Page 625 - 2018_IRC

FUEL GAS

rad) turn at the bottom of the liner. Where double-wall must be sized using Table G2428.3(2) or G2428.3(4), as
connectors are required, tee and wye fittings used to con- appropriate.
nect to the common vent chimney liner shall be listed dou- G2428.3.19 (504.3.23) Draft hood conversion accesso-
ble-wall fittings. Connections between chimney liners and ries. Draft hood conversion accessories for use with
listed double-wall fittings shall be made with listed masonry chimneys venting listed Category I fan-assisted
adapter fittings designed for such purpose. appliances shall be listed and installed in accordance with
G2428.3.16 (504.3.20) Chimney and vent location. the manufacturer’s instructions for such listed accessories.
Tables G2428.3(1), G2428.3(2), G2428.3(3) and G2428.3.20 (504.3.24) Multiple sizes permitted. Where
G2428.3(4) shall be used only for chimneys and vents not a table permits more than one diameter of pipe to be used
exposed to the outdoors below the roof line. A Type B for a connector or vent, all of the permitted sizes shall be
vent or listed chimney lining system passing through an permitted to be used.
unused masonry chimney flue shall not be considered to
be exposed to the outdoors. Where vents extend outdoors G2428.3.21 (504.3.25) Table interpolation. Interpolation
above the roof more than 5 feet (1524 mm) higher than shall be permitted in calculating capacities for vent dimen-
required by Figure G2427.6.4 and where vents terminate sions that fall between table entries.
in accordance with Section G2427.6.4, Item 2, the outdoor G2428.3.2 (504.3.2 Extrapolatio prohibited.
portion of the vent shall be enclosed as required by this Extrapolation beyond the table entries shall not be permit-
section for vents not considered to be exposed to the out- ted.
doors or such venting system shall be engineered. A Type G2428.3.23 (504.3.27) Engineering calculations. For
B vent shall not be considered to be exposed to the out- vent heights less than 6 feet (1829 mm) and greater than
doors where it passes through an unventilated enclosure or shown in the tables, engineering methods shall be used to
chase insulated to a value of not less than R8.
calculate vent capacities.
G2428.3.17 (504.3.21) Connector maximum and mini- G2428.3.24 (504.3.28) Height entries. Where the actual
mum size. Vent connectors shall not be increased in size height of a vent falls between entries in the height column
more than two sizes greater than the listed appliance cate- of the applicable table in Tables G2428.3(1) through
gorized vent diameter, flue collar diameter or draft hood G2428.3(4), either interpolation shall be used or the lower
outlet diameter. Vent connectors for draft-hood-equipped appliance input rating shown in the table shall be used for
appliances shall not be smaller than the draft hood outlet FAN Max and NAT Max column values and the higher
diameter. Where a vent connector size(s) determined from appliance input rating shall be used for the FAN Min col-
the tables for a fan-assisted appliance(s) is smaller than umn values.
the flue collar diameter, the use of the smaller size(s) shall
be permitted provided that the installation complies with
all of the following conditions: SECTION G2429 (505)
1. Vent connectors for fan-assisted appliance flue col- DIRECT-VENT, INTEGRAL VENT,
lars 12 inches (305 mm) in diameter or smaller are MECHANICAL VENT AND
not reduced by more than one table size [for exam- VENTILATION/EXHAUST HOOD VENTING
ple, 12 inches to 10 inches (305 mm to 254 mm) is a G2429.1 (505.1) General. The installation of direct-vent and
one-size reduction] and those larger than 12 inches integral vent appliances shall be in accordance with Section
(305 mm) in diameter are not reduced more than two G2427. Mechanical venting systems shall be designed and
table sizes [for example, 24 inches to 20 inches (610 installed in accordance with Section G2427.
mm to 508 mm) is a two-size reduction].
2. The fan-assisted appliance(s) is common vented
with a draft-hood-equipped appliance(s). SECTION G2430 (506)
3. The vent connector has a smooth interior wall. FACTORY-BUILT CHIMNEYS
G2430.1 (506.1) Listing. Factory-built chimneys for building
G2428.3.18 (504.3.22) Component commingling. Com- heating appliances producing flue gases having a temperature
binations of pipe sizes and combinations of single-wall not greater than 1,000ºF (538ºC), measured at the entrance to
and double-wall metal pipe shall be allowed within any the chimney, shall be listed and labeled in accordance with
connector run(s) or within the common vent, provided that UL 103 and shall be installed and terminated in accordance
all of the appropriate tables permit all of the desired sizes with the manufacturer’s instructions.
and types of pipe, as if they were used for the entire length
of the subject connector or vent. Where single-wall and G2430.2 (506.2) Support. Where factory-built chimneys are
Type B double-wall metal pipes are used for vent connec- supported by structural members, such as joists and rafters,
tors within the same venting system, the common vent such members shall be designed to support the additional
load.

600 2018 INTERNATIONAL RESIDENTIAL CODE ®
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