Page 19
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 applianc-
es, the venting system is likely to be too large to properly
vent the remaining attached appliances.
Conduct the following test while each appliance is oper-
ating and the other appliances (which are not operating)
remain connected to the common venting system. If the
venting system has been installed improperly, you must
correct the system as indicated in the general venting re-
quirements section.
TABLE 4
Vent Connector Capacity
Type B Double-Wall Vents with Type B Double-Wall Connectors
Serving Two or More Category I Appliances
Height
H
(feet)
Lateral
L
(feet)
Vent and Connector Diameter - D (inches)
3 inch 4 inch 5 inch 6 inch
Appliance Input Rating in Thousands of Btu Per Hour
Min Max Min Max Min Max Min Max
6
1 22 37 35 66 46 106 58 164
2 23 41 37 75 48 121 60 183
3 24 44 38 81 49 132 62 199
8
1 22 40 35 72 49 114 64 176
2 23 44 36 80 51 128 66 195
3 24 47 37 87 53 139 67 210
10
1 22 43 34 78 49 123 65 189
2 23 47 36 86 51 136 67 206
3 24 50 37 92 52 146 69 220
15
1 21 50 33 89 47 142 64 220
2 22 53 35 96 49 153 66 235
3 24 55 36 102 51 163 68 248
20
1 21 54 33 99 46 157 62 246
2 2 57 34 105 48 167 64 259
3 23 60 35 110 50 176 66 271
30
1 20 62 31 113 45 181 60 288
2 21 64 33 118 47 190 62 299
3 22 66 34 123 48 198 64 309
TABLE 5
Common Vent Capacity
Type B Double-Wall Vents with Type B Double-Wall Connectors
Serving Two or More Category I Appliances
Vent
Height
H
(feet)
Vent and Connector Diameter - D (inches)
4 inch 5 inch 7 inch 7 inch
Appliance Input Rating in Thousands of Btu Per Hour
FAN + FAN FAN + NAT FAN + FAN FAN + NAT FAN + FAN FAN + NAT FAN + FAN FAN + NAT
6 92 81 140 116 204 161 309 248
8 101 90 155 129 224 178 339 275
10 110 97 169 141 243 194 367 299
15 125 112 195 164 283 228 427 352
20 136 123 215 183 314 255 475 394
30 152 138 244 210 361 297 547 459
IMPORTANT
CARBON MONOXIDE POISONING HAZARD
Failure to follow the steps outlined below for each
appliance connected to the venting system being
placed into operation could result in carbon monoxide
poisoning or death. The following steps shall be
followed for each appliance connected to the venting
system being placed into operation, while all other
appliances connected to the venting system are not in
operation:
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