPB or any other technology.