I get calls every week from field techs ordering transitions. Good techs. Experienced techs. Guys who have been doing this a long time. And a lot of those calls end the same way: I have to call them back because I still don’t have enough information to build the piece.
That is not a knock on the field. It is just a communication problem, and it burns time on both ends. The shop has to stop what it’s doing, track somebody down, wait on a return call, and then restart the order. The tech has to go back and get measurements he thought he already had. Meanwhile the job sits there.
It is avoidable.
What a Transition Actually Is
A transition is just a fitting that changes from one duct size to another. Maybe both dimensions change, like 24x12 to 16x10. Maybe only one changes, like 24x12 to 24x8. It might be centered. It might be offset. It might move in two directions at once.
A lot of confusion starts right there, because guys in the field will sometimes use the word “transition” loosely and mean a few different things. Before you start rattling off numbers, make sure you and the fabricator are talking about the same fitting.
The Numbers You Need
1. The starting size. Give the size of the larger, or incoming, end.
For a vertical application, the width is left to right and the depth is front to back.
For a horizontal application, the width is up and down and the depth is front to back.
Do not guess. If you are tying into existing duct in the field, measure what is actually there.
2. The ending size. Give the size of the smaller, or outgoing, end using the same orientation.
If you switch how you are describing the piece halfway through the call, you are asking for trouble.
3. The length. How long does the transition need to be?
A lot of techs treat length like a throwaway number, but it matters. A short transition makes for a steeper taper. That can mean more turbulence and more pressure loss. Sometimes the job gives you no choice, and that is fine, but the shop still needs the number.
4. The offset. Is it centered, or is one end shifted?
This is the one that gets missed all the time. A transition can be dead center, offset left or right, offset front or back, or offset both ways. If the two openings are not lined up, the shop needs to know exactly how far they are off and in which direction.
5. The connection type. How does each end connect?
Slip and drive? Raw? Flanged? What gauge? The shop cannot finish the fitting correctly if it does not know how the piece is supposed to tie in.
The One That Gets Missed Most
Offset is the one that causes the most trouble.
A tech will have both end sizes. He will have the length. He will know what kind of connection he wants. But what he actually needs is an offset transition, and what gets ordered is a centered one. Those are not the same fitting. You cannot treat them like they are.
That is where callbacks happen. That is where time gets wasted.
If you are not sure whether the piece is centered or offset, send a quick sketch or a couple photos with the measurements. That clears up a lot of problems before they start.
A Note on Orientation
This is where people get twisted up.
For a vertical transition, think of the face of the duct in front of you. Width runs left to right. Depth runs front to back.
For a horizontal transition, width changes to up and down, while depth is still front to back.
The important part is not the label by itself. The important part is that you stay consistent and make it clear how you are looking at the piece.
If there is any chance of confusion, stop and sketch it.
The Fastest Way to Order One
If you want the shop to build it right the first time, have these ready before you call:
- starting size
- ending size
- length
- offset direction and amount
- connection type and gauge
- a quick sketch if the fitting is anything but obvious
That is it.
Clean information in, clean fitting out, and the job keeps moving.
K & E Sheet Metal has a mobile-friendly transition request form with a real-time 2D drawing that updates as you enter dimensions. Worth saving if you order these in the field.