On a CAD drawing a duct run is two parallel lines, elbows and tees drawn by hand, and a flex connection is a wavy block from the library. Change one size and you redraw a dozen lines. Revit works the other way round: you draw a centreline, the software builds the duct, drops in the elbows, tees and transitions, and keeps the run connected to the equipment.
This article does one job: how to draw ducts in revit 2027 for an apartment, from a concealed fan coil unit to three supply diffusers joined with flex duct. Fourteen steps, each one saying what to click and what appears. To learn the whole HVAC workflow on one sample building, see the Institute's Revit MEP course.
What a revit duct is that a CAD line is not
A duct in Revit carries a duct type, a size, an elevation and a system. An air terminal in Revit does the same for airflow. Autodesk's Draw Duct in a Plan View page says that for two-line duct "Transitions, tees, and elbows are automatically added". Placeholder duct, drawn with the Duct Placeholder tool, carries the same data but no fittings.
Because the duct belongs to a system, the airflow of the diffusers adds up back to the equipment. Where ductwork sits among the three MEP disciplines is covered in what Revit MEP is. That is what later lets Revit size the duct and report pressure loss, the subject of sizing ducts in Revit.
Every duct command sits on the Systems tab, in the HVAC and Mechanical panels.
| Tool | Ribbon | Shortcut |
|---|---|---|
| Duct | Systems › HVAC › Duct | DT |
| Flex duct | Systems › HVAC › Flex Duct | FD |
| Air terminal | Systems › HVAC › Air Terminal | AT |
| Equipment (fan coil, AHU) | Systems › Mechanical › Mechanical Equipment | ME |
| Fitting placed by hand | Systems › HVAC › Duct Fitting | DF |
Prepare the file you can follow along in
The article works in the practice file built in Revit MEP sample files: a copy of the Institute's metric HVAC template file with the Snowdon Towers architectural model linked in, levels copied and floor plan L3 created. That floor is residential; we work in the north apartment between grids D and E.
The Institute's file already carries the fan coil family HVAC-Equipment-FCU (Daikin 3.6 kW and 7.1 kW), the supply grille HVAC-AirTerminal-SAG at 600 × 600 and rectangular duct types named after the flange joints used on Vietnamese sites: C, V, TDC. With another template, substitute the equivalent families and duct types.
How to draw ducts in Revit, steps 1–7: equipment and the main run
- Open Floor Plans › L3 under Mechanical › HVAC and zoom to the apartment.
- Click Systems › Mechanical › Mechanical Equipment (ME). In the Type Selector pick
HVAC-Equipment-FCU-Daikin-7.1kW. In Properties type Elevation from Level3100, then click a point in the room. The space bar rotates the unit by 90°.
- Select the unit you have just placed. Revit 2027 draws two connector controls straight in the view, both labelled 800.0 x 200.0: the supply and the return spigot. Hover over one and Revit shows Create Duct; click it and the duct starts at that connector.
- Click Systems › HVAC › Air Terminal (AT). Pick
HVAC-AirTerminal-SAG : SAG-600x600, type Elevation from Level2700— the planned ceiling height — and click three points in the room.
- Click Systems › HVAC › Duct (DT). In the Type Selector pick
Rectangular Duct: TDC; the flange joint of the type decides which fittings appear later. - In Properties type Width
500, Height250and click Apply. This is what replaced the Options Bar of earlier releases. - Set the centreline height in Middle Elevation. The run sits above the 2,700 ceiling and matches the fan coil connector, so type
3225and click Apply. The three buttons on the left of the ribbon are still greyed because nothing is being drawn yet: Create Riser builds a vertical segment, while Inherit Elevation and Inherit Size make the duct take the elevation or the size of whatever you snap to.
Steps 8–14: branches, air terminals and flex duct
- Hover over the back of the fan coil until Revit snaps to the connector and click once for the start point, then drag north. A temporary dimension appears: type the length and press Enter instead of guessing with the mouse.
- Move east and click: Revit drops an elbow into the corner. Press Esc twice to end the run.
- Change size mid-run: start the Duct tool again, type Width
400, click Apply, then click the open end of the run you have just drawn and carry on. Revit inserts a transition between the two sizes.
- Branch off: still in the Duct tool, type Width
250, Height200, Apply. Hover over the centreline of the main until the snap appears, click, then drag west and click. Revit adds the tee and the transition at the junction.
- Join the diffusers with flex duct: click Systems › HVAC › Flex Duct (FD). Hover over a diffuser until the status bar reads
200 @ 2900 : Supply Air, click once, then click the centreline of the main. Revit draws the flex duct and adds a round tap on the main.
- Do the same for the other two diffusers: one onto the open end of the main, one onto the end of the branch. The other route gives the same result: select a diffuser, right-click its connector and choose Draw Flex Duct.
- Check: press F9 for the System Browser, where the new system appears under Mechanical, and open a 3D view to look over the whole run.
