Chimney Cleaning Revisited

Reprinted from Hart & Cooley’s “Tech Talk” May 2006 issue

It probably strikes you that this is an odd time of the year to be hearing about cleaning chimneys. Yet, cleaning a chimney in the spring, at the end of the heating season, is one of the most important elements of properly maintaining a chimney system. We want folks who have installed our chimney to enjoy the value of their investment by having the satisfaction that, with proper care, the chimney will have a long, safe life.

All fuels have some contaminants in them. Some, like coal, contain more than others. Burning trash, workshop scraps, and other burnable matter that cannot be classified as purely a “fuel” can contain very harmful chemicals. These chemicals may end up on the chimney walls as part of the creosote, soot, ash or debris that builds up over time when burning any fuel.

Most people realize that creosote buildup in a chimney needs to be addressed on a regular basis. But, as one’s train of thought frequently goes: “There isn’t enough junk on my chimney wall to be dangerous, so I’ll clean it later.” Just because the condensed material on a chimney flue may not be creosote, which can build up thick enough to start choking off the flow of gases, doesn’t mean it isn’t harmful, if not dangerous. Creosote can be highly flammable and, if ignited, can create a severe chimney fire - that’s dangerous! Soot, on the other hand, is not normally thought of as “dangerous,” nor does it build up layers thick enough to affect the draft. It’s only thought of as annoying, if it is thought about at all. But left alone, soot containing harmful acidic compounds can harm the chimney. Oil and coal fuels contain sulfur. When burned, the sulfur becomes sulfites and sulfates that end up being carried out in the flue gases. If these compounds trapped in the soot are allowed to sit in the chimney for long period of times, say all summer, the moisture in the air will combine with the sulfur compounds to form acids. These acids then begin to eat away at the stainless steel.

We ask that chimneys be cleaned at the end of the heating season to minimize the possibility of harmful residue remaining on the chimney wall during the off season. The sooner the can chimney is cleaned after the last use of the appliance the better. Thoroughly brushing the chimney is usually adequate to mechanically remove any build up of soot or creosote from the interior of the chimney for intermittent cleaning during the heating season. We recommend a final pass down the chimney be made with a brush wrapped in a rag. At the end of the season, spray the rag-wrapped brush with WD-40 for the very last pass down and back up the chimney. This will help remove all residual soot from the surface and leave a protective film on the interior throughout the summer.