I have replaced a hot water heater, and I used a 12/2 wire to provide my 240 volt service to the unit. Is the 12/2 wire safe? Do I need to use 10/2 wire? There appears to be no service problems with the 12/2 wire.

To supply a water heater use # 10 gage/2 wire and a 30 Amp circuit breaker. A two element heater with 4500 Watt elements will pull 19 Amps when it's heating. Good luck, Tom

Tom is correct: the #12 wire will overheat and will be tripping breakers on you leaving you w/o hot water. 10/2 is definitely what you should have used.

All above is correct... just wanted to be clear that the breaker should be a 30 Amp DOUBLE POLE breaker... ;)

Just for future readers... ;)