Division of Administration and Finance | Planning + Design + Construction Construction Standards
Ductwork (Non-Lab) | 233100
The following information shall be included in specifications prepared for use on all University of Cincinnati projects. This
information is supplemental and not intended to be a complete specification.
PART 1 GENERAL
1.01 General Criteria
General - This Standard Section contains the requirements specific to the design and selection of
supply air, return air, and exhaust air ductwork and accessories. The following requirements are of a
general nature and apply to all University of Cincinnati renovation and new construction projects. The
University has more specific design standards that apply to particular building and space usage. The
designer shall include the requirements in this general standard and all specific standards that apply
the project. If there are any conflicts between the general and the specific standards, the specific,
standards shall supersede.
Duct Layout - Size and configure duct systems to minimize the total fan pressure required and
accommodate the acoustical requirements discussed in this standard. Size and configure duct and fan
systems, that exhaust or relieve air to the outside or bring in air from the outside, to ensure enough total
system pressure to minimize wind-assisted and wind-opposed effects on air balance stability.
Unfiltered Air Streams- Do not install devices or obstructions in unfiltered air streams that have the
potential to collect dust, lint, or other particulate matter. These devices include but are not limited to the
following:
Turning vanes
Splitter dampers
Air extractors
Equalizing grids
Screens
Perforated plates
Do not install turning vanes in return or exhaust ducts. Obtain prior approval prior to designing negative
pressure duct systems containing short radius elbows with splitter vanes.
Rectangular Supply Duct Elbows - Use standard radius elbows wherever possible. If available space will
not allow standard radius elbows use mitered elbows with turning vanes.
Round & Oval Supply Duct Elbows - Use standard radius elbows wherever possible. If available space
will not allow standard radius elbows, R/D value may be reduced, as long as the design engineer accounts
for acoustical, pressure, and downstream turbulence issues caused by the elbow. In no case, shall the R/D
value be lower than 0.75.
Return Duct Elbows – Use radius elbows wherever existing space will allow. If space will not allow the use
of radius elbows, mitered elbows may be used as long as the design engineer accounts for acoustical,
pressure, and downstream turbulence issues caused by the elbow.
Access - Provide access to the interior of ductwork at all locations that require testing, inspection,
maintenance, or cleaning. These locations include but are not limited to:
Fire and smoke dampers
Turning vanes
Reheat coils and electric duct heaters
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Division of Administration and Finance | Planning + Design + Construction Construction Standards
Show all duct access panels and doors on the drawings. Coordinate all duct access locations with the
Architect. Verify the provision of ceiling or wall access at every location of duct access. All duct access
doors shall open against duct air pressure.
1.02 Performance Requirements
Standards - This standard section applies to the following AIA/CSI sections:
23 31 13 Metal Ducts
23 31 16 Nonmetal Ducts
23 31 19 HVAC Casings
23 30 00 Air Duct Accessories
Duct Pressure Class - Indicate duct pressure classes on the drawings. The duct pressure class for all
systems shall meet or exceed the maximum anticipated pressure in each section of ductwork and be no
lower than 1” water gauge or any of the values stated below.
System Malfunctions - The duct pressure class shall accommodate system malfunctions such as a closed
terminal or fire damper that would cause the fan to work against a near dead head. The design of alternative
methods to accommodate system malfunction, such as pressure relief devices, must receive prior approval.
Variable Volume Systems - Design the entire supply air duct system, upstream of the terminal units, to be
at the same pressure class. This class shall meet or exceed the maximum required pressure, and shall not
be less than 3” water gauge. Ductwork downstream of variable volume terminals shall have a pressure
class that will accommodate the maximum design airflow of the terminal, and shall not be less than 1” water
gauge.
Acoustical Requirements - Design duct systems to accommodate the NC or RC levels of the spaces
served by, penetrated by, and adjacent to the duct systems. Flexible duct shall not be installed anywhere in
the high-pressure side of any Variable Air Volume system (upstream of the terminal units). This includes the
inlets to VAV boxes. Size ductwork so air velocity does not exceed 2700 fpm.
Plenum Materials - All materials installed in supply air plenums, return air plenums, or mechanical rooms
used as supply or return air plenums shall have a 25/50 flame spread and smoke developed rating as per
ASTM E-84.
