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Provided by: Lee Masonry Products, LLC
Provided by: Lee Masonry Products, LLC
An Information Series © National Concrete Masonry Association
3-7A: CONCRETE MASONRY FIREPLACES
The chimney must extend at least 3 ft (914 mm) above the point where the chimney passes through the
roof and at least 2 ft (610 mm) above any part of the building within 10 ft (3,048 mm) of the chimney (see
Figure 2). Higher chimneys may be required for adequate draft. Good draft is normally achieved with 15 ft
(4,572 mm) high chimneys (measured from the top of the fireplace opening to the top of the chimney).
The chimney must be capped to resist water penetration. A mortar wash that is feathered to the edge of
the chimney wall is not an adequate cap. The cap should be either cast-in-place or precast concrete, as shown
in Figure 2. Metal pan flashing over the top of the chimney will also perform adequately.
ENERGY EFFICIENCY
Proper fireplace design and operation helps maximize the efficiency. Maintaining efficient fuel
consumption by properly adjusting the damper is critical. There are several other ways to significantly improve
the performance of the concrete masonry fireplace. For example, positioning the fireplace on interior rather
than exterior walls reduces heat loss when the fireplace is not in operation, and increases the amount of
usable radiant heat from the concrete masonry.
Fireplace efficiency can also be improved by introducing external air into the firebox for draft and
combustion (not within the garage or basement. An external combustion air system requires a damper in the
firebox, adequate ducting or air passageways and a grill or louver at the exterior opening. The external air
damper should permit the control of both the direction and volume of the airflow for temperature control. The
damper should be capable of directing air flow towards the back of the firebox so that when down drafts or
negative pressures occur, hot ashes or embers are not forced into the room.