TESTING CREOSOTE-REDUCING DEVICES: THE RESULTS

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The Smoke Dragon is the largest of the three products we examined. It comes equipped with a variable-speed blower, a conventional damper located above the device, and a secondary air port which delivers oxygen to the combustor.

TEST PROCEDURE

Our approach was to expose the test installations to ten days of typical stove operation, and to use the weight changes of the chimneys as the measure of creosote accumulation. Two examples of each product were tested to insure scientific accuracy, and two controls (installations without the add-on devices) were fired simultaneously to provide a basis for comparison. (The testing was done in two stages. One series used two pairs of stoves set up with Smoke Consumers and Smoke Dragons and one pair of controls. The other included two stoves fitted with barometric draft controls, and two unequipped units . . . the same two control stoves as in the other series.)

The test devices were installed on identical woodburners (Fisher Baby Bear models) with identical chimneys (manufactured by American Metal Products Co.) and stovepipe connectors (made by Dura-Vent Corp.). Since air leakage anywhere in a stovepipe or chimney would have caused a change in the rate of creosote accumulation, we needed to be sure that no one system leaked more than any other. To keep leakage close to zero, then, all the stovepipe joints were sealed with furnace cement and/or tape . . . and fastened with sheet metal screws.

The stoves were run for 8 to 14 hours per day. Each daily schedule included a hot fire-to simulate a homeowner's morning warm-up burn-and, typically, two or three lower-power, smoky fires . . . like the long-duration burns often used to maintain temperature all day and/or through the night. The combustion air inlets on the stoves were set to achieve the same burning conditions . . . so that the smoke density, composition, temperature, and velocity would be iden tical at the flue collar of each stove. We used the appearance of the fires, the surface temperatures of the stoves, and the temperature of the smoke just below the devices as indicators of uniformity.

Thermocouples were used to measure stove gas temperatures both below and above the devices (as shown in the accompanying diagram of the installation), and the temperatures were monitored constantly, using chart recorders. If the fires began to burn in a nonuniform fashion, the fuel loads were stirred, oroccasionally-the air inlets adjusted in order to bring them back in line. During the hot fires, temperatures at the lower thermocouple averaged 325 to 350°C (617 to 662°F) . . . while those recorded in the course of the cooler, smoky burns averaged 140 to 175°C (284 to 347°F) at the same location.

Both a hardwood and a softwood were used as fuel . . . with the moisture content ranging from 11 to 21%. But for any given fuel loading, wood of the same species and moisture content was used in all the stoves.

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