Stop a chimney backdraft caused by wind by installing a baffled chimney cap on the unit. These devices reduce the amount of wind that blows back down the flue through the fireplace or wood stove and prevent smoke and toxic gases from drafting back into the house while still providing openings that allow the smoke to exit the top of the stack. Chimney caps are available for both manufactured and masonry chimneys.
Under normal circumstances the chimney draws air from the firebox because heated air is less dense than cool air. The air the fire warms rises and exits the chimney, pulling the smoke and other fumes from the fire. However, an running exhaust fan sometimes overpowers the natural draft of the chimney, pulling the odors back into the home. When burning a fire, minimize the use of bathroom and cooking exhaust fans to prevent backdrafting. Open a window to neutralize the pressure differential if vent use is essential.
When starting a fire, the initial temperature differential may be insufficient to cause the smoke to rise. Beginning the fire with paper and fast-burning kindling warms the chimney and starts the air moving in the correct direction.
Chimneys also build up creosote with use. This byproduct of burning can cause a blockage of the chimney so it does not exhaust smoke. Hire a chimney sweep to clean the flue to eliminate backdrafts due to a blocked chimney.