Heatilator • LM42 • Installers Manual • 4087-901 • Rev A • 04/14/16
21
B. Offsets/Returns
A 30° Elbow (measured from the vertical) is the largest that can be used in an offset. A 30° Elbow may not be combined
with another Elbow to make a steeper offset (e.g. two 30° Elbows are not allowed to be put together to form a 60° elbow.).
Avoid Elbows if possible. A totally vertical chimney is more efficient. When Elbows are necessary to avoid obstructions
such as rafters, ridgepoles, or joists, you are only allowed to use 2 pair of Elbows in any one chimney system. Horizontal
runs of chimney violate building code and are not allowed.
• An offset and return can be used as a single entity or separated by chimney section(s).
WARNING!
Risk of Fire! DO NOT
use offset/returns greater than 30° from vertical. Chimney draft will be restricted and
could cause overheating and fire.
• Measure the shift needed to avoid the overhead obstruction. Refer to dimension A in Figure 4.2.
• Find the appropriate A dimension listed in Table 4.3. The B dimension coinciding with the A dimension measurement in
Table 4.3 represents the required vertical clearance needed to complete the offset/return.
• Read across the chart to find the number of chimney sections/model numbers needed between the offset and return.
Figure 4.2 Chimney Offset/Return
Table 4.3 Offset Dimensions
A
B
1-1/4 in. (32 mm)
OVERLAP
30°
Max
Example:
Your “A” dimension from Figure 4.2 is 14 1/2 in. (368
mm). Using Table 4.3 the dimension closest to, but not
less than 14 1/2 in. (368 mm) is 14 1/2 in. (368 mm) us
-
ing a 30° offset/return.
You determine from the table that you need 34 1/8 in.
(867 mm) (Dimension “B”) between the offset and re
-
turn.
The chimney component that best fits your application is
one SL324.
15-degree
30-degree
SL306 SL312 SL318 SL324 SL336 SL348
A
B
A
B
in.
mm
in.
mm
in.
mm
in.
mm
1 5/8
41
13 3/8
340
3 5/8
92
15 1/2
394
-
-
-
-
-
-
2 7/8
73
17 3/4
451
5 1/2
140
18 5/8
473
1
-
-
-
-
-
4 1/8
102
22 3/8
568
7 1/4
184 21 3/4
552
2
-
-
-
-
-
4 1/2
114
23 5/8
600
8 1/2
216
23 3/4
603
-
1
-
-
-
-
5 3/4
146
28 1/4
718
10 1/4
260
27
686
1
1
-
-
-
-
6
152
29 3/8
746
11 1/2
292
29
737
-
-
1
-
-
-
7 1/4
184
34
864 13 1/4
337 32 1/8 816
-
2
-
-
-
-
7 3/4
197
36 1/8
918 14 1/2
368
34 1/8
867
-
-
-
1
-
-
8 3/4
222
39 3/4
1010
16 1/4 413
37 3/8
949
1
-
-
1
-
-
10 3/8
264
45 5/8 1159 19 1/4 489 42 1/2
1080
-
-
2
-
-
-
10 5/8 270
46 3/4
1187 20 1/2 521
44 5/8
1133
-
-
-
-
1
-
11 7/8 302
51 3/8 1305
22 1/4
565
47 3/4
1213
1
-
-
-
1
-
13 1/2
243
57 1/4 1454 25 1/4 641
52 7/8
1343
-
-
-
2
-
-
13 3/4 349
58 3/8
1483
26 1/2 673
55
1397
-
-
-
-
-
1
15
381
63
1600
28 1/4
718 58 1/8
1476
1
-
-
-
-
1
16 1/2
419
68 3/4 1746 31 1/4 794 63 1/4
1607
-
1
-
-
-
1
18
457
74 5/8 1895 34 1/4
870 68 1/2
1740
-
-
1
-
-
1
19 5/8 498
80 3/8
2042 37 1/4 946 73 3/4
1873
-
-
-
1
-
1
20 5/8
524
84 1/8
2137
39 1/8 994
76 7/8
1953
1
-
-
1
-
1
22 3/4
578
91 7/8 2334 43 1/4 1099 84 1/8
2137
-
-
-
-
1
1
24
610
96 1/2 2451 45 1/8 1146 87 1/4
2216
1
-
-
-
1
1
25 7/8 657 103 1/2
2629 49 1/4
1251
94 1/2 2400
-
-
-
-
-
2
Proper assembly of air-cooled chimney parts result in an overlap at chimney joints of 1-1/4 in. (32 mm). Effective
length is built into this chart.
