Paragon 8145-20 is a 240V defrost timer
It is probably not best choice for water heater timer
Timer initiates defrost cycles each 4 hours.A water heater timer should have more scheduling options
-For example estimates show average run-time for water heater is 3 hours per day, depending on incoming water temperature, thermostat setting, and number of gallons used.
-To save money using water heater timer, you have to schedule times carefully so water heater runs less than 3 hours per day.
-Now your average electric water heater heats about 20 gallons per hour.
-Average shower uses 4-9 gallons hot water, so water heater needs to run 15-30 minutes (15 summer, 30 winter)
-Average bath uses 12-15 gallons hot water so water heater runs 45-60 minutes
-But lets say you run water heater for 1 hour and make 20 gallons of hot water. Then you take a shower, expecting hot water to remain in tank.
-Here's the problem ... cold water entered the tank to replace the shower water ... and the new cold water is cooling the rest of the tank.
-So a timer means scheduling hot water to match shower and bath events. For example taking shower and bath in immediate succession.
-Or set the timer for each individual hot water event ... for example set timer for 1/2 hour for shower, and later timer turns on 1 hour for bath, or 1-1/2 hr for 2 baths, etc
-> The flexible programming described above is not a characteristic of defrost timers.
I suggest Intermatic WH-31 240V or Intermatic T-104 240V or GE 15207. These are mechanical repeat-24 hour timers with manual override where each day has same schedule.
Digital programmable timers like Intermatic EH40 offer 7-day, 40 event programming. Weekends and weekdays can be different.
To see several box-type timers:http://waterheatertimer.org/Boxtype.html