Nope. You won't save anything (at least nothing that is noticeable). You are still using 'X' number of gallons of hot water per month and it takes a fixed amount of energy to heat the incoming cold water to the storage temperature. Even if you are just using the upper element, you are still really heating the whole tank. Heat moves from hot to cold, so that hot water that is sitting on the top is going to cool down while transferring energy to the cold water on the bottom. So when nothing is being drawn from the tank, the top element will continue to cycle ON to heat up this upper layer of fluid until the entire tank is hot. In addition, even if you are thinking that doing this will reduce standby losses by lowering the average tank temperature, you have to remember that electric tanks are very well insulated and the cost of storing the hot water (at normal temps) might be $20 or so per YEAR. So even if you saved anything by doing this, you might save $5/year or less.
Better options:
- turn down the temperature on the tank (if greater than 130*F)
- insulate the hot water lines that you have access to (get 3/4" foam, not the cheap 3/8" stuff).
- use less hot water (turn down the temp in the shower, use a lower flow shower head, take shorter showers, etc.)
- a recirculation system or point-of-use small tank heater may save some money is you have some long runs from the water heater where you constantly have to run the hot for an extended period before the hot water reaches the tap
- could add a blanket to the WH, but it is not needed in most cases (especially if it is a newer WH)
- add a solar setup to pre-heat the water (may or may not be cost effective)
- look into drain water heat recovery (
http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13040)..several posts on here (terrylove.com) by memeber "Dana" on the subject
Basically, you are best off using less water that needs to be heated than trying to reduce standby losses.