HOME MAINTENANCE : It’s Flue Season: Where There’s Smoke, There’s a Problem : Keep Fireplace Trouble-Free and Don’t Get Burned

It’s cold--outside and in.

So you dump a handful of kindling on the grate, open the damper, add an armload of split logs, turn on the gas, light a match and smell smoke.

Wait a minute. Smell smoke?

That’s not supposed to happen. The damper is open, remember?

What you’ve got is a fireplace problem.

But long before you get to this point--the point where you need to hire someone to tell you whether it’s a big, expensive problem or a little, less costly one--there are things you can do to keep trouble from developing. Fireplaces, after all, aren’t that complicated.

Barring a natural disaster (spell that e-a-r-t-h-q-u-a-k-e) that causes the mortar to crack and masonry to fall, a fireplace really is one of those things that, with a little preventive maintenance and a lot of common sense, can practically run forever.

So before you light your next fire, take a moment to consider this advice from fireplace expert Jeffrey Cullen, owner of A-1 Chimney Sweeps in Costa Mesa.

Most fireplace problems, he says, come from not taking care of the chimney liner--called a flue--and the external metal parts that a fireplace uses: the damper door and its handle and hinges; the fireplace screen and its mount, and the chimney spark arrestor and cap that all wood-burning fireplaces should have--and that 70% don’t.

“If it was built right in the first place,” Cullen says, “there’s not much that can go wrong with a fireplace without human help.”

The most common problems in Orange County, he said, are creosote deposits, which spew toxic chemicals into the air and can cause disastrous chimney fires; smoke and fumes inside the house, caused by wind blowing down an uncapped chimney; and water damage to masonry or metal parts caused both by rain that enters an uncapped chimney and the vapor released from burning logs (yes, burning logs--a hunk of firewood, even well-dried, contains up to 50% water).

The first and most common problem is creosote--a black or dark brown deposit that collects on the inside of the chimney, the smoke chamber and the back of the metal damper.

Creosote is formed as gasses in the wood smoke condense on the cool surfaces inside a fireplace. The gasses contain more than two dozen toxic compounds and, in solidified form, are highly flammable. Creosote can be a thin, runny fluid but generally is deposited inside a chimney either as a sooty substance that looks a bit like fine coffee grounds or as a thick, dark tar-like substance.

To minimize creosote build-up, Cullen says:

* Burn only seasoned (dried) hardwoods, such as oak or eucalyptus, which burn hotter and emit less smoke than soft woods such as pine;

* Don’t allow a fire to smolder overnight in the firebox--the part of the fireplace where logs are burned--because that keeps creosote-causing smoke inside the chimney longer;

* Don’t burn paper or trash in the fireplace; this creates more smoke than does wood;

* Check your fireplace annually for creosote and clean it--or hire a sweep to do the job--when the creosote gets to be more than a 1/4-inch thick ( 1/8-inch in a factory-built metal fireplace chimney).

Checking for creosote, if you do it yourself, involves opening the damper (the metal flap that lets air flow out of the firebox through the chimney) and shining a strong light into the smoke chamber, which is directly above the firebox. Use a long screwdriver or other piece of metal and scratch the creosote that lines the chamber, then estimate the depth of the scratch.

The cost of a professional chimney sweep varies, but the range for most two-story homes is $80 to $100 ($60 to $80 for one-story homes) unless there are multiple chimneys, other problems that must be fixed or unless you wait until the creosote is so thick there is a lot of extra labor involved in its removal.

Downdrafts--air flowing back down a chimney--are almost always caused by ill-fitting dampers and the lack of a chimney cap (or an improperly installed cap).

“A chimney is nothing more than a hole in your house,” Cullen says, and although the damper is supposed to help keep it sealed when there’s no fire, very few original equipment dampers in masonry fireplaces are air tight.

Another damper-related problem that occurs all winter in masonry fireplaces--and some metal models--is the escape up the chimney of up to 40% of the heat from your home furnace.

Fireplace specialists claim that installation of a chimney top damper in a masonry fireplace can result in a dramatic savings on home heating bills. The dampers are stainless steel doors that operate from inside the house like a normal damper but that seal the entire chimney so no air escapes.

Without a positive seal, high winds such as the Santa Anas that bedevil Orange County for most of the fall and early winter can set up a tremendous downdraft in an unprotected chimney. The wind blowing down the chimney can force soot and creosote fumes into the interior of the house around a loose or ill-fitting damper when it is closed and can push smoke and sparks back down the chimney when a fire is going and the damper is open.

The cure is a metal or masonry cap fastened over the chimney opening to let smoke out and keep most winds from entering

Metal caps, generally incorporating a wire spark arrestor in their design, can be obtained at fireplace supply stores, home and building material stores or through a fireplace cleaning professional. Masonry caps, which are more decorative and more expensive, generally must be purchased from a fireplace or masonry professional who can install them properly.

Chimney caps also keep leaves and debris out of the chimney and prevent birds and small animals from entering the house through the chimney. And they help minimize water problems in a fireplace by keeping out rain.

Water combines with creosote inside a fireplace to form a particularly corrosive acid that runs down the back of the firebox and eats away at the mortar fastening the bricks lining the back wall. The resulting cracks and fissures can be a fire danger if they channel flames or heat from the fire to flammable parts of the home’s framing.

In all-metal fireplaces, acid and rust from rainwater can eat holes in the firebox and chimney, requiring costly replacements.

Water in a fireplace--from rain or from vapor trapped in the burning wood--can also cause rust damage to moving metal parts such as the damper and its hinges, the mechanism that operates the fireplace screen and even the metal gas pipe in a gas-fueled fireplace.

To reduce rust, Cullen recommends spraying all metal parts with a penetrating oil, such as WD-40, at the beginning of each fire season--more often if you are a “heavy burner” and use your fireplace frequently.

To get the most benefit from a fire, Cullen recommends placing the grate that holds the wood as close to the rear of the firebox as possible. The back wall of the fireplace “is where all the drafting that makes a fire burn well takes place,” he said. A fire well-fed with oxygen carried in the draft of air pulled from the floor of the room into the firebox and up the chimney is a fire that burns hotter and cleaner.

Cullen offers one more tip for homeowners with masonry fireplaces--consider using a metal fire reflector placed against the back wall of the firebox.

Most modern reflectors are made of stainless steel and radiate heat from the fire into the room. Also available are thick cast-iron plates, which in addition to bouncing heat into the room while the fire is burning, actually soak heat from the fire and radiate it into the room after the flames have died.

With stainless or cast iron, less of a fire’s heat goes up the chimney, less is absorbed by the firebox walls to damage the masonry and more is cast out in to the room.

By keeping a clean fireplace that is in good repair, Cullen says, the fires you burn not only are more visually appealing, they generate more heat and are more physically comforting.

And that, in most homes, is what a fireplace is all about.

Chimney Cross-section

Chimney cap

Spark arrestor

Flue: Chimney passage allowing smoke and gases to escape.

Smoke Shelf: Shelf or depression located in back of the damper to prevent downdrafts from blowing smoke into the room and collect debris falling down the chimney.

Damper: Metal trap door used to control the draft of a fire.

Firebox: The chamber of a stove or fireplace where the fire burns. Lined with special fire bricks in masonry fireplaces.

Ash pit door

Ash pit (optional)