Revit flex duct tag: how to tag flex ducts with size and length

A flex duct runs from a rigid branch to a diffuser. It bends, it often crosses other ducts, and it is the last element the reader checks on a ceiling plan. Revit tags it with its own tag category, so the duct tag you already use does nothing here.

This guide takes the job in order. You load the tag, place it, decide what it shows, and deal with the bends. Each step also shows where the job drags and what RayCAD, a Revit plugin for MEPF tagging, does about it.

What do you need before you tag a flex duct?

• A view that shows flex ducts. A floor plan or ceiling plan with the Flex Ducts category visible in Visibility/Graphics (VG).
• A loaded flex duct tag. The category is called Flex Duct Tags.
• Flex duct tags turned on in the view. Check the Annotation Categories tab in VG and the view template.

How do you tag a flex duct in Revit?

1. Load a flex duct tag

1. Go to the Annotate tab and open the drop-down arrow on the Tag panel.
2. Choose Loaded Tags and Symbols.
3. Click Load and browse to a flex duct tag. If your firm has none, copy a duct tag, open it in the Family Editor, and set the family category to Flex Duct Tags.
4. Check that the tag name now appears next to Flex Duct Tags, then click OK.

The last tag you load for a category becomes the default. Load your firm's tag last.

2. Tag one flex duct with Tag by Category

1. Open the plan.
2. Go to Annotate, Tag, Tag by Category, or type TG.
3. Set the orientation, and turn the leader on or off, on the Properties palette or the Modify | Tag tab.
4. Click the flex duct. The tag appears.
5. Drag the tag to move it. Press Esc twice to leave the command.

Click near the air terminal end. Readers look there first, and the middle of a flex run is usually bent and crowded.

3. Tag every flex duct with Tag All Not Tagged

1. Open the view. Select the flex ducts you want tagged, or select nothing to tag all of them.
2. Go to Annotate, Tag, Tag All.
3. Choose All objects in current view or Only selected objects in current view.
4. Select Flex Duct Tags.
5. Set Leader, Leader Length, and Tag Orientation, then click OK.

Tag All skips ducts that already have a tag, and it runs on the active view only.

How do you change what a flex duct tag shows?

A flex duct has a diameter, a length, a flow, and a system. To add the length to a tag:

1. Select a flex duct tag and click Edit Family.
2. Save a copy under a new name.
3. Select the label and click Edit Label.
4. Add Length from the list of parameters. Add Diameter if the tag does not show it. Use Break to put a value on its own line.
5. Select Length and click the format button. Clear Use project settings and set the units and rounding if the sheet needs a different format from the schedule.
6. Click Load into Project.
7. Select the flex ducts and pick the new type in the Type Selector.

Can you trust the flex duct length?

Check it before you issue a sheet. Revit calculates a flex duct's length from its path, and users report that the result near a bend can differ from the length you would measure along the duct. A flex run in a tight ceiling space is where the difference shows.

1. Select the flex duct and read Length in the Properties palette.
2. Measure the drawn path with the Measure tool, along the bends.
3. If the two differ by more than your tolerance, decide which number the sheet should show and note it.

Many standards and local codes also limit the length of a flex connection, so a tag with a length on it gets read closely. Check the limit in your specification.

How do you handle a flex duct that bends or crosses other ducts?

The tag belongs on the part of the flex duct the reader can see.

• Keep the tag on a straight stretch. A tag on a bend sits across the curve and reads as part of the line.
• Use a leader when the flex is short. A tag on a 600 mm flex covers it. A leader moves the text to open ceiling.
• Keep the tag off the rigid duct above it. Flex ducts often run under a larger duct. A tag on the overlap labels the wrong element at a glance.

What goes wrong with flex duct tags?

What else breaks when you tag flex ducts by hand?

Missed ducts. Flex ducts are short and numerous, and a missed one is easy to overlook until the contractor asks for the size. RayCAD puts every duct it could not place in a list, with the reason, and takes you to each one. See how that reduces RFIs.

Model changes. When a terminal moves, the flex duct reroutes and its tag stays where it was. Select those ducts and RayCAD's Retag tool tags them again with the same settings.

How does RayCAD tag flex ducts end to end?

You pick the views. RayCAD finds every round flex duct, decides where its tag goes, places it, and lists anything it could not place. You review the result. Click-saver tools shorten each click but leave every decision and every placement to you.

RayCAD tags flex ducts with size, length, and system abbreviation. It places the tag along the flex path and near the air terminal end, and it reads the values from the duct. It tags the rigid ducts, fittings, accessories, air terminals, and equipment on the same run in the same pass.

What should you check before you issue the sheet?

• Every flex duct has a tag, or a note says why not.
• Diameters match the air terminal schedule and the rigid branch they connect to.
• Lengths match the path, and no flex run is above the limit in your specification.
• No tag covers a diffuser, a light, or another tag.

Every version from Revit 2021 to 2027 is supported. Try RayCAD, or email us to book a demo. The guide to tagging ducts covers the rigid ducts these flex runs connect to.

What building a flex duct tagging script yourself really costs

• Time. Whoever builds and maintains the script is doing software development instead of the billable engineering and drafting work they were hired for.
• The AI loop.With Claude or ChatGPT it becomes an endless loop of “fix this”, “now fix that”. Each fix can break a case that worked before, and nobody on the team owns the code.
• Cost. Hours spent building and maintaining scripts, times your hourly rate, against $200 per month for RayCAD for the whole company.

You can build a flex duct tagging script, and this page shows how. For production MEPF sheets, RayCAD is the cheaper and safer choice. Try it free for 15 days.