Page 89 - 2018_IMC

DUCT SYSTEMS

602.3 Stud cavity and joist space plenums. Stud wall cavi- SECTION 603
ties and the spaces between solid floor joists to be utilized as DUCT CONSTRUCTION AND INSTALLATION
air plenums shall comply with the following conditions: 603.1 General. An air distribution system shall be designed
1. Such cavities or spaces shall not be utilized as a plenum and installed to supply the required distribution of air. The
for supply air. installation of an air distribution system shall not affect the
fire protection requirements specified in the International
2. Such cavities or spaces shall not be part of a required
fire-resistance-rated assembly. Building Code. Ducts shall be constructed, braced, reinforced
and installed to provide structural strength and durability.
3. Stud wall cavities shall not convey air from more than
one floor level. 603.2 Duct sizing. Ducts installed within a single dwelling
unit shall be sized in accordance with ACCA Manual D, the
4. Stud wall cavities and joist space plenums shall comply appliance manufacturer’s installation instructions or other
with the floor penetration protection requirements of approved methods. Ducts installed within all other buildings
the International Building Code. shall be sized in accordance with the ASHRAE Handbook of
5. Stud wall cavities and joist space plenums shall be iso- Fundamentals or other equivalent computation procedure.
lated from adjacent concealed spaces by approved fire- 603.3 Duct classification. Ducts shall be classified based on
blocking as required in the International Building the maximum operating pressure of the duct at pressures of
Code. positive or negative 0.5, 1.0, 2.0, 3.0, 4.0, 6.0 or 10.0 inches
6. Stud wall cavities in the outside walls of building enve- (1 inch w.c. = 248.7 Pa) of water column. The pressure classi-
lope assemblies shall not be utilized as air plenums. fication of ducts shall equal or exceed the design pressure of
the air distribution in which the ducts are utilized.
[BS] 602.4 Flood hazard. For structures located in flood
hazard areas, plenum spaces shall be located above the eleva- 603.4 Metallic ducts. Metallic ducts shall be constructed as
tion required by Section 1612 of the International Building specified in the SMACNA HVAC Duct Construction Stan-
Code for utilities and attendant equipment or shall be dards—Metal and Flexible.
designed and constructed to prevent water from entering or Exception: Ducts installed within single dwelling units
accumulating within the plenum spaces during floods up to shall have a minimum thickness as specified in Table
such elevation. If the plenum spaces are located below the 603.4.
elevation required by Section 1612 of the International 603.4.1 Minimum fasteners. Round metallic ducts shall
Building Code for utilities and attendant equipment, they be mechanically fastened by means of not less than three
shall be capable of resisting hydrostatic and hydrodynamic sheet metal screws or rivets spaced equally around the
loads and stresses, including the effects of buoyancy, during joint.
the occurrence of flooding up to such elevation.
Exception: Where a duct connection is made that is
partially inaccessible, three screws or rivets shall be

TABLE 603.4
DUCT CONSTRUCTION MINIMUM SHEET METAL THICKNESS FOR SINGLE DWELLING UNITS a
STATIC PRESSURE
1 / 2 -inch water gauge 1-inch water gauge
ROUND DUCT DIAMETER Thickness (inches) Thickness (inches)
(inches) Galvanized Aluminum Galvanized Aluminum
< 12 0.013 0.018 0.013 0.018
12 to14 0.013 0.018 0.016 0.023
15 to 17 0.016 0.023 0.019 0.027
18 0.016 0.023 0.024 0.034
19 to 20 0.019 0.027 0.024 0.034
STATIC PRESSURE
1 / 2 -inch water gauge 1-inch water gauge
RECTANGULAR DUCT DIMENSION Thickness (inches) Thickness (inches)
(inches) Galvanized Aluminum Galvanized Aluminum
≤ 8 0.013 0.018 0.013 0.018
9 to10 0.013 0.018 0.016 0.023
11 to 12 0.016 0.023 0.019 0.027
13 to 16 0.019 0.027 0.019 0.027
17 to 18 0.019 0.027 0.024 0.034
19 to 20 0.024 0.034 0.024 0.034
For SI: 1 inch = 25.4 mm, 1-inch water gauge = 249 Pa.
a. Ductwork that exceeds 20 inches by dimension or exceeds a pressure of 1-inch water gauge shall be constructed in accordance with SMACNA HVAC Duct
Construction Standards—Metal and Flexible.

72 2018 INTERNATIONAL MECHANICAL CODE 
Copyrighted © 2017 by, or licensed to, ICC (ALL RIGHTS RESERVED); licensed to UL, LLC pursuant to License Agreement with ICC. No further reproductions authorized or distribution authorized.
ANY UNAUTHROIZED REPRODUCTION OR DISTRIBUTION IS A VIOLATION OF THE FEDERAL COPYRIGHT ACT AND THE LICENSE AGREEMENT; AND SUBJECT TO CIVIL AND CRIMINAL PENALTIES THEREUNDER.