Offset Calculations; Installing Offsets - Lennox Hearth Products Magna-Fire LS43ST Installation Instructions Manual

The offset and return elbows may be attached
together, or a section or sections of chimney
may be used between, but do not exceed 20'
(6.1 m) in total length between elbows ( see
Figure 36 ). If sections of pipe exceed 10' (3 m)
between elbows, a chimney stabilizer must be
used at the midpoint. The stabilizer support
straps must be attached under tension (in
shear) to structural framing members above.
When two sets of offset elbows are used, the
maximum combined length of chimney used
between elbows cannot exceed 20' (6.1 m)
( see Figures 37 and 38 ). Example: If C
(3m) then C cannot exceed 10' (3 m).
2
If an offset exceeds 6' in length, each chimney
joint beyond the first 6' of offset to the return
elbow, must be secured by a No. 8 x ¹⁄₂" sheet
mental screw located at the underside of the
joint ( Figure 39 ).
Chimney
Section
4'
6'
Figure 39
A ¹⁄₈" (3 mm) diameter hole must be drilled in
the chimney joint using a ¹⁄₈" (3 mm) diameter
drill. Hole should be drilled in center of joint
overlap ( Figure 40 ). Be sure to drill only through
the outer chimney casting. Do not puncture the
inner flue.
Underside of Chimney
Figure 40
Maximum offset of the chimney system is 30°.
Two offset elbows must not be assembled to
form a 60° offset. However, two sets of offset
and return elbows may be used on a single flue
system, provided the total height of the system
exceeds 22' (5.6 m).
Return elbow support straps must be securely
attached under tension (in shear) to structural
framing members above.

OFFSET CALCULATIONS

= 10'
1
1. Use Offset Chart to determine amount of
horizontal offset (A) and height (B) for various
chimney sections.
2. Use "Height of Chimney Only" column to
determine combinations of pipe used above
return elbow to achieve desired heights. Refer-
ence Components Effective Height Chart in
vertical elevation chart section.
3. Use Elevation Chart as job estimator only.
Joints
Add necessary firestop spacers and stabilizers
as required. Firestop spacers must be used as
shown in Figures 20 and 21 and stabilizers as
shown in Figure 25 .

INSTALLING OFFSETS

No. 8 x ¹⁄₂" SMS
First, review Offset Elevation Chart and Figure
35 on page 14 for reference.
Step 1. Determine the offset distance where
chimney is to pass through the first ceiling-
dimension "A." To find this point on your ceil-
ing, first determine the center point for a verti-
cal chimney following the instructions for ver-
tical installation.
Measure height to the ceiling from the top of
fireplace-dimension "B." Use Offset Elevation
Chart to find dimension "A." Mark point where
you will drive your nail to show the center point
for your offset ceiling cut.
Step 2. Proceed by using the Straight Up Instal-
lation Instructions for cutting and framing ceil-
ing and roof openings.
Note: See "Framing and Dimension" Chart for
the sizes of the ceiling and roof openings. The
size of the roof opening varies with the degree
of pitch of the roof.
NOTE: DIAGRAMS & ILLUSTRATIONS NOT TO SCALE.
OFFSET ELBOW ASSEMBLY
Offset elbows install the same as chimney
sections. First, snap the inner section INTO the
preceding inner section of flue. Check connec-
tion by pulling up slightly to ensure a tight fit.
Next, the outer sections snap locks OVER the
preceding outer section of chimney. Again,
check outer section by pulling up slightly to
ensure proper connection is made.
RETURN ELBOW ASSEMBLY
Return elbows install the same way as round
terminations and stabilizers:
Step 1. Hold return elbow over top of last
chimney section.
Step 2. Center inner slip section into inner flue
pipe-slip down.
Step 3. Center outer locking section over outer
chimney pipe-push down until locking joint has
firmly engaged.
Step 4. Pull up slightly on return elbow to
ensure locking joint has firmly engaged.
Step 5. Secure support straps to framing
members by nailing under tension in sheer
( Figure 41 ).
Return Elbow
Figure 41
Note: The return elbow assembly performs the
same function as a stabilizer. Consider this
when determining the need for a stabilizer.
Note: Do not apply excessive pressure to any
subsequent chimney section following return
elbow assembly when installing. Ensure sub-
sequent chimney sections are securely attached
by testing as noted above.
15