This may sound silly but you could try filling your hot water heater with whatever but not turning on the propane. Then flip the switch in question and come back two hours later and see if you have hot water. Or if you have and in line electrical consumption meter like the one I got from Harbor freight for $15, you could fill the hot water heater with water just to be safe, and observe any change in electrical consumption before and after flipping the switch. My aftermarket electric hot water element only draws 450 W, but factory option heaters tend to be significantly more