Testing Creosote-Removing Devices

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Another technique that's commonly suggested for controlling creosote is to burn an intentional short, hot fire every day or two. The result of such a practice is either a small (and therefore supposedly relatively safe) chimney fire, or—more often—a drying and flaking of the thin tarlike layer . . . with the particles either falling or being blown out the flue. However, it's vital that there be only very thin creosote deposits present when this procedure is used, and only frequent inspections can establish that fact.

If the chimney hasn't been checked or cleaned for along time—or if the stove has been run at low power for a few days and a thick, tarry, highly flammable deposit has built up—an intentional hot burn could trigger a serious chimney fire. (You should, of course, avoid the technique if you have any doubts about the safety of the chimney itself.) In summation, then, though the hot fire method can work, the numerous "ifs" involved prohibit us from recommending it.

But what can be done to prevent, or at least minimize, creosote buildup in the first place? Two major factors affect the rate at which the substance collects, and solutions to the problem are most likely to be found by dealing with one or both of them: [1] the density of the smoke going up the chimney (that is, the amount of unburned material that remains in the gases) . . . [2] the temperature of the flue wall (cool walls increase the condensation and accumulation of creosote).

Flue wall temperatures are affected by the type of chimney used and by its location. Both double-wall/packed-insulation and triple-wall/air-insulation prefabricated chimneys do a better job of holding flue gas heat than do either masonry or triple-wall/thermosiphon (aircooled) types. And any of them will prove more satisfactory if located inside the house, where the exterior is in contact with warmer air than would be the case if the chimney ran up the outside of the dwelling. Long runs of stovepipe between the appliance and the chimney al so decrease flue gas temperature, and—therefore—increase creosote accumulation. In fact, the more heat is pulled out of the fire and flue gases—whether in the stove, in a heat exchanger accessory, in the stovepipe connector, or in the chimney—the cooler the smoke will be and the more the creosote will build up. Thus there's often a conflict between improving energy efficiency and minimizing creosote.

Stove operation, rather than design, is the single most important factor affecting smoke density in traditional woodstoves. As discussed in the last issue of this magazine (see "Woodstove Smoke" on page 72 of MOTHER NO. 72), you can limit creosote buildup by simply burning only small, hot fires in your stove.

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