Transitions & Reducers ยท Transitions & Reducers
Rectangular eccentric transition flat on top
Maintain top elevation
ConnectionFlanged or S-drive
SupportAdjacent supports
Before you start
- Confirm the fitting is flat on top and understand why that top plane must remain fixed.
- Verify large and small sizes, transition length, airflow direction, and both connection types.
- Mark TOP on the fitting before it leaves the floor.
- Check headroom and drainage implications before installation.
Tools and materials
Flat-on-top 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 top-of-duct elevation through both adjoining runs.
- Mark the changing bottom plane.
- Confirm the fitting does not roll or reverse the intended orientation.
Set and support it
- Support both adjoining runs before the connection.
- Hold the transition with its top plane level.
- Place supports so the fitting cannot rotate.
Make the connection
- 1
Set and connect the large end at the verified top elevation.
- 2
Keep the top plane continuous while squaring the transition body.
- 3
Align the smaller duct to the small end.
- 4
Complete the second mechanical joint.
- 5
Seal required joints and seams.
- 6
Load the supports and recheck the top plane from end to end.
Check the install
- The top plane stays level and continuous.
- The bottom changes smoothly.
- The fitting has no twist or roll.
- Both joints are fully seated and sealed.
- Headroom and drainage intent remain intact.
Common mistakes
- Installing the fitting upside down.
- Rotating it to make the small duct reach.
- Checking only the bottom plane.
- Allowing an unsupported run to roll the fitting.
Stop and ask
Stop if the flat-side orientation conflicts with headroom, drainage, equipment alignment, or the approved drawing.