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Equipment, Flex & Terminal Connections ยท Equipment & Terminals

Roof curb duct connection

Rooftop unit

ConnectionCurb adapter/flanged joint
SupportStructure/curb framing as designed

Before you start

  • Confirm the exact curb and rooftop-unit model, supply and return opening sizes, orientation, curb adapter, duct support, roofing detail, and installation sequence.
  • Verify which duct sections must be installed before the unit is set.
  • Inspect curb openings, adapter, roofing, gasket, and unit base.
  • Mark supply and return clearly to prevent cross-connection.

Tools and materials

Approved roof curb or curb adapter, supply and return duct sections, flange or adapter hardware, gasket and seal materials, structure supports, roofing protection, level, tape, marker, lift coordination tools, and manufacturer submittals.

Lay it out

  1. Verify curb opening dimensions and orientation against the unit submittal.
  2. Mark supply and return on the curb and duct.
  3. Coordinate service clearances and roofing access.

Set and support it

  1. Support duct from structure or the approved curb framing detail.
  2. Do not let the unit base carry unintended duct load.
  3. Protect the roof membrane during all work.

Make the connection

  1. 1

    Verify the curb is level, square, and correctly oriented.

  2. 2

    Install required duct sections before unit placement.

  3. 3

    Connect and seal supply and return transitions.

  4. 4

    Support both ducts independently.

  5. 5

    Install curb gasket and approved weather-seal components.

  6. 6

    Set the unit without crushing or shifting the duct.

  7. 7

    Inspect openings, seals, and service clearances after setting.

Check the install

  • Supply and return openings align correctly.
  • No cross-connection is present.
  • The unit base does not carry unintended duct weight.
  • The curb and weather seals are complete.
  • Service clearances remain open.

Common mistakes

  • Setting the unit before required duct sections are installed.
  • Reversing supply and return.
  • Using the unit base to support duct.
  • Damaging the roof membrane during installation.

Stop and ask

Stop if the curb and unit model, opening dimensions, supply/return orientation, adapter, or roofing detail do not match.