Dirty chimney can be a house's deadliest enemy


October 13, 1990|By Carleton Jones

A few years back on a nippy fall day, I was asked to tend the fire in the old country home of a relative . . . just toss logs into the old Gothic-style woodstove that heated the downstairs living room.

I duly did the job -- and overdid it.

A few minutes after I rammed the dry logs into the firebox I heard an odd, whistling noise. Soon it rose to a jet plane-type roar.

The racket brought everybody to the first floor on the run, since we were many miles from a fire department. What had happened was the ignition of creosote in the chimney. Walls near the old flue for three floors up warmed up almost too hot to touch. There was a wild move to take to the roof and pour water down the shaft, but this was avoided. Fortunately and gradually, the roaring, burning flue cooled; the sparks and flying embers it sent all over the dry, outdoor wood lot burned out.

A lesson was learned. Chimneys, it seems, can be the most dangerous thing in your house.

L That's because so few people ever see that they are cleaned.

"Creosote will ignite at 451 degrees, about the same ignition rate as ordinary paper. It can turn anybody's chimney into an inferno of 2,100 degrees within seconds," says Jack Gray, a chimney pro and operator of Ye Olde Chimney Sweeps of Annapolis. (The firm has worked on flues in the historic Peggy Stewart house, Annapolis).

Twelve years of climbing roofs and scouring flues have made Mr. Gray wary of consumer indifference to their fireplace hazards. "A chimney fire in an older house can transfer to the wood structure and result in a disaster," says Mr. Gray. He adds that home flues equipped with woodburning stoves especially should be inspected once a year.

It's not only wood-burning fireplace chimneys, however, that are risky. Dangerous deposits can and will build up in any flue, even those venting coal, oil or gas furnaces.

Right now, the safest liners for chimneys appear to be made of stainless steel, Jack Gray says. Installations generally will run from $1,500 to $3,000 per job, but in place the metal will greatly outlast fire brick or ceramic tile. The round steel liners are said to draw more rapidly and eliminate poisonous vapors more efficiently than traditional masonry work. To prevent the spread of heat into home timbers or walls, areas between the liners and the chimney's inner walls are insulated to keep the heat of the metal under control.

In older neighborhoods where, some time in the past, oil-heat fumes were vented, heavy sulphur deposits result. If, at some later time, a homeowner converts his chimney to high-efficiency gas furnaces, the heavy moisture from these systems will form sulfuric acid. Clay chimney linings disintegrate under the assault of the acid and collapse on themselves. This could further block a flue and force deadly carbon monoxide into the home through cracks or out a fireplace or fire box.

A New Jersey utility was forced to start mass inspections of flues to whip such a carbon monoxide and sulphur problem. "It's an indication that chimney sweeps do not just serve the woodburning customer. Other heat sources can be dangerous if not professionally watched," says John Bittner, executive director of the 900-member National Chimney Sweeps Guild.

Chimney conditions are often overlooked in otherwise complex realty contracts and sometimes skipped over by professional engineering inspections.

Guild members estimate that less than 20 percent of American )) homeowners realize chimney hazards and the necessity of regular inspections, Mr. Bittner reports. The guild goal is to persuade the public to develop regular schedules of home-heating maintenance that will keep structures safe.

Many Maryland area homes are at risk of more than chimney fires from creosote. Perhaps the most lurid combination is venting all the heat and home energy pollution in one flue -- say connecting in one chimney drafts from a furnace, a woodstove and a fireplace in the same dwelling unit.

"This is in direct violation of the National Housing Code," says Jack Gray.

The code of the National Fire Protection Association bans the blending of home furnace gases and fireplace combustion in one flue and also outlaws the blending of solid-fuel drafts like those from coal, wood, pellets or corn in any flue that serves an appliance burning other kinds of fuel.

Very often, a simple cleaning of a chimney will be necessary before a good, long-range inspection to root out problems can be carried out, Mr. Bittner reports. The goal is to establish relationships with chimney sweeps so that they become part of a home maintenance team, the trade group director says.

Ideally, sweeps clean the system and then talk to the homeowner to determine the homeowner's habits regarding stoves and fireplaces. Based on that interview, the sweep should recommend a schedule of maintenance that will keep the home safe. The average cost of a simple cleaning and inspection in

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