Electricity Saver Box Schemetic Instant Hot Water Heater Boxes??

Instant hot water heater boxes?? - electricity saver box schemetic

So, now do tankless water heater, which only a small box, the water is heated only when needed and I can not explain it to represent. They are only fields that make a huge water heater is very energy efficient. My question is this: your home with natural gas or propane is installed to one, or you can have a house of 100% of the electricity for the installation? In addition, they have had a significant energy savings and are very good, or have many problems? If my question is confusing, I'm sorry. My husband says that as a run on natural gas or propane in the house and I want to know if it was true preserved. Thanks for any help.