I also have the Aqua Hot 450D. In the "Burner" mode you use diesel fuel to fire the Aqua Hot burner. In the electric mode you are using the electricity to heat the fluids in the Aqua Hot. The electric mode will use around 14 Amps while operating. The burner mode will use approximately 0.4 gallons per hour depending on the cycle of the burner. The more cycles, the more 10ths of gallons will be used per hour. The burner mode works off of 12v and draws approximately 4 amps.
On a trip the engine will provide hot water and there is no need for either of the Aqua Hot switches to be on. When we stop and are plugged into campground electricity we use the electric mode. In the morning DW will turn the burner on. With both electric and burner on you will have continuous hot water. Very nice for showering. When we are finished showering we turn the burner off.
From the expert in my area:
"In cold weather: If no one is in the coach, electric on, open cabinet doors under sinks down to 30 deg F. Below that add diesel. If in the coach, add diesel to electric when temp is below 50 deg F."
In the basement on the Aqua Hot panel there is a rheostat. It should never be set below 40˚F. During this last freeze our temperatures here dropped to 19˚F. I had increase that rheostat to 50 or so degrees. When I checked with a thermal gun the temperatures in the bays were all above freezing. Thank you Winnebago.
On a side note: Your generator can be set to run in "auto" mode. You can set it to come on when battery voltage is low, when electricity goes out, or when not plugged in and there is a demand on the air conditioner. There may be a few other "auto" settings, but those are what I use. If you are boondocking be aware of the 14 Amp draw using the Aqua Hot electricity. I would only run that mode with electrical being supplied to the RV.
Wayne MSGT USMC (Ret) & Earlene (CinCHouse)
2015 Winnebago Tour 42QD 2008 Winnebago Destination 39W
(RVM-14) It is what it is, and then it is what you make of it.