Transitions & Reducers ยท Transitions & Reducers
Rectangular-to-round transition
Equipment/branch connection
ConnectionTDC/TDF to slip/gasketed round
SupportIndependent support
Before you start
- Confirm the rectangular size, round diameter, transition length, airflow direction, round collar orientation, and both joint systems.
- Inspect the rectangular flange, round end, body seams, and roundness.
- Field-check the rectangular centerline and the round centerline.
- Verify the fitting is not being used to correct an unapproved offset.
Tools and materials
Rectangular-to-round transition, approved rectangular joint components, approved round slip or gasketed components, fasteners, sealant, clamps, drift pins, level, laser, and independent support.
Lay it out
- Mark the rectangular top, bottom, and centerline.
- Mark the round centerline and seam clock.
- Confirm the round end is concentric or offset exactly as shown.
Set and support it
- Support the fitting independently.
- Support both adjoining runs.
- Hold the round end against roll.
Make the connection
- 1
Set and connect the rectangular end square.
- 2
Recheck the transition body and round-end centerline.
- 3
Bring the round duct to the fitting without twisting the body.
- 4
Seat the round connection fully.
- 5
Install approved mechanical fasteners.
- 6
Seal both joint systems using the correct method for each.
- 7
Load supports and verify the round end remains round.
Check the install
- The rectangular end is square.
- The round end remains round and correctly centered.
- The transition body is not twisted.
- Both joint systems are fully seated and sealed.
- The fitting has independent support.
Common mistakes
- Treating the round end like it can be rotated anywhere.
- Using the transition to hide a collar-size mismatch.
- Pulling the round duct sideways into the fitting.
- Applying one joint method to both ends.
Stop and ask
Stop if the field opening, round collar size, rectangular size, offset, or joint system does not match the approved fitting.