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TABLE 13
CAPACITY OF TYPE B DOUBLE-WALL VENT WITH SINGLE-WALL METAL CONNECTORS
SERVING TWO OR MORE CATEGORY I APPLIANCES
VENT CONNECTOR CAPACITY
Vent and Connector Diameter - D (inches)
Vent
Hei
ht
onnector
Rise
3 Inch 4 Inch 5 Inch 6 Inch
H
R
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 NR NR
6
2 NR NR NR NR NR NR 168 182
3 NR NR NR NR 121 131 174 198
1 NR NR 79 87 116 138 177 214
15
2 NR NR 83 94 121 150 185 230
3 NR NR 87 100 127 160 193 243
1 47 60 77 110 113 175 169 278
30
2 50 62 81 115 117 185 177 290
3 54 64 85 119 122 193 185 300
TABLE 14
CAPACITY OF TYPE B DOUBLE-WALL VENTS WITH SINGLE-WALL METAL CONNECTORS
SERVING TWO OR MORE CATEGORY I APPLIANCES
COMMON VENT CAPACITY
Common Vent Diameter - D (inches)
ent
Hei
ht
4 Inch 5 Inch 6 Inch 7 Inch
H
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 Unit from Common Venting System
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
properly vent the remaining attached appliances. The fol-
lowing test should be conducted while each appliance is in
operationandthe other appliancesnot in operationremain
connected to the common venting system. If the venting
system has been installed improperly, the system must be
corrected as outlined in the previous section.
1 - Seal any unused openings in the common venting
system.
2 - Visually inspect the venting system for proper size
and horizontal pitch and determine there is no block-
age or restriction, leakage, corrosion and other defi-
ciencies which could cause an unsafe condition.
3 - Insofar as is practical, close all building doors and win-
dows and all doors between the space in which the ap-
pliances remaining connected to the common venting
system are located and other spaces of the building.
Turn on clothes dryers and any appliances not con-
nectedtothecommonventing system. Turnon any ex-
haust 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 damp-
ers.
4 - Following the lighting instruction, place the appliance
being inspected in operation. Adjust thermostat so ap-
pliance will operate continuously.
5 - Testfor spillage atthe draft hoodrelief 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 it has been determined that each appliance re-
maining connected to the common venting system
properly vents when tested as outlined above, return
doors, windows, exhaust fans,fireplace dampers and
any other gas burning 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
corrected. The common ventingsystem should be re-
sizedtoapproachtheminimum size as determinedby
using the appropriate tables in appendix G in the cur-
rent standards of the National Fuel Gas Code ANSI
Z223-1.
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