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Posted by TKM on March 28, 2008, 12:34 pm
> 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.
>
Sounds like a great idea to me. That tank of warm water (I think such a
thing is also called a "tempering tank") also radiates heat back into your
space when the stove fire goes down and so the room should hold a more even
temperature. It's also an emergency water supply -- assuming you can get
the water in the tank out with no watter pressure if, for some reason the
main water supply fails.
Living on a farm many years ago, we had a similar arrangement. The
uninsulated hot water tank was placed next to the coal furnance to soak up
radiant heat and a loop of steel pipe went from the tank through the fire
box in the furnace to speed up the process. There was an auxiliary kerosene
heater also connected to the tank for heating water in the summertime.
TKM
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