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16- If vent connectors are combined prior to entering the
common vent, the maximum common vent capacity
listed in the common venting tables must be reduced
by 10%, the equivalent of one 90
elbow (0.90 x max
imum common vent capacity).
17- The common vent diameter must always be at least
as large as the largest vent connector diameter.
18- In no case, shall the vent connector be sized more
than two consecutive table size diameters over the
size of the draft hood outlet or flue collar outlet.
19- Do not install a manual damper, barometric draft reg
ulator or flue restrictor between the furnace and the
chimney.
20- When connecting this appliance to an existing dedi
cated or common venting system, the venting sys
tem, must be inspected for signs of corrosion, and
general condition. The sizing of the vent system must
be reviewed and must conform to these instructions
and the provided venting tables. If the existing sys
tem is in conflict with these requirements, the venting
system must be resized.
TABLE 3
CAPACITY OF TYPE B DOUBLE-WALL VENTS WITH TYPE B DOUBLE-WALL CONNECTORS
SERVING A SINGLE CATEGORY I APPLIANCE
Vent and Connector Diameter - D (inches)
Height
Lateral
3 Inch
4 Inch
5 Inch
6 Inch
Height
H (feet)
Lateral
L (feet)
Appliance Input Rating in Thousands of Btu Per Hour
MIN.
MAX.
MIN.
MAX.
MIN.
MAX.
MIN.
MAX.
0
0
78
0
152
0
251
0
375
6
2
13
51
18
97
27
157
32
232
6
4
21
49
30
94
39
153
50
227
6
25
46
36
91
47
149
59
223
0
0
84
0
165
0
276
0
415
8
2
12
57
16
109
25
178
28
263
8
5
23
53
32
103
42
171
53
255
8
28
49
39
98
51
164
64
247
0
0
88
0
175
0
295
0
447
10
2
12
61
17
118
23
194
26
289
10
5
23
57
32
113
41
187
52
280
10
30
51
41
104
54
176
67
267
0
0
94
0
191
0
327
0
502
2
11
69
15
136
20
226
22
339
15
5
22
65
30
130
39
219
49
330
10
29
59
40
121
51
206
64
315
15
35
53
48
112
61
195
76
301
0
0
97
0
202
0
349
0
540
2
10
75
14
149
18
250
20
377
20
5
21
71
29
143
38
242
47
367
20
10
28
64
38
133
50
229
62
351
15
34
58
46
124
59
217
73
337
20
48
52
55
116
69
206
84
322
0
0
100
0
213
0
374
0
587
2
9
81
13
166
14
283
18
432
5
21
77
28
160
36
275
45
421
30
10
27
70
37
150
48
262
59
405
15
33
64
44
141
57
249
70
389
20
56
58
53
132
66
237
80
374
30
NR
NR
73
113
88
214
104
346
NOTE: Single appliance venting configurations with zero lateral lengths are assumed to have no elbows in the vent system. For all other vent configurations, the
vent system is assumed to have two 90
elbows. For each additional 90
elbow or equivalent (for example two 45
elbows equal one 90
elbow) beyond two, the
maximum capacity listed in the venting table should be reduced by 10 percent (0.90 x maximum listed capacity).
