Beverley Square West Association

Chimney Maintenance from NY Times

Keeping a Chimney Free From Problems By JAY ROMANO

Published: December 19, 2004

WHILE the basic strategy for venting exhaust gases from a furnace or a fireplace seems pretty simple - send them up a chimney - chimneys are not necessarily simple things. In fact, chimney-safety specialists say, more can go wrong with a chimney than most people think.

"When fuel prices are elevated, you see greater use of wood stoves," said Ashley Eldridge, director of education for the Chimney Safety Institute of America, in Plainfield, Ind. "But you can have problems with your chimney even if you're not burning wood."

Mr. Eldridge explained that chimney problems fall into several categories. Chimneys - which contain one or more passageways called flues - can be fully or partly blocked; their interiors can be deteriorated or damaged to the point where dangerous gases can seep into the living area; they can be too big or too small for the appliances they are venting; they can be natural laboratories that produce mortar- and metal-corroding acid; and they can even be fire hazards themselves.

"Chimneys can be blocked by squirrels, birds, mice, leaves and twigs," Mr. Eldridge said, adding that even if a chimney is not fully obstructed, the reduction in its ability to vent gases could create a hazard. "The blockage could create pressure in the chimney that pushes dangerous gases back into the home."

The best way to avoid blockage, Mr. Eldridge said, is to install a rain cap - for about $100 - that allows smoke out while preventing animals and debris from getting in. Installing a cap eliminates another major chimney antagonist: water.

"If people don't have a rain cap, water runs down the inside of the chimney liner, it becomes acidic, and then the acid eats away at metal components like the chimney damper," Mr. Eldridge said.

Another problem can occur when people make more use of their chimney than it was designed for.

"If you use an ordinary fireplace as the primary heat source, you could be stressing the limits of the chimney," Mr. Eldridge said, explaining that a chimney designed for only occasional use might not be up to running nonstop for days. "The chimney can become saturated with heat and then transfer that heat to any combustible material it comes in contact with."

And while the result of having a chimney too small for the fire it is venting is fairly obvious - smoke that can't get out the chimney gets into the house - it is also possible to have a chimney too big for the job.

Flues in chimneys designed to vent an open fireplace, for example, will probably be too large to efficiently vent exhaust gases from wood stoves. "If the flue is larger than needed, the smoke tends to hang around inside the chimney and the chimney itself tends to be cooler than it should be," Mr. Eldridge said. "And that sets the stage for the deposit of creosote on the chimney walls." Creosote, he said, is basically unburned wood that sticks to the walls. When enough is present, the chimney itself can catch fire, using the creosote as fuel.

Finally, Mr. Eldridge said, a common and insidious problem is a deteriorating chimney liner. Chimney flues, he said, are typically lined with clay sections joined with mortar. When condensation from combustion comes into contact with the chimney liner, the acidic moisture eats away at the mortar. "The chimney can literally self-destruct," he said.

He said that homeowners who use their fireplace or wood-burning stove more than occasionally should have their chimney inspected at least once a year and cleaned when necessary. An inspection and a cleaning cost about $100 each, perhaps somewhat less if combined. A list of inspectors certified by the Chimney Safety Institute of America can be found on its Web site, www.csia.org.