The flammability and combustibility of non-metallic
duct materials is controlled by NFPA 90A, 90B, and
91. Show the extent of non-metallic duct on the
drawings when these standards limit its use.
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2.6.1
Metal Ductwork
All aspects of metal ductwork construction, including all fittings and
components, shall comply with SMACNA HVAC Duct Const Stds unless otherwise
specified. Elbows shall be radius type with a centerline radius of 1.5
times the width or diameter of the duct where space permits. Otherwise,
elbows having a minimum radius equal to the width or diameter of the duct
or square elbows with factory fabricated turning vanes may be used.
Ductwork shall meet the requirements of Seal Class C. All ductwork in VAV
systems upstream of the VAV boxes shall meet the requirements of Seal Class
A. Sealants shall conform to fire hazard classification specified in
Section 15080 THERMAL INSULATION FOR MECHANICAL SYSTEMS and shall be
suitable for the range of air distribution and ambient temperatures that it
will be exposed to. Do not use pressure sensitive tape as a sealant.
Spiral lock seam duct, and flat oval shall be made with duct sealant and
locked with not less than 3 equally spaced drive screws or other approved
methods indicated in SMACNA HVAC Duct Const Stds. Apply the sealant to the
exposed male part of the fitting collar so that the sealer will be on the
inside of the joint and fully protected by the metal of the duct fitting.
Apply one brush coat of the sealant over the outside of the joint to at
least 50 mm 2 inch band width covering all screw heads and joint gap.
Dents in the male portion of the slip fitting collar will not be
acceptable. Fabricate outdoor air intake ducts and plenums with watertight
soldered or brazed joints and seams.
2.6.1.1
Metallic Flexible Duct
a. Duct shall conform to UL 181 and NFPA 90A with factory-applied
insulation, vapor barrier, and end connections. Fire hazard rating of
duct assembly shall not exceed 25 for flame spread and 50 for smoke
developed. Proved ducts designed for working pressures of 497 Pa (gage)
two inches water gauge positive and 373 Pa (gage) 1.5 inches water
gauge positive. Flexible round duct length shall not exceed 1525 mm
five feet. Secure connections by applying adhesive for 51 mm two inches
over rigid duct, apply flexible duct 51 mm two inches over rigid duct,
apply metal clamp, and provide minimum of three No. 8 sheet metal
screws through clamp and rigid duct.
b. Inner duct core: Flexible core shall be interlocking spiral or
helically corrugated and constructed of zinc-coated steel, aluminum, or
stainless steel; or shall be constructed of inner liner of continous
galvanized spring steel wire helix fused to continuous, fire-retardant,
flexible vapor barrier film, inner duct core.
c. Insulation: Inner duct core shall be insulated with mineral fiber
blanket type flexible insulation, minimum of 25 mm one inch thick.
Insulation shall be covered on exterior with manufacturer's standard
fire retardant vapor barrier jacket for flexible round duct.
2.6.1.2
Insulated Nonmetallic Flexible Duct Runouts
Use flexible duct runouts only where indicated.
Runout length shall be as
SECTION 15895
Page 16
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