35
DM Chimney System: Offset Block (cont.)
With straight chimneys the front of the DM outer
casing block sits approximately three and three-quarters inch
(3- 3/4”) back from the front of the smoke dome. This allows
for a nominal 4” thick wall to be ush with the room side face
of smoke dome assembly while the DM chimney passes up the
backside of the wall.
For a nominal 2” by 6” wall thickness the chimney can
be offset 3” rearward. Set the rst DM outer casing block ush
to the back end of this offset block. This will leave a distance of
6-3/4” from the face of the rebox smoke dome assembly to the
face of the DM outer casing block. This allows for the smoke
dome to sit ush with the inside face of the 2” by 6” wall and the
straight chimney to run up the outside of the wall. (Figure 55).
For a wall thickness of 9”, nominal 8” CMU plus 1-1/2”
furring strip - rst set two offset chimney blocks in sequence,
rearward. This leaves a distance of 9-3/4” from the front face of
the smoke dome to the front face of the DM outer casing once
the outer casing block is set in position. (Figure 57)
Greater offset distances can be accomplished by
building with more offset chimney blocks. (Figure 56)
Offset block Support Foundations:
It is required that every third Isokern offset chimney
block in the sequence be supported down to footings via concrete
block or steel support columns.
Plan replace and DM chimney systems carefully
before foundations are laid to assure that proper footings are
available to support Isokern offset blocks chimney run.
Calculate Offset Distance:
To calculate the distance of Isokern offset chimney travel in a
straight line to the right, left or to the rear of the rebox/smoke
dome assembly, proceed as follows:
Refer to Figure 58: temporarily dry set a DM outer
casing block in its proper location on top of the completed
rebox/smoke dome assembly as though starting a straight
chimney.
If the offset sequence is to move to the left then, starting
from the right side of the temporary DM outer casing measure
left ward to the far face of the overhead obstruction that needs to
be bypassed by the vertical chimney run.
For accurate measuring drop a plumb line down from
the far face of overhead obstruction to the level of the top of
the smoke dome assembly. Measure from the far side of the
temporary DM outer casing to the plumb line.
This measurement, taken in inches and divided by
three (three inches of horizontal travel per offset block) gives
the total number of offset blocks needed to accomplish the
required travel distance.
To calculate the height that the offset block
sequence will require, take the total number of offset blocks
needed to accomplish the travel distance (described above)
multiplied by 6”. This number is the height (inches) that the
offset sequence will require.
FIGURE 55
FIGURE 56
FIGURE 57
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