Page 112 - 2018_IFGC

CHIMNEYS AND VENTS

504.3.5 Common vertical vent offset. Where the com- est draft hood outlet or flue collar entering that segment
mon vertical vent is offset, the maximum capacity of the and the centerline of the next higher interconnection tee.
common vent shall be reduced in accordance with Section 504.3.14 Multistory lowest portion sizing. The size of
504.3.6. The horizontal length of the common vent offset the lowest connector and of the vertical vent leading to the
1
(L ) shall not exceed 1 / feet for each inch (18 mm per lowest interconnection of a multistory system shall be in
2
o
mm) of common vent diameter (D). Where multiple off- accordance with Table 504.2(1) or 504.2(2) for available
sets occur in a common vent, the total horizontal length of total height (H) up to the lowest interconnection.
1
all offsets combined shall not exceed 1 / feet for each inch
2
(18 mm per mm) of common vent diameter (D). 504.3.15 Multistory common vents. Where used in mul-
tistory systems, vertical common vents shall be Type B
504.3.6 Elbows in vents. For each elbow up to and includ- double wall and shall be installed with a listed vent cap.
ing 45 degrees (0.79 rad) in the common vent, the maxi-
mum common vent capacity listed in the venting tables 504.3.16 Multistory common vent offsets. Offsets in
shall be reduced by 5 percent. For each elbow greater than multistory common vent systems shall be limited to a sin-
45 degrees (0.79 rad) up to and including 90 degrees (1.57 gle offset in each system, and systems with an offset shall
rad), the maximum common vent capacity listed in the comply with all of the following:
venting tables shall be reduced by 10 percent. 1. The offset angle shall not exceed 45 degrees (0.79
rad) from vertical.
504.3.7 Elbows in connectors. The vent connector capac-
ities listed in the common vent sizing tables include allow- 2. The horizontal length of the offset shall not exceed
1
ance for two 90-degree (1.57 rad) elbows. For each 1 / feet for each inch (18 mm per mm) of common
2
additional elbow up to and including 45 degrees (0.79 vent diameter of the segment in which the offset is
rad), the maximum vent connector capacity listed in the located.
venting tables shall be reduced by 5 percent. For each 3. For the segment of the common vertical vent con-
elbow greater than 45 degrees (0.79 rad) up to and includ- taining the offset, the common vent capacity listed in
ing 90 degrees (1.57 rad), the maximum vent connector the common venting tables shall be reduced by 20
capacity listed in the venting tables shall be reduced by 10 percent (0.80 × maximum common vent capacity).
percent.
4. A multistory common vent shall not be reduced in
504.3.8 Common vent minimum size. The cross-sec- size above the offset.
tional area of the common vent shall be equal to or greater
504.3.17 Vertical vent maximum size. Where two or
than the cross-sectional area of the largest connector.
more appliances are connected to a vertical vent or chim-
504.3.9 Common vent fittings. At the point where tee or ney, the flow area of the largest section of vertical vent or
wye fittings connect to a common vent, the opening size of chimney shall not exceed seven times the smallest listed
the fitting shall be equal to the size of the common vent. appliance categorized vent areas, flue collar area or draft
Such fittings shall not be prohibited from having reduced- hood outlet area unless designed in accordance with
size openings at the point of connection of appliance vent approved engineering methods.
connectors.
504.3.18 Multiple input rate appliances. For appliances
504.3.9.1 Tee and wye fittings. Tee and wye fittings with more than one input rate, the minimum vent connec-
connected to a common gas vent shall be considered to tor capacity (FAN Min) determined from the tables shall
be part of the common gas vent and shall be con- be less than the lowest appliance input rating, and the
structed of materials consistent with that of the com- maximum vent connector capacity (FAN Max or NAT
mon gas vent. Max) determined from the tables shall be greater than the
504.3.10 High-altitude installations. Sea-level input rat- highest appliance input rating.
ings shall be used when determining maximum capacity 504.3.19 Liner system sizing and connections. Listed,
for high-altitude installation. Actual input (derated for alti- corrugated metallic chimney liner systems in masonry
tude) shall be used for determining minimum capacity for chimneys shall be sized by using Table 504.3(1) or
high-altitude installation. 504.3(2) for Type B vents, with the maximum capacity
504.3.11 Connector rise measurement. Connector rise reduced by 20 percent (0.80 × maximum capacity) and the
(R) for each appliance connector shall be measured from minimum capacity as shown in Table 504.3(1) or
the draft hood outlet or flue collar to the centerline where 504.3(2). Corrugated metallic liner systems installed with
the vent gas streams come together. bends or offsets shall have their maximum capacity further
reduced in accordance with Sections 504.3.5 and 504.3.6.
504.3.12 Vent height measurement. For multiple appli-
The 20-percent reduction for corrugated metallic chimney
ances all located on one floor, available total height (H)
shall be measured from the highest draft hood outlet or liner systems includes an allowance for one long-radius
flue collar up to the level of the outlet of the common vent. 90-degree (1.57 rad) turn at the bottom of the liner. Where
double-wall connectors are required, tee and wye fittings
504.3.13 Multistory height measurement. For multistory used to connect to the common vent chimney liner shall be
installations, available total height (H) for each segment of listed double-wall fittings. Connections between chimney
the system shall be the vertical distance between the high-

2018 INTERNATIONAL FUEL GAS CODE ® 99
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