Spiral & Round Duct · Straight Runs & Assembly

Spiral eccentric reducer

Offset size change

ConnectionSlip-fit/gasketed eccentric reducer

SupportAdjacent supports preventing rotation

Before you start

The whole point of an eccentric reducer is the FLAT SIDE.
Before you touch it, find out where the flat is supposed to go and why: flat on top for headroom, flat on the bottom for drainage, flat on a side for a wall clearance.
If the drawing does not say, ask.
Guessing wrong on an eccentric reducer means either a low point that traps water or a duct that hits the deck.
Stage the needed tools and materials before lifting the section: Eccentric reducer, supports on both adjacent runs, sealant or gaskets, fasteners, level, marker..

Eccentric reducer, supports on both adjacent runs, sealant or gaskets, fasteners, level, marker.

Identify the required flat-side orientation. Get it off the drawing or off the foreman, not off a guess.
Mark TOP on the fitting with a marker before it leaves the ground. This is the whole job.

Support both sides so the fitting cannot rotate under load.
Use the approved support method for this condition: Adjacent supports preventing rotation.

1
Connect the large end.
2
Rotate to bring the flat to its marked position and confirm it against the mark.
3
Align the small-end run.
4
Connect the small end.

Flat side in the specified position. Confirm against the drawing, not against memory.
No roll; the fitting is held against rotation by the supports.
Downstream duct aligned, no sideways step.
No low-point trap where one is prohibited.

Installing it flat-side-wrong. If drainage was the reason, you just built a water trap. If headroom was the reason, you just lost your ceiling.
Not marking the top on the ground, then trying to figure out orientation on a ladder with the fitting half in.
Letting the fitting roll after connection because neither side is supported against rotation.

Stop if orientation affects drainage, headroom or equipment connection and is not shown