12.5 Kwh per day
375 Kwh per month.

750 Kwh per two months.


Just to make a point:

My entire electric bill for a two month period is 750 Kwh on a four bedroom colonial with typical appliances and a gas stove. The usage rises to 900 Kwh in the summer months when the window a/c is in use.

I think your experience must be significantly in error. There is no possibility of saving this amount of energy unless you're using thousands of gallons of hot water and your electric bill was 2000 Kwh per month prior to the installation of the tankless heater.