Page 21
TABLE 7
CAPACITY OF TYPE B DOUBLE-WALL VENT WITH SINGLE-WALL METAL CONNECTORS
SERVING TWO OR MORE CATEGORY I APPLIANCES − VENT CONNECTOR CAPACITY
Vent
Connector
Vent and Connector Diameter − D (inches)
Vent
Height
Connector
Rise
4 Inch
5 Inch
6 Inch
7 Inch
Height
H
(feet)
Rise
R
(feet)
Appliance Input Rating in Thousands of Btu Per Hour
(feet)
(feet)
MIN
MAX
MIN
MAX
MIN
MAX
MIN
MAX
1
NR
NR
NR
NR
NR
NR
207
223
6
2
NR
NR
NR
NR
168
182
215
251
6
3
NR
NR
121
131
174
198
222
273
1
79
87
116
138
177
214
238
291
15
2
83
94
121
150
185
230
246
314
3
87
100
127
160
193
243
255
333
1
77
110
113
175
169
278
226
380
30
2
81
115
117
185
177
290
236
397
3
85
119
122
193
185
300
244
412
TABLE 8
CAPACITY OF TYPE B DOUBLE-WALL VENTS WITH SINGLE-WALL METAL CONNECTORS
SERVING TWO OR MORE CATEGORY I APPLIANCES − COMMON VENT CAPACITY
Vent
Common Vent Diameter − D (inches)
Vent
Height
4 Inch
5 Inch
6 Inch
7 Inch
Height
H
(feet)
Appliance Input Rating in Thousands of Btu Per Hour
(feet)
FAN + FAN
FAN + NAT
FAN + FAN
FAN + NAT
FAN + FAN
FAN + NAT
FAN + FAN
FAN + NAT
6
89
78
136
113
200
158
304
244
8
98
87
151
126
218
173
331
269
10
106
94
163
137
237
189
357
292
15
121
108
189
159
275
221
416
343
20
131
118
208
177
305
247
463
383
30
145
132
236
202
350
286
533
446
Removal of the Furnace from Common Vent
In the event that an existing furnace is removed from a
venting system commonly run with separate gas ap-
pliances, the venting system is likely to be too large to prop-
erly vent the remaining attached appliances. The following
test should be conducted while each appliance in operation
and the other appliances not in operation remain con-
nected to the common venting system. If the venting sys-
tem has been installed improperly, the system must be
corrected as indicated in the general venting requirements
section.
1 − Seal any unused openings in the common venting
system.
2 − Visually inspect the venting system for proper size and
horizontal pitch. Determine there is no blockage or re-
striction, leakage, corrosion, or other deficiencies which
could cause an unsafe condition.
3 − To the extent that it is practical, close all building doors
and windows and all doors between the space in which
the appliances remaining connected to the common
venting system are located and other spaces of the build-
ing. Turn on clothes dryers and any appliances not con-
nected to the common venting system. Turn on any
exhaust fans, such as range hoods and bathroom ex-
hausts, so they will operate at maximum speed. Do not
operate a summer exhaust fan. Close fireplace dampers.
4 − Follow the lighting instructions. Place the appliance being
inspected in operation. Adjust thermostat so appliance
will operate continuously.
5 − Test for spillage of the flue gases at the draft hood relief
opening after 5 minutes of main burner operation. Use
the flame of a match or candle, or smoke from a cigarette,
cigar or pipe.
6 − After determining that each appliance remaining con-
nected to the common venting system properly vents
when tested as indicated instep 3, return doors, windows,
exhaust fans, fireplace dampers and any other gas−burn-
ing appliance to their previous condition of use.
7 − If improper venting is observed during any of the
above tests, the common venting system must be cor-
rected. The common venting system should be re-
sized to approach the minimum size as determined by
using the appropriate tables in appendix G in the cur-
rent standards of the National Fuel Gas Code ANSI
Z223.1 /NFPA54 in the USA, and the appropriate
Category 1 Natural Gas appliances venting sizing
tables in the current standards of the CSA−B149.1
Natural Gas Installation Code in Canada.
