Anatomy Of Your Fireplace
In your masonry fireplace there is an area called the smoke chamber. In most fireplaces it can be easily viewed by shining a strong light up through the damper. Its function is to safely transition smoke and hot gases from your fireplace to the narrow flue of your chimney. Roughly the shape of an upside down funnel, the smoke chamber starts just above the damper and ends where the chimney begins. The bricks along the sides of the smoke chamber are often stepped outward one above the other until they meet the flue. This is a process called “corbelling”. The corbelled brick in your chamber will look like an upside down staircase. To protect the integrity and efficiency of your fireplace, the smoke chamber should be free of any gaps, cracks, or jagged edges. The corbelled areas of the smoke chamber should be coated with an insulating, high-temperature mortar to fill any gaps and smooth out any jagged edges.
Smoke Chamber Or Fire Chamber
According to the National Fire Protection Association (NFPA), defective smoke chamber are the third leading cause of chimney related fires. For the safety and efficiency of your fireplace, it is important that any gaps, cracks, or holes in the smoke chamber be sealed and the brick corbelling be made smooth. Because the smoke chamber is a “high heat” area, any gaps, cracks, or holes can allow excessive heat to attack any surrounding wood or combustibles. The jagged corbelling slows the draft and will provide more surface area for highly combustible creosote and soot to form.
Anatomy Of Your Chimney
Whether your chimney is used to vent a fireplace, woodstove, or furnace, most have sections of clay flye tile stacked one above the other to form a liner called the flue. The flue liner should be tightly sealed to protect the integrity and efficiency of your chimney. But over time, hidden dangers can develop that will compromise the safety and efficiency of your chimney.
Are There Hidden Dangers In Your Chimney?
Gaps Between Flue Tiles
The combustion process creates noxious gases that can contain creosote/soot, carbon monoxide, and corrosive chemicals. The purpose of your chimney is to safely vent hazardous flue gases from your home. Flue tiles are typically sealed with mortar to keep these gases within the flue. But over time, the mixture of heat, moisture, and chemicals will erode the mortar, leaving gaps or voids between flue tiles.
Cracked Flue Tiles
Flue tiles crack due to “sudden occurrences” such as chimney fire, lightning strike, or seismic event. Cracks may also be caused by poor workmanship or settling of your home.
Flaking Flue Tiles (Spalling)
Years of exposure to corrosive chemicals can attack clay flue tiles, causing pieces of the flue liner to flake off or delaminate, a process called spalling.
How These Hidden Dangers Can Affect You
Fire & Health Risks
These defects, no matter how small, begin a process that will further erode the chimney and can pose a threat to your family’s health. When heat, moisture, and gases escape through gaps or cracks in your chimney, they deteriorate your chimney from the inside out. More importantly, the gaps and cracks can cause health risks, by allowing poisonous gases to escape into your home. Combustible creosote or soot can escape through these openings and build up outside the flue liner. If the creosote were to catch fire in this area of your chimney, serious damage can occur, because the fire can no longer be contained within the flue. Pieces of flue tile that flake off due to spalling can form dangerous blockages within your chimney.
Loss Of Efficiency
To work correctly and efficiently, chimneys must be gas tight and free of gaps and cracks. Gases rising up through your chimney are similar to liquid being sipped through a straw. If the straw has a crack or hole in it, the liquid will not flow effectively through it. Gaps or cracks allow excess air into your chimney, slow the updraft and make it harder for smoke and gases to rise up and out. Hence, the fireplace, woodstove, or furnace will perform poorly, resulting in loss of heat efficiency.