Where duct fittings revit places come from
Elbows, tees and transitions are not families you insert. Every duct type in Revit carries a Routing Preferences table: which family to use for the straight segment, the elbow, the tee, the transition and the flex connection, and in which size range. Revit reads that table as you draw.
Select a duct, click Edit Type, then Edit… on the Routing Preferences row.
So the fittings you get depend on the duct type, not on how carefully you draw. To swap a radius elbow for a square one, or a tap for a tee, duplicate the duct type and edit this table rather than deleting fittings and inserting your own. Building a type and loading fitting families works the same way on the pipe side, covered in pipe types in Revit.
Changing size and elevation after drawing
Ducts remain editable, but release 2027 handles it differently.
- One length: select it, type the new Width and Height in Properties, click Apply. Revit adds transitions at both ends.
- A whole run: edit one length at a time, or let Revit size the run from the airflow, as in how to size ducts in Revit. Hovering over a duct and pressing Tab selects the whole chain of ducts and fittings.
- Elevation mid-run: while drawing, type a new Middle Elevation in Properties and click Create Riser on the ribbon. Revit builds the vertical segment and two elbows. If the difference is too small for them, Revit reports "Line is too short", so increase the difference or reduce the duct size.
- Sizing from airflow is another job, done with Duct Sizing: see sizing ducts in Revit.
From CAD to Revit: flex duct in Revit, grilles and units
Draughtsmen coming from CAD look for a lisp routine for flex duct, a block for the grille, or a drawing of a ducted cassette unit to copy. In Revit each of those is already a command or a family with connectors.
| On CAD | In Revit 2027 |
|---|---|
| A lisp that draws two lines, then elbows and tees by hand | Duct (DT), called revit duct in English material: draw the centreline, the type supplies the fittings |
| A lisp that draws wavy flex duct | Flex Duct (FD), or right-click a connector › Draw Flex Duct |
| A block for the grille | An Air Terminal family with a connector that carries airflow |
| A block of a ducted cassette unit | A Mechanical Equipment family with supply, return, water and power connectors |
| Text notes for duct sizes | Duct tags, switched on with Tag on Placement while drawing |
| The architectural background | A linked Revit model, or a CAD file linked in |
The real difference is not the picture. Flex duct in Revit connects the diffuser connector to the main, so it belongs to the system and carries air. A wavy line on CAD is a line.
When the duct will not connect
| Symptom | Cause | Fix |
|---|---|---|
| The duct will not attach to the fan coil | The cursor missed the connector, or Automatically Connect is off | Switch Automatically Connect on; zoom in and hover until the status bar names the connector |
| A red box says "The segment is being drawn from the wrong side to connect to the location you indicated" | The point you clicked lies on the side the current segment cannot reach | Click Cancel, press Esc to end the run, then start a new run from the open end |
| Create Riser reports "Line is too short" | The elevation difference is smaller than two elbows need | Increase the difference, or reduce the size of the vertical piece |
| You type a new size but the duct still comes out at the old one | The value is still pending in Properties | Click Apply before you click the next point |
| The duct runs below the ceiling or through a beam | Middle Elevation was never set | Set Middle Elevation before drawing, or switch on Inherit Elevation when starting from a connector |
| The duct shows as a single line with no fittings | The view is at Coarse detail, or the run was drawn with Duct Placeholder | Set Detail Level to Medium or Fine; placeholders carry no fittings, so redraw with Duct |
| Flex duct will not land on the diffuser | The click missed the diffuser connector | Hover until the status bar reads Connector … : Supply Air, then click |
Three things people get wrong
| Often heard | What Revit 2027 does |
|---|---|
| Size and elevation are typed on the Options Bar | Release 2027 removed the Options Bar; Width, Height and Middle Elevation live in Properties and need Apply |
| A riser can only be drawn in a section | While drawing, change Middle Elevation and click Create Riser on the ribbon |
| Flex duct is only a drawing flourish | Flex duct joins connectors, so it belongs to the system and carries air like rigid duct |
| Elbows and tees have to be loaded and inserted | The duct type supplies them through Routing Preferences |
The run you have just built is the base for everything that follows: airflow and sizing, colour by system, sheet metal quantities. Systems themselves are covered in MEP systems in Revit.
Frequently asked questions
What changes for round duct?
Only the Type Selector: pick a Round Duct type and Properties replaces Width and Height with a single Diameter box. Every other step is the same.
Why does my duct show as one line?
The view is at Coarse detail level. Switch to Medium or Fine to see two lines and the fittings.
Can I draw quickly at concept stage, without fittings?
Use Duct Placeholder. It keeps size, elevation and system, but a corner is only a kink in a line.
How do I tell which system a duct belongs to?
Select it and read the Mechanical group in Properties: System Classification, System Type, System Name. For the whole file, press F9 for the System Browser.
How long should a flex duct be?
Revit does not cap it; the limit comes from the project specification. In the model a flex duct has vertices you can drag to reshape it.