New Duct Components

Select insulation:

with a flame spread and smoke development index of 25/50 when tested in accordance with ASTM E84 or UL 723 and that includes an exterior vapor retarder layer

Select duct materials:

with a flame spread of no more than 25 when tested in accordance with ASTM E84 or UL 723 and that are UL 181, SMACNA, NAIMA approved or conform to ASTM A653

Remove all old ductwork and duct insulation from the premises

During renovation or construction, block registers, grilles, and diffusers with a durable material

Do not use duct system until construction is finished

For exterior ducts (i.e., exposed to outdoors), use duct material that meets the following criteria:

insulation level of R-12 or greater

includes a weatherproof barrier that is resistant to ultraviolet light damage

will not be damaged by weather

When a 90 degree turn is required in the plenum, use radius elbow fittings or square fittings with turning vanes

Supply plenum must be the same size or larger than the air handler supply opening

If equipment is installed on top of the return plenum, plenum platform must independently support the weight of the equipment

Install reducers between sections of different size ducts in accordance with existing standards based on duct material (e.g., SMACNA, NAIMA)

Install runs as short as possible

Install take-offs onto the trunk in accordance with duct construction standards (SMACNA)

Install take-offs using mechanical fasteners for all applications

Take-offs that create high turbulence will not be used (e.g., elbows with integrated dampers, scoops)

Install flexible duct as straight as possible and fully stretched without unnecessary sagging, crimping, or bends

Do not bend flexible duct more than 45 degrees without using a rigid elbow

Use a rigid connector when joining two pieces of flexible duct together

Use boots with a directional collar (e.g., 45 degree elbow) whenever ducting turns directly after the boot connection

If using straight boots, connect an elbow to the boot before connecting the duct

Do not connect flexible duct directly to a straight boot if it turns more than 15 degrees within 6' of boot connection

Install fire dampers and ductwork in accordance with applicable fire code

Install smoke alarms inside duct plenums that convey more than 2500 cfm

Seal ductwork penetrations through fire rated surfaces according to applicable code requirements for the surface

Install accessible filter grills that have no air bypass around the filters

Install filter slot covers to prevent return air leakage

Avoid filters with high static pressure drop unless system is designed for them

Room-to-room pressure differences shall not exceed 3 pascals with the air handler running

Install appropriate means of pressure balancing if necessary (e.g., transfer grilles, jumper ducts, individual room returns)

Seal all ducts in accordance with SWS Subtopic "Duct Sealing"

Seal ductwork penetrations through interior walls with a durable and compatible sealant (e.g., caulk, silicone)

Fasten duct connections in accordance with SWS detail "Duct Repair: Mechanical Fastening"

Support ducts in accordance with SWS detail "Duct Repair: Duct Support"

Insulated ducts in accordance with SWS Detail "General Duct Insulation"

Install dampers as close to the trunk as possible and in accessible locations to the fullest extent possible