[David Carrol]

I'm not sure you can compare costs as the most efficient way to use the aqua-hot is a combination of both. To my understanding, Aqua Hots were not designed to run only on electric to give you all the hot water and heat you need. The electric alone cannot keep up with the daily water and heating use in a cold environment. At times you have to use the diesel to have hot water for a couple of showers.