HIGH STAKE SWEEPS

Image Gallery A sweep empties creosote and soot from a stovepipe. The wire brush (foreground) is used for chimney cleaning

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From the Canadian magazine Harrowsmith comes this helpful excerpt on how to sweep your own chimney.

Reprinted by permission from Harrowsmith Magazine, copyright© 1980

By Matthew Radz

Whether cleaning one's own chimney or relying on the services of a sweep, the burner of wood should be aware of what is being removed and why it cannot be allowed to accumulate in a flue.

Creosote is the bane of many contemporary wood heating systems, and it is produced in quantity by a slow-burning, smoldering fire . . . the very sort that makes for those 6- to 16-hour burns of which many stove owners are so proud.

Creosote is the name of a specific chemical compound (C 8 H 10 O 2 ), which, in its commercially available form, is used to weatherproof railroad ties and other wood. It also occurs in chimneys used to vent wood smoke, but creosote from a sweep's viewpoint is a complex mixture of wood tar, soot, and other by-products produced by the burning of wood.

It appears in three primary forms: a thin, watery fluid that consists of creosote and soot mixed with water which has condensed in the chimney . . . a dry, black, gray, or brownish brittle crust found clinging to the inside of the flue . . . and a tarlike, sticky layer which can seriously clog a chimney. The sooty fluids and the tarlike layer are practically impossible to remove before they become pyrolized. These forms of creosote ignite only at extremely high temperatures. It is the brittle, pyrolized creosote which is the potential fuel for a flue fire.

Although relatively little research has been done on creosote formation, it is believed that three main factors determine the amount that is deposited at a given time or in a given chimney.

[1] Smoke Density. Creosote builds up when thick smoke, sometimes known as tar fog , condenses on the walls of a cool flue. Dense smoke occurs when a fire is oxygen-starved or when green wood is burned.

Contrary to the popular notion that seasoned hardwood will not yield creosote, there is ample evidence to show that even the driest, hardest of woods can cause problems if improperly burned. An airtight stove kept constantly in a tightly dampered state burns wood very slowly, producing heavy smoke and large amounts of incompletely burned wastes . . . no matter what fuel is used.

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