I have a propane water heater right now. I live in the middle of nowhere and have my water heater and furnace on propane. I also have a heat pump on my house that heats the house when it is above 20 degrees outside and an Englander wood furnace tied into my duct work. So right now I usually heat my house with wood when it is under 20 degrees and my heat pump when it is over 20. I only run my propane furnace when it is really cold out.

So I filled my tank last summer when propane was 1.50 a gallon. Right now I need propane and the cheapest is 3.50 a gallon. I need propane within a couple weeks or I am going to run out and have no hot water.

I do not want to fill my tank right now, I want to wait till mid summer when it drops in price. And from now on I only want to fill my tank once a year only when it is cheap.

I have more than enough room in my 200 amp breaker box, so I think I will put in an electric water heater. What I would like to do is be able to have both a propane water heater in case we lose power, and an electric to run most of the time otherwise. It would also be nice to have an extra one I can fire up in tandem when I have house guests come stay with me for extra hot water.

So I want to plumb my electric water heater on top of my already existing propane one. And I would like to put in valves to be able to run either one. I also thought if I'm leaving my propane tank in place, I could use the propane tank as a tempering tank to bring the water to room temperature before it goes into the electric water heater.

I made a drawing of how I'm thinking of plumbing them together. I hope it makes sense, but I want to be able to use valves so I can either run them in tandem, or be able to cut the electric one off altogether and just run the propane one if the power is out.

I have well water on a water softener. I have a generator backup for my well pump, so I do have water if the power is out. The propane furnace was new in 2011 so it's pretty new and it's a Ruud Pacemaker LP series. The electric one I bought is a Whirlpool Energy smart water heater.

I hope my drawing makes sense, what do you guys think?

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And also I thought I would add, it's cheaper right now to buy a electric water heater and install it, then it is to fill up my propane tank with the higher prices.

I have a 500 gallon tank, and propane is 2.00 more a gallon than it is usually in July. So if I fill up right now it would cost me a $1000 more than what it would in several months. I bought a electric water heater and all the stuff to install it for $600. So I'm already $400 in the positive by doing this.

Also I did read that I should switch the anode in the propane water heater to the exact same as what's in the Whirlpool water heater I just bought. I read somewhere if they are different, they can hurt each other.

quote; I read somewhere if they are different, they can hurt each other.
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I don't know where you would have read that, but the anode rod only "affects" the heater it is in. Your drawing shows and/or for the electric heater and if that is all you are concerned about, a "three way valve" in place of the tee will accomplish that. Any other configuration and you would need a lot more valves, or a few 3 ways.

Exactly like the water heater bypass set up in my RV, so you can take the WH out of the loop when you pump antifreeze in. Looks good, I would say you only need one valve on the hot output of the propane WH between the pipes going to the electric WH.

the only gas appliance i have in my house is a propane range.
i paid 5.42 a gallon last november.
your drawing looks to me like it will work fine..

The OP states he has a well which would indicate he should already have a storage tank which could normally act as a expansion tank.

I have seen other posts concerning the use of a expansion tank on other than well systems. Not being a plumber, and not familiar with code or the actual safety implications of when such tanks are needed I wonder "if" one would be recommenced for this installation.

From the OP diagram it is possible for the electric tank to be isolated from the main plumbing system --- possibly with power on. Will the electric tanks Temp/pressure relief valve be all that is needed -- or from code / experience should a expansion tank be included in this installation?

You seem to be answering a question which was not asked, and giving a solution to a problem that does not exist.