Round Branch Clocking: Mark the Tap Direction Before Cutting the Main

Fast answer

Clock the branch from a stable building reference and the actual downstream route before cutting. A branch can be the right size and location but point into structure or another trade.

What to check

1. Confirm the branch station from a control point, not accumulated joint lengths.
2. Mark the main duct centerline and the intended branch direction.
3. Check the branch route, hanger position, insulation, and nearby trades.
4. Set the tap or fitting against the mark and verify the clocking from more than one view.

Do not

Do not cut the opening from a rough eyeball or from a rotated seam without confirming the intended branch direction.

Ask the foreman

“I measured the branch station from the control line and marked the clocking toward the room. Can you verify this angle before I cut the main?”

Why it matters

A misclocked opening is difficult to hide and can force a crooked branch, patched hole, or replacement section.