Installing timer in heater saves energy
If you turn your hot water heater off during the day, won’t it cost more because you then have to heat up the whole tank and wait minutes before taking a shower? Also, isn’t it kind of an inconvenience?
No, water heater energy consumption increases with higher water temperatures, and water heaters use more energy to heat water up and keep it hot than they do to heat it up once, because heat is lost through the walls of the tank in proportion to the tank temperature. The same energy is required to heat up the water regardless of whether it is heating a little bit at a time, or all at once. Heat losses through the tank walls or pipes simply add to the cost. So, turning the water heater off for a few hours each day actually saves some energy. This strategy works best for electric water heaters, because they lose heat less rapidly than gas or oil water heaters.
If you turned your hot water heater off during the day, it would be an inconvenience if you use more hot water than is stored in the tank. Installing a timer that turns the water heater off or that lowers the temperature during the night generally poses no inconvenience at all. These timers can be set to turn the heater back on an hour or so before you get up in the morning, so your hot shower is ready to go when you are.
Source:radiant-heat-floor-methods.com