1. HVAC Duct Construction
Bob Wasilewski
Project Manager, Technical Resources
SMACNA

2. HVAC Duct Construction
Standards
WHAT?
WHY?
HOW?

3. Today's Program
1st – 2nd Edition HVAC-DCS
Review Joints and Limitations
Transverse Joints & Reinforcements
Use of the Pressure Class Tables
Tie Rod Addendum

4. Documents Preceding 2nd Edition
HVAC-DCS
Low Velocity Systems Duct Manual
– First Edition 1959
– Second Edition 1963
– Third Edition 1967
Low Velocity Duct Construction Standard
– 1969

5. Documents Preceding 2nd Edition
HVAC-DCS
Low Pressure Duct Construction Standard
– Fifth Edition 1976
High Velocity Duct Systems Manual
– First Edition 1965
High Velocity Duct Construction Standards
– Second Edition 1969

6. Documents Preceding 2nd Edition
HVAC-DCS
High Pressure Duct Construction Standards
– Third Edition 1975
Duct Liner Application Standard
– First Edition 1971
– Second Edition 1975

7. Documents Preceding 2nd Edition
HVAC-DCS
Flexible Duct Installation Standards
– First Edition 1979
– Second Edition 1980
HVAC Duct Construction Standards --
Metal and Flexible
– First Edition 1985

8. Major Changes from First Edition
GENERAL
Text edited to be more reader-friendly
Reading aids added
Static pressure only as the basis for duct
construction classification -- velocity
levels deleted (Table 1-1)

9. Major Changes from First Edition
Chapter 7 revised to facilitate use for
equivalent and comparable tests and ratings
Model project specification added
Reminders to designers to show all required
fire, smoke, radiation and volume control
dampers on contract drawings are accented

10. Major Changes from First Edition
Boiler breeching omitted
Volume damper construction is more
specific
Lead radiation shielding added
Metrics are included
Air terminal runouts and supports are
revised

11. Major Changes from First Edition
RECTANGULAR DUCT REVISIONS
Negative pressure construction given for
4", 6", and 10" w.g.
Six feet reinforcement schedules added
Reinforcement schedules extended to 120"
width

12. Major Changes from First Edition
Tie rod alternatives expanded for both
positive and negative pressures
TDC and TDF joint systems included and
rated as T-25a and T-25b joints
T-24a joint added as a modification of T-24

13. Major Changes from First Edition
Use of 26 gage added for 4", 6" and 10"
pressures
Trapeze hanger tables expanded to cover
the 120" width range
Duct liner pin schedule adjusted
Infrequently used joints (T-4, 8, 17, 18,
19, 20 and 23) omitted

14. Major Changes from First Edition
Round, Flexible and Oval Duct Revisions
Duct pressure classes revised to be positive
and negative at 2", 4" and 10" w.g.
Crimped joint connection length changed
from 1" to 2"
Rectangular branch taps into round added
for straight or 45 degree lead-in-entry

15. Major Changes from First Edition
Type 1 reinforcement of oval duct now has
an internal tie rod (based on ASHRAE test
program)
Maximum support spacing for round
flexible duct and connector changed from
10 feet to 5 feet
Additional riser support details are
provided

16. DUCT SYSTEMS
SIZINGS FIRE/SMOKE CODE
FITTINGS, ETC. PROTECTION COMPLIANCE
CODE
DUCT COMPLIANCE
CONSTRUCTION
SMACNA
HVAC-DCS
2ND ED. 1995
INSPECTION CODE
COMPLIANCE

17. DUCT SYSTEMS
ENGINEER CONTRACTOR
Design Considerations: Construction Considerations:
CFM Panel Thickness (Gage)
Static Pressure Pressure Class (as specified)
Duct Size Panel Width/Height
Fitting Type Joint Type/Spacing
Construction Pressure Intermediate Reinforcement
Class Type/Spacing

18. DEPENDENT VARIABLES

19. REGULAR DUCTS
Maximum Deflection Maximum Test
Pressure
Joint and Reinf. Sheet: Lab:
1/4" on 48" w. 3/8" on 12" Dn. Class Rating + 50%
W/200 on 1/2" on 13"-18"
49"-120" 5/8"on 19"-24" Field:
3/4" on 25"-84" Class Rating + 25%
1" on 85"-120"
Tolerance: Tolerance:
+7.5% +10%

20. Duct Systems
Used for the movement of air in
HVAC/Exhaust systems
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

21. Duct Systems (Continued)
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

23. TABLE 1-2
STANDARD DUCT SEALING REQUIREMENTS

37. EXAMPLE 1
Duct Size 24" x 24"
Pressure Class 2" w.g.
Sheet Stock
Joints/Reinforcements 8 ft / 4 ft
Standing S

40. EXAMPLE 2
Duct Size 42" x 24"
Pressure Class 3" w.g.
5 ft Coil Line
Joints/Reinforcements 5 ft / 2 ½ ft
TDC or TDF

44. MIDPANEL TIE ROD (MPT)
½" w.g. - 6" w.g.
37" - 96"
Duct Dimension
Rectangular Duct

45. Mid Panel Tie Rod Addendum
Joints – All
Tie Rods – Threaded Rod or
Tubing/Conduit with Threaded Insert
Additional Application Tables,
Qualifications and Reader Aids Included

51. FIGURE 1-3 TIE ROD ATTACHMENTS

52. FIGURE 1-4 TRANSVERSE (GIRTH) JOINTS

53. FIGURE 1-4 TRANSVERSE (GIRTH) JOINTS

54. FIGURE 1-4A SPECIAL JOINT PROFILES

55. FIGURE 1-5 LONGITUDINAL SEAMS –
RECTANGULAR DUCT

56. TABLE 1-24 UNREINFORCED DUCT (WALL THICKNESS)

57. TABLE 1-25
T-1 FLAT DRIVE ACCEPTED AS REINFORCEMENT

58. FIGURE 1-7 UNREINFORCED DUCT

59. FIGURE 1-8 CROSSBROKEN DUCT & BEADED DUCT

60. FIGURE 1-9 DUCT REINFORCED ON TWO SIDES

61. FIGURE 1-10 DUCT REINFORCED ON ALL SIDES

62. FIGURE 1-12 DUCT OVER 120" (3048 MM) WIDE

63. FIGURE 1-15 CORNER CLOSURES - FLANGES

64. FIGURE 2-22 DUCT LINER INTERRUPTION

65. TABLE 3-2A ROUND DUCT GAGE UNREINFORCED POSITIVE
PRESSURE

66. TABLE 3-2B ROUND DUCT GAGE NEGATIVE PRESSURE

67. FIGURE 3-1 SEAMS – ROUND DUCT AND FITTINGS

68. FIG. 3-2 TRANSVERSE JOINTS – ROUND DUCT

69. FIGURE 3-6 FLAT OVAL DUCTS

70. FIGURE 3-9 FLEXIBLE DUCT SUPPORTS

71. FIGURE 3-10 FLEXIBLE DUCT SUPPORTS

72. TABLE 4-1 RECTANGULAR DUCT HANGERS MIN. SIZE

73. TABLE 4-2 MINIMUM HANGER SIZES FOR ROUND DUCT

74. FIGURE 4-4 LOWER HANGER ATTACHMENTS

75. Questions
&
Answers