A Woodstove Water-heating Attachment

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

CONSTRUCTION TIPS

The components of the heat exchanger system are shown in the accompanying illustration, but of course each installation will require some alteration of the basic dimensions. For example, if your stove is larger than ours, you might be able to enlarge the panel enough to get a full 60-foot coil of the 1/4" soft-copper tubing inside the up-sized exchanger framework. Those of you who have smaller heaters, however, will have to use a smaller amount of the line.

In any event, it's easiest to work with the tubing as it's been coiled for shipping. We just laid the curled line into the frame and gently bent the tubing to fill the rectangular shape. The flexible material can be arced down to about a 1-1/2" radius without kinking, so it'd not difficult to force it into any potential "hot spots". We worked from the outer edges inward, wiring the coils to the backing plate as we went. (Without the wire to hold the outer circles of tubing in place, the whole thing wanted to spring out of the frame.)

Once you get the copper tubing evenly distributed inside the frame, stir up a thin batch of plaster of paris and pour the mixture into the frame. Level the surface by running a straightedge across the angle iron, and allow the material to dry for a couple of days. Then the panel can be attached to the side of your stove, and the 1/4" lines can be plumbed to the preheater tank's 1/2" tubes.

SAFETY AND PERFORMANCE


We ran extended tests to determine the most effective configuration for the exchanger and to satisfy ourselves that the device would perform safely. For example, to see what would happen if a power failure shut down our pump, we sealed up the tubes exiting the preheater tank and installed a pressure gauge on the relief valve. The highest pressure we were able to develop in the system was 3 PSI . . . and that was after allowing flow to stagnate for eight hours at the highest possible burn rate for our Atlanta Stove Works Catalytic!

Also, to determine if conductive heat exchange through the wall of the stove was being encouraged to an unhealthy extent, we checked the inside of the woodburner's firebox each day for increased creosote accumulation. We found no difference in the appearance or depth of the deposits on any of the four walls, which suggested that the exchanger was receiving mostly radiant energy from the exterior stove wall. (The ceramic may have exerted some insulating effect, counterbalancing increased conductivity.)

How much hot water will the exchanger produce? Well, during a typical seven-hour cycle we would load 55 to 60 pounds of wood into the Atlanta Catalytic, which would boost the 42-gallon tank's contents to just short of 140 °F. This eight-pound-per-hour burn rate is probably somewhat higher than most folks use, so the volume of hot water that you might get from a similar unit could be slightly less. Of course, if you maintain a strong burn all day long, the total over a 24-hour period should still be more than 100 gallons per day of plenty-hot water. And even if you often operate your stove in a "closed down" condition, the system will significantly reduce your water-heating bill.

Depending on the size of your family and the amount of water each person uses, the system could eliminate your wintertime hot-water bill. Consequently, if you're able to get your wood at a price that's substantially lower than that of an equivalent amount of electricity or gas, the energy you put into warming water from your woodstove (which, of course, will be subtracted from the space heat the appliance would have delivered) will be well worth the investment. Besides, you'll have the satisfaction of knowing that you've taken one more step toward replacing nonrenewable sources of energy.

RSS | Comments | E-mail | Print