Actually there are propane tankless hot water heaters that only run on propane. I am not sure I have heard of electric only ones for RVs. A friend has an electric tankless hot water heater on the backside of his house and it needs 80AMPs of electricity.

Here is a link - http://www.tanklesswaterheatersdirect.com/shop/tanklesswaterheaters/precisontemp/rv500waterheatermainpage.asp

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-- Edited by bjoyce on Thursday 5th of April 2012 09:15:04 AM

From our experience with our DRV, the Suburban water heater that it came with,  is a lot like the 60amp endless water heater in our bricks & sticks. We have NOT run out of hot water with both of us taking back too back showers yet. When we first discovered this we were surprized and very happy. So we tested it on gas and electric with the same results. It do not matter which one we chose, it was endless hot water. 

You can find it here for 419.00 .

 http://www.adventurerv.net/suburban-water-heater-sw12d-direct-spark-p-27893.html

I believe washing dishes is a lot less water useage than taking a shower. But just to clarify, we take long showers without turning the water off. Not bragging, just trying to help.

So far everyone I have heard of who has an RV500 is happy with it. It should save on propane since you only heat when you use the hot water. Is the price difference worth it for cost savings, probably not since it would take a huge amount of usage to make up the $600 or so difference in price? But the endless hot water could be worth it to some. I wouldn't like it because we heat using electric most of the time and having a motorhome with a fixed propane tank it is a pain to fill propane.

MSinMS: If you have both the propane and electric switches on your water heater they will both heat the water at the same time. Depending on the set points of the two heating elements, one will top it off and the other will not. In our old RV we had a 10 gallon Atwood hot water heater and the propane set point was about 5 degrees higher than the electric, so if we had both elements on the electric rarely ran, so when on electric we would keep the propane switch off. Our current RV has a 10 gallon Suburban and the electric set point is higher so we can keep them both on if we want, but on 50AMP non-metered electric we normally only have the electric on. The electric heating elements on all of these hot water heaters, including the 12 gallon Suburban, are about the same size and use about 12 AMPs of 120 volt power. Our experience was that from cold water it takes 2 to 2-1/2 hours of electric to heat 10 gallons fully but only about 20 minutes of propane heating. With both on the time is closer to 15 minutes. Your two "long showers" are probably plenty of time to heat 12 gallons with propane but not with electric only. On full hookups sometime turn your bath faucet, not the shower, to full hot water and run out the hot water while on electric only. You will succeed in running out the hot water in about 5 minutes and it will take a couple hours to have really hot water again.

Everyone washes dishes differently. I can use up 10 gallons of hot water washing up when every pot is used, plus bowls, frying pans and the dinner dishes.