You also need to figure how how much energy it takes to heat a tank full of COLD water, compared to warm water. If you use a vacation setting, the temperature is probably 110°-120°F.

Personally, I wouldn't turn the water heater off UNLESS I also drained it because of the potential for development of Legionella bacteria, which can lead to Legionnaires' disease. This bacteria has been found in warm water in hot water heaters.

-Grainlady

fwiw...
I don't know how many but there are bunches of homes with time clocks on their hot water heaters.. Many only run for minimal time once per day for many many year. They dont seem to be having any epidemic of deseases from it.

I don't use hot water except for the shower - I dont need hot water at all right now during summer.. Florida.

I flip on a 40 gal hotwater heater for 35 minutes and then turn it off ...before I get into the shower. Been doing this for 12 years.
One heating gives me pretty much a max of three showers over three days. It's wrapped in fiberglass and also reflectix with some styrophone air gap spacers under it.

A few things to keep in mind.
-Gas heaters have vented losses of heat which electric heaters do not have.
-Gas heaters heat from the bottom while electric heaters heat primarily from the middle with supplemental heat from the bottom.
-One source I read, although it was a utility, claimed that 100 people per year in Quebec are hospitalized from bacterial infections resembling pneumonia caused by inhaling tainted water from showers, hot tubs and the like. Is the source credible? I'm not totally sure but what I've read is interesting in that Canada is much more concerned about bacteria, while the US is more concerned with scalding. Each person has to decide which is more important to them.
-How much will you really save? If you have it well-wrapped and insulated to minimize heat loss the effect of turning it off, especially for just a day or two is minimized.
-Other sources claim that the higher temp in an electric heater is better for maintenance of the unit. I'm not well-versed in electric water heaters but have been looking into them more lately as I'm considering getting a place with electric heat.
-Gas heaters will actually help maintain and can even increase the temp from the pilot light running so if you have gas, there might be no benefit in turning it down. When I leave for several days I seldom turn it down since I don't think of it. I read an interesting article about a guy heating his water solely from the pilot light.

Some temp info:
* 70 to 80 °C (158 to 176 °F): Disinfection range
* At 66 °C (151 °F): Legionellae die within 2 minutes
* At 60 °C (140 °F): Legionellae die within 32 minutes
* At 55 °C (131 °F): Legionellae die within 5 to 6 hours
* Above 50 °C (122 °F): They can survive but do not multiply
* 35 to 46 °C (95 to 115 °F): Ideal growth range
* 20 to 50 °C (68 to 122 °F): Legionellae growth range
* Below 20 °C (68 °F): Legionellae can survive but are dormant

FWIW, for about the last year or two I've turned my water heater from about 120° up to about 130° and occasionally up it to about 140°-145° when I have some laundry I want to be in hotter water.

One side note is a reminder to maintain your tank heater. Drain off some water every few months to keep the sediment from building up. Sediment can not only make your unit less efficient, it can actually damage your heater.

Oh, as far as will a lower temp give you enough hot water, that depends on how much "hot" water you use and the size of the tank you have. Are you being supplied sufficiently now?

You might want to get a meter and hook up and see what you actually use over a two day period without water use. That will tell you what it costs and you can also check the temperature afterward to see what the benefit could be. While I'm hesitant to worry too much about the temperature being lowered, at the same time, I'm skeptical that you'll save a dollar or two a day just on standby losses. And of course there is the issue of reheating the water after the shutdown assuming there is such a heat loss. I do think I'd aim more to keep the heat loss to a minimum.

Several years ago the city power and water utility, on my request following their promotion, came to my rented townhouse
to install an insulation blanket around the cover of the tank, and a timer to allocate power to heat the water at 2 a.m., when
demand was low, resulting in surplus generating capacity. There was an over-ride button to allow the householder to call for
immediate power in case there was a heavy demand for hot water, due to washing of dishes, clothes in addition to multiple
showers, etc.

Later, when the system was taken over by one operating over a wider area, when we made a service call, they removed the timer
and were removing the extra insulation blanket and I told them to leave it there ... then I reinstalled it.

When I called their office to complain about the removal of the timer, I was told that they did not offfer that service ... but
they had no satisfactory answer when I asked why they didn't offer it. They appear to be only mildly interested in spreading
the demand for power, related to energy conservation.

We in the western world have a lot to learn about the realities of life that operate in about 4/5 of the world ... and
we're going to be learning it ... have you noted how our high-profile employment positions are being relocated to lower-wage
areas?

I've said a number of times here that 70 years ago there was a horse-drawn covered wagon that hauled ice down most streets
in many cities to deliver ice to householders' iceboxes, a couple of times a week: other similar wagons carried milk and bread.

About sixty years ago they began to build refrigerators.

If you ask some old-timers around you, they'll tell you that refrigerators built 50 years ago lasted for 40 years.

Modern engineers being stupider, it appears ... refrigerators that they build now last for 10 years ... if you're lucky.

Considering the resources needed to provide metals and plastics to build them, plus the costs of smelting, delivery,
etc., our increasing shortage of energy, plus increases in global warming and pollution to build a frig, need to tell us that
we should require those same engineers to build an energy-efficient frig that'll last for 50 - 70 years.

Plus ... at the wage levels that our kids and grandkids will be getting, they won't be able to afford a new one every
10 years - or even 20 years.

The playing field is getting levelled ... and those in our part of the world who got used to living high on the hog for a
couple of generatios are going to find that it hurts to get used to living more simply, again.

Have a great weekend, everyone.

ole joyful

We have never turned off the hot water heater. I agree with the others - the tiny savings isn't worth wondering what is "growing" in the water.