Mirrored Offset: Verify Left-Hand and Right-Hand Before Installation

Fast answer

Compare the offset to the airflow direction, plan view, elevation, and the direction you will be looking before it leaves the ground. A fitting can have the right rise and run and still be mirrored.

What to check

1. Mark upstream and downstream on the fitting and adjoining duct.
2. Stand on the same viewing side used by the shop drawing or field sketch.
3. Confirm which way the offset moves in plan and which way it moves vertically.
4. Dry-check the connector ends and clearance before raising it.

Do not

Do not call an offset correct only because the overall dimensions match; left-hand and right-hand orientation can still be wrong.

Ask the foreman

“I matched the rise and run, marked upstream, and checked the plan-view direction. This offset still moves opposite the coordinated route—do you want it remade or is the drawing view reversed?”

Why it matters

Catching a mirrored offset on the floor prevents a wasted lift and a replacement fitting made from the same bad orientation.