Originally Posted by PolarisGuy
Ours has the option for both. We have a electric switch inside the rv in our control panel cabinet. I personally use propane when I can cause it heats it up much quicker. I believe our unit will only work on one or the other. When we are full hookups I will usually set to electric as soon as we are setup and it works alright.
It can work on one or the other, or both simultaneously. It's explained here in more detail:
Suburban's electric switch and much more
Even if you have both the electric and propane/DSI switch on the inside of the RV, they both can used simultaneously to get the fastest heated water. This is good if several people are taking showers in succession.
We talked about recovery rates recently here:
water heater question