How to Fix Backdraft in a Chimney

Obstructions

• A chimney must have good air circulation at its opening to function properly. Some backdrafts result from external obstructions blocking or interfering with air movement around the chimney. A large tree near the chimney, for example, might result in poor air circulation and a resulting backdraft. Also, nearby buildings might interfere with air flow in the chimney's vicinity. Extending the height of the chimney top can often solve the problem, as taller chimneys draft more efficiently than shorter ones.

Negative Pressure

• A house develops negative pressure when more air is sucked out of the house than comes into the house. Negative pressure, one of the primary causes of backdrafts, often occurs when certain appliances, such as kitchen or bathroom exhaust fans, draw air from the home. Avoid running any exhaust fans when you have a wood fire burning. You might also relieve the negative pressure by opening a window to let in more air.

Starting Fire

• Fireplaces and chimneys operate on the principle that hot air rises. The heat produced by them creates an updraft that draws the smoke through the chimney and out of the house. When you first light a wood fire, it might not create enough heat to start an updraft immediately, allowing a backdraft to occur. Using newspaper or extra kindling to create a hotter blaze when the fire first ignites can solve the problem, according to the magazine "Extreme How-To."

Caps

• A strong wind may interfere with the chimney's ability to retain an effective updraft. The design of the chimney cap may also cause drafting problems. Special types of chimney caps, however, can take advantage of the wind to eliminate backdraft. These caps consist of two hoods positioned to guide the wind around the unit. As the wind goes around the cap, it creates an updraft, drawing smoke and gases from the chimney.