Version 1.04
March 2011
APEX cbt
Page 17
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THIMBLE
A thimble must be used when the connection from the furnace is made
through a combustible wall to a masonry chimney. There are several
methods to use for connection through a combustible wall, two of which
are illustrated in this manual. Local building authorities may be consulted
or NFPA 211 may be used for additional methods of chimney
connection.
Also, listed prefabricated metal thimbles may be purchased for use with
wood furnaces. The manufacturer's installation instructions for the
thimbles must be strictly followed to assure the safety of the system. Be
sure to maintain the designated clearance to combustible materials.
BRICK CHIMNEY THIMBLE ASSEMBLY
Construction of the brick thimble assembly requires 12 inches of brick around a fire clay liner. Be sure the
point of penetration allows an 18 inch clearance from the
connector to the ceiling. An appropriate opening for a chimney
connector must be cut in the wall to maintain the required 12
inches of brick separation from combustibles. It will be
necessary to cut wall studs and install a header and sill frame to
maintain proper dimensions and to hold the weight of the brick
(Fig. 13). NOTE: Whenever cutting through a wall, check first
with local building authorities to be sure building integrity is
maintained. Minimum 3 1/2-inch (4-inch nominal) thick solid
bricks are to be used. The fire clay liner (ASTM C35 or
equivalent), minimum
5/8 inch
wall thickness,
must not
penetrate into the chimney beyond the inner surface of the
chimney flue liner and must be firmly cemented in place. If it is
necessary to cut a hole in the chimney liner, use extreme care to
keep it from shattering. Refractory mortar must be used at the
junction to the chimney liner (Fig. 14). After the assembly is
complete, insert the chimney connector in the fire clay liner. Do
not push it beyond the inside edge of the chimney liner because
this will affect the draw of the chimney.
Fig. 11 Clearances—Masonry To Combustibles
Fig. 12 Minimum Chimney Height
12"
Fig. 13 Brick Chimney Thimble
INSTALLATION INSTRUCTIONS - VENTING
