Thermosiphon (passive) Method
The easiest, most economical and desirable method of Thermo-coil water heating is the thermosiphon, using no pumps, controls or electricity. Heated water from the Therma-coil is less dense, lighter, and naturally rises to the top of the water-heater or storage tank. The cooler water in the bottom of the water-heater/storage tank is heavier and "falls" down the plumbing line to the Therma-coil, completing the cycle. The flow is slow and is reduced by long runs. This is only possible if the water heater or storage tank is higher than the woodstove and close to it. An ideal thermosiphon arrangement would be to place the water-heater on the next floor above the woodstove, in an attic, closet, or elevated in the garage opposite the woodstove wall (a stand can be built under the water-heater).
Sloping the piping at least 1 foot rise for every 2 feet horizontal run would be a good rule of thumb using 3/4" (well insulated) copper pipe. Soft copper reduces sharp turns and is easier to install in most situations. Local plumbing codes and methods should always be adhered to.