TESTING CREOSOTE-REDUCING DEVICES: THE RESULTS

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Issue # 74 - March/April 1982

In the last issue of MOTHER we described a research project, which was then underway, that we hoped would allow us to evaluate the creosote-reducing effects of three add-on devices for woodstoves. In the ensuing two months we completed the testing, and can now report the outcome of our research.

The three pieces of equipment tested were a typical barometric draft control (made by Steinen of Carolina, Inc.), the Smoke Dragon catalytic afterburner, and the Smoke Consumer filter. For the sake of those readers who might have missed the first article, we'll begin by briefly describing the products and reviewing the testing procedures.

Barometric draft controls (see the accompanying photos for examples of all three tested products) are designed to prevent excess draft, and are usually installed in the stovepipe between the appliance and the chimney. The primary working part of such a device is a hinged and weighted flap that's closed when there's no fire in the stove. During operation, however, suction will pull the flap open when the draft exceeds a preselected value. This lets room air into the chimney, which prevents the draft from becoming greater than the chosen setting (adjustments can be made by moving the weight attached to the flap).

The Smoke Consumer consists of a knitted wire mesh filter attached beneath a cast-iron plate. The assembly can be rotated to lie either at a right angle to or parallel to the smoke flow . . . just as can a simple stovepipe damper. When the filter is closed (set across the flow), much of the flue gas moves through its passageways (a little smoke does flow around the device, in the space between the plate and the stovepipe wall). The manufacturer claims that the Consumer works by filtering out particles . . . consequently, the wire mesh requires periodic cleaning. Recommended maintenance includes a "continuous burn reactor cycle" once each daywhich involves running the stove hot enough to burn material off the filterand a weekly manual cleaning of the mesh.

The Smoke Dragon is a catalytic afterburner and heat exchanger that's designed to ignite smoke as it escapes from the stove. The catalytic combustorwhich is manufactured by Corning Glass Works-is a ceramic honeycomb structure, about six inches in diameter and three inches long, coated with a very thin layer of a noble-metal catalyst (such as platinum and/or palladium).

Essentially, the catalyst lowers the ignition temperature of the smoke from around 600°C (1,112°F) to roughly 260°C (500°F). Thus, if the gas is hot enough, and if it contains adequate oxygen, much of the escaping material will be burned in and just above the catalyst. Furthermore, once the Dragon begins working, it will continue to burn some gas even if the smoke temperature entering the device falls somewhat . . . because the heat generated by the burning smoke in the combustor warms the incoming fumes enough so that they, too, will ignite.