Obo, thanks for the pointers. I have a few questions. 1) Do you recall the material and ~size suggested for the fire box? 2) You say "fill the walls with sand" and later "fill the cinder block with sand" -- is this the same step? or do you mean that the void space in the cinder blocks and the space between the cinder block and fire box are all filled? 3) do you think the sand will get hot enough to damage solder joints? 4) do you think there is a balance in the fire box size and the amount of copper piping? 5) can you direct me to more information?Obo said:There is a description of how to set up a roof top solar hot water system in the book Back to Basics.
If you have free firewood this one is good. Build a well pump house size building out of cinder blocks. Fill the walls with sand. Build a fire box vented to outside the cider building for inflow and out flow of air and exhaust. Make sure there is a doorway to feed the fire box from the outside of the cinder building. Then put a system of copper pipe inside the cinder building running into the house and tank. After you have done that fill the inside of the cinder block with sand. I am not sure if they used regular sand or green sand.
When you have this completed you start up the fire heat the sand and the water gets hot in the pipes flows out to the tank. From my understanding you don't have to keep the fire going constantly as the sand holds the heat. The guy talking about it said he heated it only every three days sometimes.
There are other technical things you may need to think through. The above is just what I remember from seeing it years ago.