Lennox EL280UH Installation Instructions Manual page 18

16 − Vent connectors serving Category I appliances shall
not be connected to any portion of mechanical draft
systems operating under positive pressure such as
Category III or IV venting systems.
17 − 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 maximum
common vent capacity).
18 − The common vent diameter must always be at least as
large as the largest vent connector diameter.
19 − In no case, shall the vent connector be sized more than
Capacity of Type B Double−Wall Vents with Type B Double−Wall Connectors
Height Lateral
H L
(feet) (feet)
0
2
6
4
6
0
2
8
5
8
0
2
10
5
10
0
2
5
15
10
15
0
2
5
20
10
15
20
0
2
5
10
30
15
20
30
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 maxi-
mum listed capacity).
Serving a Single Category I Appliance
3 Inch
Appliance Input Rating in Thousands of Btu Per Hour
MIN MAX MIN
0 78
13 51 18
21 49 30
25 46 36
0 84
12 57 16
23 53 32
28 49 39
0 88
12 61 17
23 57 32
30 51 41
0 94
11 69 15
22 65 30
29 59 40
35 53 48
0 97
10 75 14
21 71 29
28 64 38
34 58 46
48 52 55
0 100
9 81 13
21 77 28
27 70 37
33 64 44
56 58 53
NA NA 73
two consecutive table size diameters over the size of
the draft hood outlet or flue collar outlet.
20 − Do not install a manual damper, barometric draft regu-
lator or flue restrictor between the furnace and the
chimney.
21 − When connecting this appliance to an existing dedi-
cated or common venting system, you must inspect the
venting system's general condition and look for signs
of corrosion. The existing vent pipe size must conform
to these instructions and the provided venting tables. If
the existing venting system does not meet these re-
quirements, it must be resized.
TABLE 3
Vent and Connector Diameter − D (inches)
4 Inch
MAX MIN
0 152 0
97 27
94 39
91 47
0 165 0
109 25
103 42
98 51
0 175 0
118 23
113 41
104 54
0 191 0
136 20
130 39
121 51
112 61
0 202 0
149 18
143 38
133 50
124 59
116 69
0 213 0
166 14
160 36
150 48
141 57
132 66
113 88
Page 18
5 Inch 6 Inch
MAX MIN
251 0
157 32
153 50
149 59
276 0
178 28
171 53
164 64
295 0
194 26
187 52
176 67
327 0
226 22
219 49
206 64
195 76
349 0
250 20
242 47
229 62
217 73
206 84
374 0
283 18
275 45
262 59
249 70
237 80
214 104
MAX
375
232
227
223
415
263
255
247
447
289
280
267
502
339
330
315
301
540
377
367
351
337
322
587
432
421
405
389
374
346