What Size Notes an Elbow, Offset, or Transition Needs

When a rectangular fitting line only shows one size, the shop still has to ask what the other end is, how far it offsets, or which way it faces. That slows the quote. This article covers the size notes an elbow, offset, or transition usually needs before it can be fabricated - so you can mark them once and send a cleaner package.

For the full quote checklist (drawings, materials, connections, releases, pickup or delivery), see the Contractor Guide. For rectangular fabrication itself - straight sections, fittings, and how to request an estimate - see Rectangular Duct. This post stays on fitting dimensions only.

DuctAxis is a commercial duct fabricator in Clewiston, Florida. We fabricate. We do not install.

Why fitting notes get stuck

Straight duct is often a width x height and a length. Rectangular fittings are different. An elbow turns. An offset shifts the centerline. A transition changes size, and sometimes shape or facing. If any of those moves is missing from the note, the estimator cannot build a ticket without guessing or calling you back.

Common gaps:

One size on a transition or reducer (missing the other end)
An elbow with no angle or no bend plane
An offset with no rise, run, or total shift
No length on a fitting that is not a standard short piece
Facing or orientation left off when the field needs a specific turn
Lined or double-wall size listed without saying inside or outside

You do not have to redraw every fitting. A clear schedule line or a dimensioned sketch with the notes below is enough to start estimating. Free estimates and takeoffs are available when the set is thin; clearer notes still cut questions.

What to put on every rectangular fitting line

Before the fitting-specific notes, make these consistent across elbows, offsets, and transitions:

Mark or tag that matches the plan.
Quantity (piece count, and any "typical of" multipliers spelled out).
Both end sizes as width x height, in the same order used on the rest of the set.
Material and construction as shown on the documents (bare, lined, double-wall, and so on). Do not invent a gauge - send what the drawings or specs state.
Connection type at each end if it differs from the run or is called out at equipment.
Inside vs. outside on lined or double-wall work, so the clear opening is not confused with the outside of the assembly.

Final dimensions, materials, and fabrication follow your approved project requirements and are confirmed during estimating.

Elbows: angle, plane, and throat

A rectangular elbow needs more than one duct size.

Sizes

Entering size (width x height)
Leaving size (width x height), even when both ends match - write both so nothing is assumed

Turn

Angle (for example 90 or 45 degrees), or the angle shown on the plan
Plane of the bend - which way the elbow turns relative to the width and height. A note such as "bend in the width" or "bend in the height," or a small sketch with an arrow, prevents the wrong orientation in the field.

Geometry that changes the piece

Throat or centerline radius if the documents call it out, or if the fitting is not a simple short radius piece
Fitting length along the run if the elbow is stretched or includes straight collars on either end
Turning vanes when the schedule or spec requires them - say so on the line and see Turning Vanes for how vanes are handled with the package

If the elbow is mitered, radiused, or built to a special shape, say that in the note or attach the detail. Do not rely on "elbow" alone when the drawing shows a nonstandard turn.

Offsets: how far, how long, which way

An offset moves the duct centerline without necessarily changing size. The shop needs the shift, not only the duct size.

Sizes

Entering size and leaving size (width x height). Write both even when they match.

Offset geometry

Offset distance - how far the centerline moves (rise, run, or total offset as shown on the plan)
Length of the fitting along the duct run, or the available space between clearances
Plane - which direction the offset shifts (for example, right, left, up, or down as viewed on the drawing), or a sketch with the facing marked

When size also changes

If the piece is both an offset and a transition, treat it as both: both end sizes plus the offset distance, length, and facing. Missing either side is a common re-quote trigger.

Complex one-offs belong with a dimensioned sketch. For custom transitions, offsets, and equipment connections as a product scope, see Custom Fittings. Keep sketch-facing detail there; this article only lists the size notes the rectangular schedule needs.

Transitions and reducers: both ends and the length between them

A transition or reducer is defined by the change from one opening to another.

Sizes

Entering size (width x height)
Leaving size (width x height)
Round-to-rectangular or other shape changes: state both shapes and both sizes clearly (for example, round diameter to rectangular width x height)

Length and alignment

Fitting length between the two ends, if the documents or clearance require a specific length
Concentric vs. eccentric (or which sides hold flush) when the alignment matters in the field
Facing when one side must stay against a wall, slab, or equipment

A single size on a transition line almost always means something is missing. If the schedule says "reduce to ..." without the starting size on that line, point back to the upstream mark or write both sizes on the fitting line itself.

Quick checklist before you send the fitting list

Use this against elbows, offsets, and transitions on the rectangular package:

Mark matches the plan
Quantity and any "typical" multipliers are clear
Both end sizes are listed (width x height, consistent order)
Elbow angle and bend plane (or sketch) are noted
Offset distance, length, and direction are noted
Transition length and alignment (concentric/eccentric or flush side) are noted when they matter
Inside vs. outside called out on lined or double-wall fittings
Material / construction per documents (no guessed gauge)
Connections noted when they differ by end or at equipment
Turning vanes or special geometry called out when required
Odd pieces have a dimensioned sketch attached

If a box is empty, either fill it from the drawings or flag it in the request ("offset distance not shown on M-401, need confirmation"). That is faster than an incomplete line that looks complete.

How this fits the rectangular package

Send straight duct and fittings together when you can. The rectangular duct page is where fabrication scope for rectangular work lives - straights, elbows, transitions, offsets, reducers, plenums, and equipment connections built to your schedule. This article does not replace that page; it only helps the fitting notes arrive complete.

When you are ready to price the package, use the Contractor Guide for project details, drawings, construction requirements, dates, and pickup or delivery notes. Free shipping applies anywhere in Florida. Delivery details for other states in the service area are confirmed with your project quote - do not assume free shipping outside Florida.

Send the notes with your request

When the fitting sizes are marked, request a quote. Uploads accept PDF, XLSX, XLS, CSV, DWG, DXF, and ZIP files: up to 8 files, 20 MB each, 50 MB total. For a larger package, call (863) 599-7014 or email office@ductaxis.com.

Quote response time: under 48 hours, excluding weekends. That is how long it takes to get a quote back, not the fabrication lead time.
Shipping: Free shipping anywhere in Florida. Delivery outside Florida is confirmed with your quote.
Shop: 535 E El Paso Avenue, Suite C, Clewiston, FL 33440

Free estimates and takeoffs are available. Send what you have; clearer elbow, offset, and transition notes still make the first pass cleaner.

Dimensions, material grades, and ratings are confirmed during estimating. This article is general guidance for fitting size notes and does not replace your project specifications, drawings, or engineer of record.