HVAC Duct Construction
Bob WasilewskiProject Manager, Technical Resources
SMACNA
HVAC Duct Construction Standards
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Today's Program
O 1st 2nd Edition HVAC-DCSOReview Joints and LimitationsOTransverse Joints & ReinforcementsOUse of the Pressure Class TablesOTie Rod Addendum
Documents Preceding 2nd Edition HVAC-DCS
O Low Velocity Systems Duct Manual First Edition 1959 Second Edition 1963 Third Edition 1967
O Low Velocity Duct Construction Standard 1969
Documents Preceding 2nd Edition HVAC-DCS
O Low Pressure Duct Construction Standard Fifth Edition 1976
O High Velocity Duct Systems Manual First Edition 1965
O High Velocity Duct Construction Standards Second Edition 1969
Documents Preceding 2nd Edition HVAC-DCS
O High Pressure Duct Construction Standards Third Edition 1975
O Duct Liner Application Standard First Edition 1971 Second Edition 1975
Documents Preceding 2nd Edition HVAC-DCS
O Flexible Duct Installation Standards First Edition 1979 Second Edition 1980
O HVAC Duct Construction Standards --Metal and Flexible First Edition 1985
Major Changes from First Edition
GENERALO Text edited to be more reader-friendly
O Reading aids added
O Static pressure only as the basis for duct construction classification -- velocity levels deleted (Table 1-1)
Major Changes from First Edition
O Chapter 7 revised to facilitate use for equivalent and comparable tests and ratings
O Model project specification added
O Reminders to designers to show all required fire, smoke, radiation and volume control dampers on contract drawings are accented
Major Changes from First Edition
O Boiler breeching omittedO Volume damper construction is more
specificO Lead radiation shielding addedO Metrics are includedO Air terminal runouts and supports are
revised
Major Changes from First Edition
RECTANGULAR DUCT REVISIONSO Negative pressure construction given for
4", 6", and 10" w.g.
O Six feet reinforcement schedules added
O Reinforcement schedules extended to 120" width
Major Changes from First Edition
O Tie rod alternatives expanded for both positive and negative pressures
O TDC and TDF joint systems included and rated as T-25a and T-25b joints
O T-24a joint added as a modification of T-24
Major Changes from First Edition
O Use of 26 gage added for 4", 6" and 10" pressures
O Trapeze hanger tables expanded to cover the 120" width range
O Duct liner pin schedule adjustedO Infrequently used joints (T-4, 8, 17, 18,
19, 20 and 23) omitted
Major Changes from First Edition
Round, Flexible and Oval Duct RevisionsO Duct pressure classes revised to be positive
and negative at 2", 4" and 10" w.g.O Crimped joint connection length changed
from 1" to 2"O Rectangular branch taps into round added
for straight or 45 degree lead-in-entry
Major Changes from First Edition
O Type 1 reinforcement of oval duct now has an internal tie rod (based on ASHRAE test program)
O Maximum support spacing for round flexible duct and connector changed from 10 feet to 5 feet
O Additional riser support details are provided
DUCT SYSTEMS
SIZINGSFITTINGS, ETC.
FIRE/SMOKEPROTECTION
CODECOMPLIANCE
DUCTCONSTRUCTION
CODECOMPLIANCE
SMACNAHVAC-DCS
2ND ED. 1995
INSPECTION CODECOMPLIANCE
DUCT SYSTEMS
ENGINEERDesign Considerations:
CFM
Static Pressure
Duct Size
Fitting Type
Construction Pressure Class
CONTRACTORConstruction Considerations:
Panel Thickness (Gage)
Pressure Class (as specified)
Panel Width/Height
Joint Type/Spacing
Intermediate Reinforcement Type/Spacing
DEPENDENT VARIABLES
REGULAR DUCTS
+10%+7.5%
Tolerance:Tolerance:
1" on 85"-120"
Class Rating + 25%3/4" on 25"-84"
Field:5/8"on 19"-24"49"-120"
1/2" on 13"-18"W/200 on
Class Rating + 50%3/8" on 12" Dn.1/4" on 48" w.
Lab:Sheet:Joint and Reinf.
Maximum Test Pressure
Maximum Deflection
Duct Systems
O Used for the movement of air in HVAC/Exhaust systems
O Ducts are classified based on maximum operating pressure 0.5" w.g. positive or negative
1.0" w.g. positive or negative
2.0" w.g. positive or negative
Duct Systems (Continued)
O Ducts are classified based on maximum operating pressure 3.0" w.g. positive or negative
4.0" w.g. positive or negative
6.0" w.g. positive or negative
10.0" w.g. positive or negative
TABLE 1-2
STANDARD DUCT SEALING REQUIREMENTS
EXAMPLE 1
ODuct Size 24" x 24"OPressure Class 2" w.g.OSheet StockO Joints/Reinforcements 8 ft / 4 ftOStanding S
EXAMPLE 2
ODuct Size 42" x 24"OPressure Class 3" w.g.O 5 ft Coil LineO Joints/Reinforcements 5 ft / 2 ftOTDC or TDF
MIDPANEL TIE ROD (MPT)
O" w.g. - 6" w.g.
O 37" - 96"
Duct Dimension
ORectangular Duct
Mid Panel Tie Rod Addendum
O Joints All
O Tie Rods Threaded Rod or Tubing/Conduit with Threaded Insert
O Additional Application Tables, Qualifications and Reader Aids Included
FIGURE 1-3 TIE ROD ATTACHMENTS
FIGURE 1-4 TRANSVERSE (GIRTH) JOINTS
FIGURE 1-4 TRANSVERSE (GIRTH) JOINTS
FIGURE 1-4A SPECIAL JOINT PROFILES
FIGURE 1-5 LONGITUDINAL SEAMS RECTANGULAR DUCT
TABLE 1-24 UNREINFORCED DUCT (WALL THICKNESS)
TABLE 1-25T-1 FLAT DRIVE ACCEPTED AS REINFORCEMENT
FIGURE 1-7 UNREINFORCED DUCT
FIGURE 1-8 CROSSBROKEN DUCT & BEADED DUCT
FIGURE 1-9 DUCT REINFORCED ON TWO SIDES
FIGURE 1-10 DUCT REINFORCED ON ALL SIDES
FIGURE 1-12 DUCT OVER 120" (3048 MM) WIDE
FIGURE 1-15 CORNER CLOSURES - FLANGES
FIGURE 2-22 DUCT LINER INTERRUPTION
TABLE 3-2A ROUND DUCT GAGE UNREINFORCED POSITIVE PRESSURE
TABLE 3-2B ROUND DUCT GAGE NEGATIVE PRESSURE
FIGURE 3-1 SEAMS ROUND DUCT AND FITTINGS
FIG. 3-2 TRANSVERSE JOINTS ROUND DUCT
FIGURE 3-6 FLAT OVAL DUCTS
FIGURE 3-9 FLEXIBLE DUCT SUPPORTS
FIGURE 3-10 FLEXIBLE DUCT SUPPORTS
TABLE 4-1 RECTANGULAR DUCT HANGERS MIN. SIZE
TABLE 4-2 MINIMUM HANGER SIZES FOR ROUND DUCT
FIGURE 4-4 LOWER HANGER ATTACHMENTS
Questions&
Answers