Field-measured custom transition

Before you start

• Measure all four planes, both centerlines, offsets, opening sizes, joint types, access clearances, and actual gap before sketching the fitting.
• Determine whether the mismatch is a simple transition, an offset, a compound fitting, or evidence that the route is wrong.
• Do not begin cutting adjacent duct until the fitting and dimensions are approved.
• Check whether the change affects airflow, equipment performance, fire rating, listed assemblies, or service access.

Lay it out

1. Record width, height, diameter, elevation, centerline, rotation, and available fitting length at both ends.
2. Create a dimensioned sketch showing top, bottom, airflow direction, offsets, and joint types.
3. Have the field dimensions and fitting concept reviewed before fabrication.

Set and support it

1. Install supports for both adjoining runs and the custom fitting.
2. Do not rely on the custom transition to pull misaligned duct together.
3. Keep the fitting accessible for final adjustment and inspection.

Make the connection

1. 1

   Verify the approved shop drawing or field sketch against the actual opening.

2. 2

   Set the custom fitting on its support.

3. 3

   Connect the controlling end first.

4. 4

   Recheck all planes and centerlines.

5. 5

   Bring the second run to the fitting without forcing it.

6. 6

   Complete the system-specific mechanical joints.

7. 7

   Seal required seams and joints.

8. 8

   Inspect the internal path for abrupt steps, lips, or makeshift piecing.