DUCT CONSTRUCTION STANDARDS
ISSUE:
Importance of showing duct pressure classifications on contract drawings.
BACKGROUND:
SMACNA (Sheet Metal and Air Conditioning Contractors' National Association)
HVAC Duct Construction Standards, Metal and Flexible, second edition, 1995,
states, the designer is responsible for determining the pressure class or classes
required for duct construction on a project. The designer must also show specific
pressure classifications on the contract drawings.
SMACNA also states, where no pressure classifications are shown by the
designer, the 250 Pa (1" water gauge) pressure class is the basis of compliance,
regardless of velocity in the duct, except when the duct is variable volume, all
variable volume duct upstream of VAV boxes, the 500 Pa (2" water gauge) is the
basis of compliance. Actual pressures can be much higher than the SMACNA
default values, and if not shown properly on the contract drawings, it can lead to
serious problems of leakage, loss of capacity, and energy waste.
RECOMMENDATIONS/CONCLUSION:
1. SMACNA is an industry standard for duct work and VA master specification
section 15840 specifies this standard for construction.
2. The designer of duct work must comply with SMACNA requirements, and must
show specific pressure classifications, and balancing devices on contract
drawings.
FOR ADDITIONAL INFOR MATION:
Contact Satish Sehgal @ 202-565-5032, Kurt Knight @ 202-565-4980, or Sat Gupta @ 202-565-
5268.
July 2 1997
FM-187C-DA73
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