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Up in Smoke

How can you tell if your chimney is a fire hazard? Follow the advice of chimney specialist Mark Shaub who checked out the chimneys on This Old House TV's Charlestown project

<p><em>This Old House</em> TV's Charlestown house project</p>

This Old House TV's Charlestown house project

When I first came to look at the chimneys on This Old House TV's Charlestown project, series producer Bruce Irving told me that there were four fireplaces with beautiful mantels, but was unsure of their condition. Little did Bruce or the homeowners know that these fireplaces were actually fire hazards.

Whenever I look at a job, I examine not only the chimney but the entire

chimney system. This means checking the distance between

combustibles—such as wood framing or mantels—and wood or coal stoves,

boilers furnaces, fireplaces and smoke pipes in addition to inspecting

the actual chimney for proper height, size, lining and clearance from

combustibles. I also check the sides, rear and underside of the firebox

as well as any hearth extensions for proper size and clearances. A

certified chimney professional should both clean and evaluate your whole

chimney system once a year. In most of the United States, no license or

certification is required, so homeowners should ask their sweep for an

up-to-date certificate from the Chimney Safety Institute of America,

which requires sweeps to pass a written examination based on fire codes,

clearances and standards for chimney construction and maintenance. In

addition you should call references and ask for proof that the chimney sweep is fully insured. Many municipalities

actually have codes that are more stringent than the national fire code,

so it is important that your sweep also have knowledge of local codes.

Today the predominant lining of masonry chimneys is terra cotta tile.

Prior to the 1920s, chimneys were typically unlined, consisting of brick

or stone and soft mortars, with their wood framing in direct contact

with the chimney. The most commonly burned fuel was coal, which created

an acid rich environment within the chimney that actually ate away at

the unprotected brick and mortar. This combination of acids, exposed

wood framing and lack of lining is recipe for a house fire. In

1994, 32,500 chimney fires in the United States resulted in 70 deaths,

and $181.8 million worth of damage. Virtually all of these fires were

preventable with proper yearly inspections.

Burning wood produces a sticky, tar-like flammable substance called creosote that can ignite and

send flames up the flue, raising temperatures as high as 2,300

degrees—hot enough to melt mortar, crack flue tiles and char or burn

nearby studs and rafters. Creosote comes in three different strengths:

first-degree creosote is a fluffy gray dust; second-degree is denser and

looks like blackened popcorn; and third degree creosote is crystallized

and hard like rock candy. Most chimney professionals now have a closed

circuit TV camera that can be inserted up the chimney for a closer look at

creosote buildup. Although this service costs a little more, it usually

reveals otherwise hidden problems and also allows homeowners a first-hand look at the culprit.

The four fireplaces in the Charlestown house figured prominently in the renovation plans. If they could get them working, the homeowners could add over $20,000 in value to their home. But this was not as

simple as it sounded. The chimneys were unlined,

originally used to feed hot air from the basement furnace into the rest

of the house. In the first floor dining room, the tiled hearth and gas

log were added around the turn of the century. In the second floor

dining room, the fireplace was gradually built up around an outlet for a

wood stove pipe. In the second floor living room, currently outfitted

with a gas-fired log, I found charred wood in the framing around the

chimney from the heat that the logs threw off. Because these fireplaces

weren't originally used for wood burning, they would be complicated—and

expensive—to get fired up. I recommended that the homeowners focus on

the two living room fireplaces: relining the chimneys, building masonry

fireboxes and moving the wood a safe distance from the hearths. All

this rehabilitation would cost nearly $20,000—the very cost they could

recoup whenever they sell the house. This news was more than they had

bargained for; most of the hazards were hidden within the walls behind

the decorative fireplaces they fell in love with. But these chimneys

were a classic case of what you see isn't always what you get.