Problem Solving for Smoky Fireplaces Article

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• Optimum Chimney Height

• Fireplace Opening & Flue Sizes

• Getting Enough Air

• Obstructions

• Occasional Problems

• Just Can't Wait?

Far and away the most common complaint with fireplaces is smoking. Usually the smoking can be categorized as preexisting, new, or intermittent. Although smoking can be caused by a variety of reasons, you can generally figure out the problem with just a little detective work, starting with the chimney.

Chimneys are actually quite simple in theory. A chimney is just a column of air that, being warmer than the air above it, tends to rise and draw air (or a fire's smoke) in at the bottom to replace the air going out the top.

Optimum Chimney Height

Preexisting conditions usually are caused by not following the basic rules of chimney construction. A chimney should project at least 3 feet above any point within 10 feet of the chimney. To take an extreme case as an example, if a chimney on a one story addition is within 10 feet of the three story main house, your chimney would have to be at least 18 feet above the one story roof (8 feet for each of the two higher stories plus 2 feet). The taller the chimney, the stronger the draft. Sometimes a short chimney may not have enough draft even though it follows the 3-2-10 rule, but the addition of a few feet will solve a smoking problem.

Fireplace Opening & Flue Sizes

For a fireplace that always smokes, the first thing to check is the relationship between the area of the fireplace opening and the area of the flue. The opening should be no more than 10 times the area of the flue. For example, a 33"W x 29"H opening is 957 sq. in. A 10" x 10" flue would be large enough at 100 sq. in., but an 8" x 10" flue would be too small at 800 sq. in. To test whether decreasing the opening size would eliminate the smoking problem you can use a piece of sheet metal or a row of bricks to reduce the opening.

Getting Enough Air

An extremely airtight house can also cause a smoking fireplace. Newer houses, particularly, often will not let in enough air to replace the air drawn out by the chimney. Open a window or door close to the fireplace to see if this stops the smoking. If it does, add a vent to bring combustion air to the fireplace or leave a door or window cracked while burning. Many new houses have fireplace vents built in. Look in or near the fireplace to see if there is a closed air inlet vent in yours.

Obstructions

New smoking problems with a fireplace that previously drew fine are easy to trace. Look for obstructions at the top of the chimney. A cap may have a clogged screen, or trees may now be blocking the exit. If you have not had your chimney swept recently, a buildup of creosote could be the culprit.

Birds, squirrels, raccoons, or other animals can also block a chimney. Often you will hear them in the chimney, but the best solution is to install a chimney cap to avoid the problem before it happens. A cap also protects your chimney from deteriorating in the weather.

If critters have already moved into your chimney, seek removal assistance from someone trained in the area, as bites, rabies and other problems can result from attempting to do this work yourself (see Nuisance Wildlife Removal in the yellow pages of your phone book).

Occasional Problems

Intermittent smoking problems are often the hardest to trace, but here are some things to look for. If your house is moderately airtight, other appliances can draw enough air to cause the fireplace to smoke. Running kitchen or bathroom exhaust fans, or a furnace coming on can create the negative pressure needed to pull smoke from a fireplace. As with airtight homes, you will need to get more air to the fireplace either by cracking a window or door, or adding a fireplace vent.

Sometimes smoking can be cause by wind overcoming the draft and pushing smoke down the chimney. The siting of a house in relation to a hill, other buildings, or trees can cause wind to veer down a chimney. Short of cutting down trees or moving the house, you can try one of the chimney caps specially designed to protect against downdrafts.

Just Can't Wait?

Finally, intermittent smoking can be caused by an overeagerness to have a fire. If the temperature difference between the air in the chimney and the air outside is not enough, the chimney will be slow to draw. The solution? Try holding a piece of lit newspaper up the chimney to help warm the air column.

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