How to set up a duct size tag in Revit: format, flow, and system

A duct size tag is a small label with a lot of settings behind it. The text comes from the duct, the format comes from three places in Revit, and the placement comes from you. This guide takes them in that order, so you can fix the one that is wrong.

RayCAD is a Revit plugin that places duct and pipe tags for you. Under each step you will see where it slows down on a real project and what RayCAD does at that point.

What does a duct size tag read?

A duct has a Size parameter. A rectangular duct reads width and height, a round duct reads its diameter, and an oval duct reads its two dimensions. The tag label shows that value, plus anything else you add, such as Flow or System Abbreviation.

Revit ships duct size tags in the Annotations folder of its library, under Mechanical. To load one, open the drop-down arrow on the Tag panel of the Annotate tab, choose Loaded Tags and Symbols, and click Load. The full steps for placing it are in the guide to tagging ducts.

How do you change how the size is written?

x Three settings control it. Start with the one that matches the change you want.

1. Change the symbols in Mechanical Settings

1. Go to the Manage tab, then MEP Settings, then Mechanical Settings.
2. Open Duct Settings.
3. Set the symbol between width and height on a rectangular duct, such as x or a spaced x.
4. Set the prefix and suffix for round and oval sizes, such as a diameter symbol before a round size.
5. Click OK.

These symbols apply to every duct size in the project, in tags and in schedules.

2. Change the units and the rounding in Project Units

1. Go to Manage, then Project Units.
2. Choose the HVAC discipline and open the format for Duct Size.
3. Set the units, the rounding, and the unit symbol.
4. Click OK.

Round to the nearest 5 or 10 mm if your standard writes 600 instead of 603. Unit-format rounding goes to the nearest increment, so it does not always round down.

3. Change the format for one tag only

1. Select the tag and click Edit Family.
2. Select the label and click Edit Label.
3. The Size value follows the project settings. To format it for this tag only, build the label from the dimensions instead. Use Width and Height, or Diameter for a round duct.
4. Select each dimension and click the format button next to it.
5. Clear Use project settings.
6. Set the units, the rounding, and the unit symbol, then click OK.
7. Click Load into Project.

This changes that tag family only, and the project settings stay as they are. A tag built from separate dimensions needs one family per duct shape.

How do you add flow to a duct size tag?

1. Select a duct size tag in the model.
2. Click Edit Family on the ribbon.
3. Save a copy under a new name, so the original stays intact.
4. Select the label and click Edit Label.
5. Add Flow from the list of parameters.
6. Use Break if you want the flow on its own line, and set the unit format of the Flow parameter to match your sheets.
7. Click Load into Project, then select the ducts and pick the new type in the Type Selector.

Flow comes from the system calculation. If a tag shows zero, check that the duct system is fully connected and that an air terminal family has its flow parameter linked to its connector.

How do you add the system to a duct size tag?

1. Edit the tag family and open Edit Label.
2. Add System Abbreviation or System Name.
3. Load the family into the project.

The abbreviation is a value you set on the duct system type, in its type properties. Set it once per system type, or the label stays empty.

How do you keep duct size tags readable on a busy sheet?

A size tag is only useful if the reader finds it in a second. These habits do most of the work.

• Keep the text short. Drop units and symbols the sheet already states in a note. A tag that reads 600x300 beats one that reads 600 mm x 300 mm.
• Tag where the size changes. Put one tag at the start of a run and one after each transition. A tag on every segment hides the ducts under text.
• Keep tags horizontal. Rotated text takes longer to read. See the section on angled ducts in the duct tagging guide.
• Use a leader on narrow ducts. A tag on top of a narrow duct covers the linework. A wide duct can carry its tag.
• Keep tags off fittings and off each other. Move them by hand until nothing touches.
• Match the text size to the scale. The text type of the tag family sets the printed size, so check it when you change the view scale.

What goes wrong with duct size tags?

How does RayCAD place duct size tags?

You pick the views. RayCAD reads the model, decides where size tags belong, places them, and lists anything it could not place for you to review. A click-saver plugin speeds up the clicks, and the decisions and placement stay with you. RayCAD takes that work, and you review the result.

It tags rectangular, round, oval, and flex ducts, native and fabrication, on floor plans and section views. It puts a size tag inside a duct when it fits and outside, above or below, when it does not. A duct tag rules profile decides what happens at a size change, and a minimum duct length keeps short stubs clean.

Want to see it on your sheets? Try RayCAD free for 15 days on Revit 2021 to 2027, or email us for a walkthrough. Terms on this page are defined in the MEP tagging glossary.