On Sat, 30 Jul 2005 15:28:24 -0500, "Chris
wrote:

It is impossible to set the two tanks at the same hydrostatic height in
order to stop this natural transfer.

Can you mount the immersion tank _above_ the fire tank ?

With my experience of solid fuel waterheating, I've never been short of
heating capacity when the fire was lit and I've often been short of HW
storage after the fire had gone out. I'd have no problem with the fire
always heating both tanks, with thermosyphon circulation between both.
Obviously having the immersion in the upper tank and discouraging
circulation would be an improvement from that point too.

Another solution might be to rename the upper tank "single", the lower
tank "extra" and fit an immersion into the upper tank. Use the pump when
you want extra HW storage, otherwise just use the upper tank for
everything.