The energy source for a power vent water heater depends upon a lot of factors.
It also depends upon the company that is releasing the product.
However, you should keep in mind that most of the power went to water heaters that do not need electricity.
This is because it has a power vent which helps it function.
You have to consider the source of energy before getting your hands on the water heater if you want to avoid any kind of inconvenience in the future.