When does it pay to temporarily shut off electric tank hot water heater?

Motorapido

I've been occupying our vacation house four or six days/week. When I leave, I shut off the well pump and hot water heater (40 gallon electric). I'm wondering if I spend more to re-heat a cold 40 gallons of water than I save from turning it off for one to three days. Would I do better to leave it turned on? It's only about a year old so it should be relatively well insulated and efficient.

sunlight33

There is the risk of bacteria growth if you let it cool down for a few days.

STEVEusaPA

It really depends how much it runs to maintain temperature when your not home. Without testing, my feeling is it costs more to bring it back up to temperature. But if you have a leak, and the tank runs dry I'm sure it would at least damage the elements. See how long it takes for the tank to recover, do a little math. It's probably not enough $$$ to worry about it.
Me? I'd turn it off. I turn off my boiler (indirect), the water, and the gas when I go away for more than a few days.

ethicalpaul

There are curves that could be drawn and I wouldn't be surprised if the answer varied quite a bit depending on quite a few variables. In a modern water heater the standby loss should be pretty low. I wouldn't bother for a 3 day trip but I might for a week long trip (If I remembered to). But I wouldn't lose sleep over it, it's probably pennies.

If you have a lot of curiosity, you could put an electric meter on the heater and try it both ways.

There is the risk of bacteria growth if you let it cool down for a few days.

What about in the cold water pipes?

Larry Weingarten

Hi, Research was done years ago on this and what I was told was that if it's going to be off at least a full day, there are some savings to be had. If the ambient temperature around the tank will be cooler, the heat loss would be even more and turning it off makes better sense. Bacteria we worry about go dormant at cooler temps, so I'd be inclined to turn it off to prevent their growth in the heater or attached piping.

Yours, Larry

ps, Leave yourself a note just inside of the door that the tank is cold, so you turn it on right away when you come back

hot_rod

The temperature maintained in the tank, and the ambient air temperature around it would be the two numbers determining how much energy it takes to maintain. Hopefully it has heat trapper nipples or else a potion of the loss is in the piping also.
The indirect tanks like to claim a low standby loss of 1° per hour as negligible. However that is still 24° over the course of a day, so it does add up. I don't think electric tanks are insulated as well as indirect tanks?
I think considering the cost, adding an additional fiberglass blanket wrap may be worth considering. if you leave it powered on.

pecmsg

ethicalpaul said:

There is the risk of bacteria growth if you let it cool down for a few days.

What about in the cold water pipes?

Concerning Legionella ASHRAE recommends 140°F for a minimum of 1 hour to kill the bacteria. ASSUMING that has happened then legionnaires is not a concern.

In supply water the legionella bacteria is dormant if present at all.