The Internal Structure of a Brick Fireplace

Foundation

• Just as the foundation of a home is important, so is the foundation for a fireplace. A properly installed fireplace will have a foundation -- or footing as it is called in some areas -- that is separate from that of the home.

Inner Hearth

• The area directly underneath the fire is called the "inner hearth" and serves as the floor of the firebox, extending from inside the firebox into the room. The hearth areas that are inside of the room are referred to as the "outer hearth." The floor of the inner hearth is where ashes are deposited from burning logs and should be routinely swept free of ashes once the ashes are no longer hot and embers have died.

Butt Walls

• The butt walls form the perimeter of the fireplace and enclose the firebox, starting at the base of the foundation and rising to the bottom of the flue at the point where the chimney structure begins. Fireplace inserts and zero clearance units (prefabricated fireplace installed right against the butt walls) are installed to fit right up against the butt walls.

The Firebox

• The fireplace sidewalls that line the inside of the fireplace form the "firebox," which is where you build the fire with logs. Inserts and zero clearance units serve as the firebox in homes where they are installed. In older homes with all-brick fireplaces, the section of the butt walls that is visible from inside of the room serves as the firebox area. The firebox -- whether it is an insert or butt walls -- must be properly sized and sloped so that the heat from the fire is emitted into the room.

Smoke Shelf

• Air from the outdoors can create a downdraft inside of the chimney. The job of the smoke shelf is to redirect any downdrafts back up the flue so they exit the chimney. The smoke shelf has a curved upper surface to redirect smoke and extrudes from the rear of the butt walls, located behind the damper and the firebox.

Damper

• The damper is a plate or valve that regulates air drafts when the flue is closed. It is manually operated and should be fully open before you light a fire, which is usually done by turning the damper knob. The damper is opened to ensure that smoke rises up the chimney instead of into the room and directs the heat to flow inside of the room from the firebox.

Flue

• The flue is the passageway of the chimney. The function of the flue is to actually create a current and draft so that the smoke will rise up the chimney and exit to the outdoors. Flues begin and extend vertically from the smoke chamber to the top of the chimney. When chimneys are inspected, the flue is checked to ensure it does not have any leaks and is operating properly.

Chimney

• Next to the fireplace and hearth, the chimney is probably the part of the fireplace that is recognized the best, but many people aren't exactly sure where the chimney starts. The vertical area that begins right after the smoke chamber is when the chimney "officially" becomes the chimney. The chimney is comprised of the masonry walls that surround the flue, the flue liner, flashings and other mechanics that are essential to making a fireplace perform properly.