-> O.K. I am intriqued. Does this system work with a system where the he
-> source is below the heat exchanger???
Let me throw in a penny or two of thoughts, but first a question.
You want to store heated water in a tank 20 feet above the heat
source?  The normal convection should provide some circulation.
If you have a vertical run of pipe, and a vented tank, then there
may be a cheap way to increase circulation.  Insert a small amount
of compressed air into the up-flowing water.  The air rising in the
pipe will increase the circulation a fair amount.  A small and
inexpensive diaphragm compressor is cheaper to buy and run than a
pump.  And seals aren't anywhere near the problem as a pump has.
The bubbling noise may be objectionable.  And it may not be enough.
But, it's an old and somewhat effective method.
-c-
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