Equipment, Flex & Terminal Connections ยท Equipment & Terminals
Flex duct to round metal branch
Branch extension
ConnectionClamped/sealed flex-to-metal joint
SupportWide flex straps
Before you start
- Confirm the metal collar diameter, flex size, approved connector method, route, support, and allowed length.
- Inspect the metal collar for sharp edges and the flex core for tears.
- Verify the flex can reach without compression, sag, or a tight bend.
- Stage the approved clamps, seals, and wide supports.
Tools and materials
Insulated flex duct, round metal collar, approved clamp or draw band, inner-core sealant or tape, jacket-seal materials, wide straps, cutter, snips, marker, and edge protection.
Lay it out
- Set the shortest direct route from the metal branch to the terminal.
- Plan support points and bend direction.
- Keep the connection accessible for inspection.
Set and support it
- Support the round metal branch independently.
- Install wide straps that spread the load.
- Keep the flex straight during connection.
Make the connection
- 1
Cut the flex square.
- 2
Pull back jacket and insulation.
- 3
Slide the inner core fully onto the metal collar.
- 4
Secure the core with the approved clamp.
- 5
Seal the air barrier at the inner core.
- 6
Restore the insulation over the joint.
- 7
Seal the outer jacket.
- 8
Support the flex at the required points without pinching it.
Check the install
- The core is fully engaged on the collar.
- The clamp and air seal are complete.
- The insulation and jacket are restored.
- No sag, pinch, or sharp bend remains.
- The metal branch carries no flex-support load beyond the connection.
Common mistakes
- Clamping only the outer jacket.
- Leaving the inner core bunched.
- Using a narrow support that pinches the duct.
- Pulling torn flex onto the collar.
Stop and ask
Stop for a torn core, crushed insulation, damaged jacket, sharp collar edge, or a route that requires excessive bend or sag.