As you may know, an electric water heater can be 30% of your electric
bill...

Well I got to thinking... I have this nice woodstove which puts out a lot of
heat and it is always 80 to 100 degrees (F) next to the woodstove.

Is there some way I can use this heat to "pre-heat" the water going into my
hot water heater????

Well I came up with an idea and tried it out. It works!

I got a used 50 gallon water heater at a recycling center. Then removed the
sheet metal cover and removed the insulation. So now I had just a bare metal
50 gallon tank. I painted it black as in theory black absorbs heat better.

Then I placed this tank next to my woodstove. Then disconnected the cold
water going to my hot water heater and ran that to the bottom (drain)
connection on the tank by the woodstove. Then ran a pipe going out the top
of the tank by the woodstove to the cold water inlet of my electric hot
water heater. (Cold into the bottom, warm out the top.)

Note: My electric water heater is located on the other side of the wall next
to my woodstove.

After just a few hours, the water coming out of the top of the tank by the
wood stove was about 70 degrees. (The water from the city going into the
tank is 40 degrees F.) At this point the bottom of the tank felt cold and
the top was not cold.

The next morning, the entire tank was slightly warm.

Anyway I am now "pre-heating" the water going to my hot water heater. So
instead of my water heater having to heat up 40 degree water, it will only
need to heat up water which will be from 70-80 degrees. Perhaps warmer if I
have the woodstove going full blast and have not used any hot water for a
while. So should save some $$ on my electric bill.

Building code note: Now that I see this idea works, I'm going to install the
tank next to my woodstove to "code"* like a water heater tank would be. That
is drip pan, T&P valve, and strapped to wall for earthquakes. *I don't
suppose code covers anything like this? I also installed a valve and pipe to
outside for draining the tank.

Temperature and "steam" note: The temperature next to my woodstove never
gets above 115 degrees F. and water boils at 212 degrees. So no possibility
of steam being created.