Therma-coil Woodstove Water Heating

PLUMBING

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.

Pumped (active) Method

When the water heater isn't located close to and higher than the stove, a small circulator pump and controller is used. The differential controller compares a probe sensor inside the bottom of the water heater / storage tank, and a probe sensor inside the therma-coil exit line. Whenever the stove water is hotter than the storage tank, the controller turns on the circulating pump. The pump circulates the cooler water from the bottom of the water heater, through the Therma-coil where it is heated, and back to the top of the water heater (costing only pennies a day in electricity.)