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

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