What to look for
1. Examine the back of the firebox. A properly operating fireplace should have a hot white spot in the bottom center of the firebox.
2. If there are scattered white spots of soot on the lintel in front of the fireplace, there’s a draft issue that could be caused either by a chimney that’s too short, or by a chimney whose draft is being obstructed somehow.
a. If the chimney is too short, a mason can extend the chimney, though that is a more expensive fix. A cheaper, but temporary fix for this problem would be to crack open a nearby window whenever the fireplace is in use to assist the updraft.
b. If there’s an obstruction, either a chimney sweep or a landscaper/arborist can remove it, depending what and where the obstruction is.
3. Check the chimney for creosote. It’s a shiny, black, tar-like substance that forms when pine is burned in the fireplace and can cause destructive chimney fires.
a. A chimney sweep can come and clean the firebox and flue to remove any creosote.
b. A creosote cleaning log can also be burned to loosen up the creosote, though Mark recommends still hiring a chimney sweep since they can also examine the fireplace for any other potential fireplace hazards.
4. Assess the condition of the flue. Only in rare circumstances does the chimney need to be relined, since code requires all masonry in a chimney to be very thick to prevent stray sparks from causing house fires.
Pro Tip: Mark Schaub, owner of Chimney Savers in Hillsborough, New Jersey and a frequent flue-fixer for This Old House, says that diagnosing a smoking fireplace requires detective work: “To figure out why a fireplace smokes, you have to think like Sherlock Holmes.” He advises looking for clues not only in the way the chimney is built but also in the profile of the surrounding terrain, the height of nearby structures, and the weather conditions when the fireplace misbehaves.
Resources
Besides discussing the general operation of a fireplace, Mark also mentioned burning creosote cleaning logs, which can be found at any home center.
The National Fire Protection Association recommends that chimneys be swept at least once a year at the beginning of winter to remove soot and debris. In addition to cleaning, a chimney sweep should inspect the chimney structure for cracks, loose bricks, or missing mortar, and chimney liners should be checked for cracking or deterioration. You can find a certified sweep in your area at the Chimney Safety Institute of America’s website, csia.org.
Pro Tip: While cleaning logs may help with minor buildup, the only practical way to eliminate creosote is to brush it out. A professional chimney sweep seals the fireplace opening with a cloth tarp and inserts a vacuum hose to prevent soot from entering the living room. Working from the roof, the sweep pushes, pulls, and twists a brush sized to the flue down the chimney, adding 4-foot fiberglass pole segments as needed. In most cases, a two-man crew can complete the job within 45 minutes—though severe third-degree creosote may require three hours to remove with chains and drills.