1.03 Product Coordination
Existing Conditions - This standard section, “Non-Laboratory Ductwork and Accessories” contains
the requirements specific to the design and selection of supply air, return air, and exhaust air ductwork
and accessories. The design engineer shall field verify the sizes, quantities, locations, and conditions of all
existing ductwork and duct accessories that will be affected by the project. Perform this verification prior to
the commencement of design. On renovation projects, obtain the existing supply, return, and exhaust air
quantities affected by the renovation. Incorporate these quantities into the new design, where appropriate.
1.04 Sustainability Requirements
(No Standards for this Section)
PART 2 PRODUCTS
2.01 Product Manufacturers
(No Standards for this Section)
2.02 Product Requirements
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Division of Administration and Finance | Planning + Design + Construction Construction Standards
Duct Material - Lock forming quality galvanized steel as per SMACNA. Ductwork shall be rectangular,
round spiral, or oval spiral. The design of duct systems composed of materials other than galvanized steel
must be pre-approved. Non-metallic ductwork passing thru partitions or floors must be Factory Mutual
approved for fire rated separation penetration.
Below Grade Ducts - If below grade ducts cannot be avoided, obtain prior approval for below grade design
and obtain prior approval for the duct material. Below grade ducts must have provisions for drainage.
Material that may be accepted include:
Fiberglass reinforced plastic (FRP)
Vinyl chloride coated steel.
Stainless steel
2.03 Product Accessories
Duct Liner - Do not use duct liner in supply, return or exhaust ductwork. If sound attenuation is required in
the duct system, employ other design methods. Liners for equipment shall be fiber free. Attenuating transfer
elbows and fittings in return air plenums shall utilize fiber free duct liner. All duct and equipment liner shall
meet 25/50 flame spread and smoke developed rating as per ASTM E-84.
Ductwork Sealant & Gaskets - Use water based joint and seam sealant for seams and non-gasketed
joints. Flange gaskets shall be Butyl rubber, neoprene, or EPDM with polyisobutylene plasticizer. Duct tape
shall not be used on any mechanical system for any purpose.
2.04 Product Coordination
(No Standards for this Section)
PART 3 EXECUTION
3.01 Preparation & Coordination
(No Standards for this Section)
3.02 Construction & Installation
(No Standards for this Section)
3.03 Testing & Commissioning
(No Standards for this Section)
3.04 Duct Schedule
See the attached Ductwork Schedule for Non-Laboratory Ductwork.
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Division of Administration and Finance | Planning + Design + Construction Construction Standards
DUCT SEAL CLASS / MAXIMUM LEAKAGE CLASS (CL)
DUCT PRESSURE
NON-LABORATORY DUCTWORK ≤2"
CLASS
3" ≥4"
B/ B/
INTERIOR RECTANGULAR A/6
12 12
ROUND / OVAL B/ B/
SUPPLY, RETURN, RELIEF, & A/6
LONGITUDINAL SEAM 12 12
NEGATIVE PRESSURE
ROUND / OVAL C/
EXHAUST B/6 A/3
SPIRAL SEAM 12
EXTERIOR RECTANGULAR A/6 A/6 A/6
ROUND / OVAL
A/3 A/3 A/3
SUPPLY, RETURN, RELIEF, & LONGITUDINAL SEAM
NEGATIVE PRESSURE ROUND / OVAL
A/3 A/3 A/3
EXHAUST SPIRAL SEAM
RECTANGULAR A/6 A/6 A/6
POSITIVE PRESSURE ROUND / OVAL
A/3 A/3 A/3
PORTION OF EXHAUST LONGITUDINAL SEAM
DUCTWORK ROUND / OVAL
A/3 A/3 A/3
SPIRAL SEAM
NOTES:
SEAL CLASS C REQUIRES THE SEALING OF ALL TRANSVERSE JOINTS
SEAL CLASS B REQUIRES THE SEALING OF ALL SEAMS AND JOINTS
SEAL CLASS A REQUIRES THE SEALING OF ALL SEAMS, JOINTS, AND
PENETRATIONS OF DUCTWORK.
MAXIMUM LEAKAGE CLASS IS THE MAXIMUM ALLOWABLE AIR LEAKAGE
(cfm / 100 sq. ft.) AT 1” W.G. DUCT STATIC PRESSURE. {CL = (cfm / 100 sq.
ft.) / (SP)0.65 }
This table is derived from Table 5-2 of HVAC Systems Duct Design, SMACNA –
1990
Tabulated values are not identical to the published SMACNA values.
--- END OF SECTION ---
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