Transitions & Reducers ยท Transitions & Reducers
Rectangular eccentric transition flat on bottom
Maintain bottom elevation
ConnectionFlanged or S-drive
SupportAdjacent supports
Before you start
- Confirm the fitting is flat on bottom and verify why the lower plane must remain fixed.
- Check whether the bottom-flat condition affects drainage, debris, cleanout, or equipment alignment.
- Mark BOTTOM before lifting.
- Inspect both connection ends and the transition body.
Tools and materials
Flat-on-bottom rectangular eccentric transition, approved flange or S-and-drive components, gasket, corners, cleats, fasteners, sealant, level or laser, marker, clamps, and adjacent supports.
Lay it out
- Establish the bottom-of-duct elevation through both adjoining runs.
- Mark the changing top plane.
- Check for prohibited low pockets or collection points.
Set and support it
- Support both adjoining runs before connecting.
- Keep the bottom plane fixed and level.
- Prevent the transition from rolling during fit-up.
Make the connection
- 1
Set and connect the large end to the verified bottom reference.
- 2
Square the transition while holding the bottom plane.
- 3
Align the smaller duct without lifting or dropping the fixed lower plane.
- 4
Complete the second mechanical joint.
- 5
Seal required seams and joints.
- 6
Load supports and verify the bottom line remains straight.
Check the install
- The bottom plane stays straight.
- The fitting does not roll.
- The top changes smoothly.
- No prohibited low pocket is created.
- Both joints remain fully seated and sealed.
Common mistakes
- Installing the fitting flat on top instead.
- Using the transition to correct a vertical offset.
- Allowing one support to raise the small end.
- Ignoring drainage or debris concerns.
Stop and ask
Stop if the bottom-flat orientation creates a drainage, debris, access, or equipment problem, or differs from the approved design.