TinnerFlow
Elbows & Offsets ยท Elbows & Offsets

Rectangular two-piece offset

Obstacle offset

ConnectionFlanged or S-drive
SupportSupports at each change

Before you start

  • Field-measure the actual rise, travel, fitting depth, and available straight length between fixed points.
  • Confirm the offset stays in one plane and does not change duct size unless the approved fitting shows it.
  • Check both direction changes for access, insulation, structure, and hanger clearance.
  • Stage the complete offset assembly and supports before lifting.

Tools and materials

Two-piece rectangular offset assembly, approved flange or S-and-drive components, gasket, fasteners, sealant, level, laser, tape, marker, clamps, and supports near both changes of direction.

Lay it out

  1. Mark the starting and ending centerlines and elevations.
  2. Calculate and verify rise and travel from the actual field condition.
  3. Mark top, bottom, inlet, outlet, and the intended offset plane on the floor.

Set and support it

  1. Install support near each direction change.
  2. Preassemble on the floor when size and access allow.
  3. Lift from more than one point to prevent the center piece from twisting.

Make the connection

  1. 1

    Set the first section and connect the upstream end.

  2. 2

    Align the first change of direction to the marked plane.

  3. 3

    Set the center piece level or to the required pitch.

  4. 4

    Connect the second change of direction.

  5. 5

    Bring the downstream run to the final centerline without springing the assembly.

  6. 6

    Complete all mechanical joints and seal required seams.

  7. 7

    Load the supports and verify the offset remains in one plane.

Check the install

  • The offset matches the measured rise and travel.
  • Both changes lie in one plane.
  • No joint is under spring tension.
  • Clearances and access remain usable.
  • Supports carry the assembly at both changes.

Common mistakes

  • Eyeballing the rise and cutting the center piece short.
  • Flipping one fitting and creating a compound twist.
  • Using the offset to change size unintentionally.
  • Forcing the final joint and leaving the assembly stressed.

Stop and ask

Stop if the offset changes system size, blocks access, cannot stay in one plane, or the field dimensions do not match the fabricated assembly.