I have a 12 gallon water heater with a 4500 watt element. It came with a 1500watt 120v element. Turns out all the water heaters use the same thermostat control, rated for 40 amps all I had to do was bump the wiring inside up to 10 gauge.
I have an expansion tank, shut off valve and local disconnect or vacation switch.

Why not put in one of those Marey gas tankless units? Same $300, saves space, and no pilot light. Even vents with standard B vent. Gas valve DOES NOT modulate, that's' why it's only $300. You must manually set the gas level yourself. Wouldn't want one as my main water heater, but for 1 bathroom not getting much use it would be fine.

https://amzn.com/B009EG4QJM

The 2.7GPM model is $232, might be enough for 1 bathroom.

https://amzn.com/B009EFVS8A

My wife isn't liking the 12 gallon capacity too much lol.
I say she was using too much hot water.
It's plenty for me but I'm trying to only use about 3 or 4 gallons.

Lowes has a 4.3gpm tankless gas water heater for $600. My wife said she doesn't want it that bad.
I calculate this heater can warm 40°F incoming water to about 102°F at a rate of 3gpm. So it would work great for a woman that loves to use hot water.

If I were to use this tankless one I would install it for the "back bathroom" temporarily, then make it the main hot water heater later on. I would still put this 12 gallon electric one in the back bathroom once it doesn't get used a lot.

I installed a 5500w heating element and magnesium anode.
Here are the old ones.
The original anode is aluminum and even after 2 or 3 weeks of use the heating element is covered with scale.

http://ecorenovator.org/forum/attach...1&d=1479668239