$2.00 is your current rate if you needed propane today? If so propane is slightly more economical. Propane hot water heaters ( tank type ) have a .65 EF electric is about .92 EF. Heres a spreadsheet to plug some numbers in: www.eia.gov/neic/experts/heatcalc.xls make sure you put in the correct EF for electric and propane. In your case propane is about 15% cheaper at that rate. I doubt your current system is at a .65 EF I suspect its much lower.