# solar batch heater



## kendall j (Mar 30, 2007)

I have two old gas water heaters I want to use the cores to make a solar batch heater. Everything I find talks about using cores form electric heaters. Is there a problem with gas cores or will they work fine? 
Thanks.

Kendall


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## greg273 (Aug 5, 2003)

The only difference is the flue pipe going up the middle of the gas tank, as far as I can tell. Other than that, a tank is a tank.
I've been thinking about this one too, and trying to design a tank/collector setup. So many projects, so little knowledge.  
Having said that, theres no way I'm going to let all that solar energy go to waste! So, onward!


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## Windy in Kansas (Jun 16, 2002)

I consider this to be an older (1983) but really good book on the topic of solar water heating for the do it yourselfer. It is a Rodale Press book which is a company/organization that I respect highly.

Along with charts and useful information the book has excellent plans for a batch heater that uses a cusp reflector. Plans were made and perfected through the building of a number of units according to the book. 

I've not built the unit but the plans will be the ones I use when and if I do build one. Best I've ever seen.

The Homeowner's Handbook of Solar Water Heating Systems: How to Build or Buy Systems to Heat Your Water, Swimming Pool, Hot Tub or Spa (Hardcover)
by Bill Keisling (Author)

You may wish to peruse the book through an Inter Library Loan if your local library does not have it.


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## SolarGary (Sep 8, 2005)

Hi,
Here is a really good book on building batch heaters:

http://www.builditsolar.com/Projects/WaterHeating/ISPWH/ispwh.htm
A free download

More plans for batch heaters:
http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm#Batch

Gary


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## wy_white_wolf (Oct 14, 2004)

As Greg mentioned the only real difference is the flue pipe. But it does effect effeciency of the system. The flue pipe increases surface area of the tank without increasing the area of solar input. This translates to increased heat loss from the tank. With working with a small input systems as solar the increased heat loss can greatly affect the performance of the system.

Now if you fill the flue pipe with something to serve as thermal mass you may illiminate (sp) that problem.


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## kendall j (Mar 30, 2007)

I wonder if instead of thermal mass maybe putting insulation in the flue would be better since the flue won't be getting direct sun. Any thoughts?

Kendall


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## SolarGary (Sep 8, 2005)

kendall j said:


> I wonder if instead of thermal mass maybe putting insulation in the flue would be better since the flue won't be getting direct sun. Any thoughts?
> 
> Kendall


Hi,
My 2 cents would be that insulation would be better. 
It seems like it would be better to limit the thermal mass to the water itself.

I am tempted to think that the gas tanks might actually work better than an electric tanks. A (say) 50 gallon gas tank has to be a little larger in outer diameter than a 50 gal electric tank to make up for the water volume lost to the flue pipe. This slightly increases the area that the sun shines on, and therefore the solar gain. If you stuff the flue with insulation to prevent loss from the flue, it does not seem like there would be much of any heat loss penalty. Some of the better commercial batch heaters uses 4 or 5 small diameter tanks in a row -- I would guess that the benefit of this is to increase the ratio of sun gathering surface are to water volume -- you get a little of the same effect by using the gas tank.

In any case, I don't see why it would be a big factor either way -- If you have the tanks, and they are in good shape, I'd go ahead and use them.
Things like how you design the box, insulation, reflectors and glazing will make a more difference (I think) than gas vs electric tanks.

If you have not taken a look at the free book on batch heaters by Bainbridge I mentioned above, its a gem.

Gary


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## raymilosh (Jan 12, 2005)

There is an article in an old issue of Mother Earth News where folks welded fittings on the ends of the tank to create a watertight tank out of the cylinder running through the water tank. It created a heat exchanger. Antifreezew was run through a flat plate collector and through the inside cylinder and potable water was run through the original tank. the article is available for free on line. http://www.motherearthnews.com/article-categories.aspx. Just a thought. 
Also, having made a batch heater here in NC, I suggest plumbing 2 tanks in line, having nighttime insulation for winter, making it such that the tanks are easily replaceable (they are old and discarded, after all), making it in such a way that when it springs a leak, it won't damage your house, protect the lines form freezing and finally, consider buying the cheapest new water heater tanks you can find...they'll last way way longer.


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