Page 622 - 2018_IRC

FUEL GAS

Category I appliances to maintain a nonpositive vent static 3. Vents for appliance draft hood outlets or flue collars
pressure when tested in accordance with nationally recog- larger than 12 inches (305 mm) in diameter are not
nized standards. reduced more than two table sizes.
FAN-ASSISTED COMBUSTION SYSTEM. An appliance 4. The maximum capacity listed in the tables for a fan-
equipped with an integral mechanical means to either draw or assisted appliance is reduced by 10 percent (0.90 ×
force products of combustion through the combustion cham- maximum table capacity).
ber or heat exchanger.
5. The draft hood outlet is greater than 4 inches (102
FAN Min. The minimum input rating of a Category I fan- mm) in diameter. Do not connect a 3-inch-diameter
assisted appliance attached to a vent or connector. (76 mm) vent to a 4-inch-diameter (102 mm) draft
FAN Max. The maximum input rating of a Category I fan- hood outlet. This provision shall not apply to fan-
assisted appliance attached to a vent or connector. assisted appliances.
NAT Max. The maximum input rating of a Category I draft- G2428.2.3 (504.2.3) Vent offsets. Single-appliance vent-
hood-equipped appliance attached to a vent or connector. ing configurations with zero (0) lateral lengths in Tables
G2428.2(1) and G2428.2(2) shall not have elbows in the
FAN + FAN. The maximum combined appliance input rat- venting system. Single-appliance venting configurations
ing of two or more Category I fan-assisted appliances with lateral lengths include two 90-degree (1.57 rad)
attached to the common vent. elbows. For each additional elbow up to and including 45
FAN + NAT. The maximum combined appliance input rat- degrees (0.79 rad), the maximum capacity listed in the
ing of one or more Category I fan-assisted appliances and venting tables shall be reduced by 5 percent. For each
one or more Category I draft-hood-equipped appliances additional elbow greater than 45 degrees (0.79 rad) up to
attached to the common vent. and including 90 degrees (1.57 rad), the maximum capac-
ity listed in the venting tables shall be reduced by 10 per-
NA. Vent configuration is not allowed due to potential for
condensate formation or pressurization of the venting system, cent. Where multiple offsets occur in a vent, the total
or not applicable due to physical or geometric restraints. lateral length of all offsets combined shall not exceed that
specified in Tables G2428.2(1) and G2428.2(2).
NAT + NAT. The maximum combined appliance input rat- G2428.2.4 (504.2.4) Zero lateral. Zero (0) lateral (L)
ing of two or more Category I draft-hood-equipped appli- shall apply only to a straight vertical vent attached to a top
ances attached to the common vent.
outlet draft hood or flue collar.
G2428.2 (504.2) Application of single-appliance vent
Tables G2428.2(1) and G2428.2(2). The application of G2428.2.5 (504.2.5) High-altitude installations. Sea-
Tables G2428.2(1) and G2428.2(2) shall be subject to the level input ratings shall be used when determining maxi-
requirements of Sections G2428.2.1 through G2428.2.17. mum capacity for high-altitude installation. Actual input,
derated for altitude, shall be used for determining mini-
G2428.2.1 (504.2.1) Vent obstructions. These venting mum capacity for high-altitude installation.
tables shall not be used where obstructions, as described in
Section G2427.15, are installed in the venting system. The G2428.2.6 (504.2.6) Multiple input rate appliances. For
installation of vents serving listed appliances with vent appliances with more than one input rate, the minimum
dampers shall be in accordance with the appliance manu- vent capacity (FAN Min) determined from the tables shall
facturer’s instructions or in accordance with the following: be less than the lowest appliance input rating, and the max-
imum vent capacity (FAN Max/NAT Max) determined
1. The maximum capacity of the vent system shall be from the tables shall be greater than the highest appliance
determined using the “NAT Max” column. rating input.
2. The minimum capacity shall be determined as if the G2428.2.7 (504.2.7) Liner system sizing and connec-
appliance were a fan-assisted appliance, using the tions. Listed corrugated metallic chimney liner systems in
“FAN Min” column to determine the minimum masonry chimneys shall be sized by using Table G2428.2(1)
capacity of the vent system. Where the correspond- or G2428.2(2) for Type B vents with the maximum capacity
ing “FAN Min” is “NA,” the vent configuration reduced by 20 percent (0.80 × maximum capacity) and the
shall not be permitted and an alternative venting minimum capacity as shown in Table G2428.2(1) or
configuration shall be utilized. G2428.2(2). Corrugated metallic liner systems installed
G2428.2.2 (504.2.2) Minimum size. Where the vent size with bends or offsets shall have their maximum capacity
determined from the tables is smaller than the appliance further reduced in accordance with Section G2428.2.3. The
draft hood outlet or flue collar, the smaller size shall be 20-percent reduction for corrugated metallic chimney liner
permitted to be used provided that all of the following systems includes an allowance for one long-radius 90-
requirements are met: degree (1.57 rad) turn at the bottom of the liner.
1. The total vent height (H) is not less than 10 feet (3048 Connections between chimney liners and listed double-
mm). wall connectors shall be made with listed adapters
designed for such purpose.
2. Vents for appliance draft hood outlets or flue collars
12 inches (305 mm) in diameter or smaller are not G2428.2.8 (504.2.8) Vent area and diameter. Where the
reduced more than one table size. vertical vent has a larger diameter than the vent connector,

2018 INTERNATIONAL RESIDENTIAL CODE ® 597
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