You download a fan coil family, place it on the plan and drag a duct towards it. The duct runs straight through the box, nothing snaps, and the System Browser still reports an empty system.
MEP equipment families in Revit differ from architectural families in exactly that respect. The solid is only the shell; what matters is the connector — the point that declares whether this is supply or return air, chilled water or condensate, and at what voltage. This article walks through 15 steps that build a complete ducted fan coil unit with six connectors, each step saying what to click and what appears. To learn the whole MEP workflow on one sample building, see the Institute's Revit MEP course.
Generic family skills — reference planes, extrusions, parameters — are covered in how to create a family in Revit; this article only covers the MEP-specific half.
What makes an MEP equipment family different
A door needs the right geometry and the right parameters. An MEP component needs one more layer: every Revit family connector carries a discipline, a system classification, a flow direction and a size.
Autodesk puts it bluntly on the Connectors page: "Components created without connectors cannot participate in a system topology". No connector means no duct snapping, no flow totals, no panel loads.
Revit 2027 offers five connector types, all on the Connectors panel of the Create tab in the Family Editor.
| Button | Used for |
|---|---|
| Duct Connector | ducts, duct fittings, air terminals |
| Pipe Connector | pipes, valves, plumbing fixtures |
| Electrical Connector | any electrical link: power, data, fire alarm |
| Cable Tray Connector | cable tray and tray fittings |
| Conduit Connector | conduit, as a single point or a whole surface |
Pick the wrong type and you start over. Autodesk is explicit: "After this selection is made, it cannot be changed without first deleting the connector and adding it again with the correct discipline".
Preparation: metric family templates and a file to follow along
You need the metric family templates that ship with Revit and a project to test the load. For the exercise file, see Revit MEP sample files.
The worked example is a ducted fan coil unit, 1,000 × 500 × 250: supply air at one end, return air at the other, chilled water flow and return plus condensate on the front face, and power on top. Placing and connecting it inside a project is covered in VRF and fan coil units in Revit.
Steps 1–5: open the template, set the category, build a parametric box
Step 1. Go to File › New › Family. The New Family - Select Template File dialog opens in the English-Imperial folder, which holds the inch templates. Switch to the English folder next to it, where every file carries the Metric prefix.
Step 2. Select Metric Mechanical Equipment.rft and click Open. The same folder holds Metric Mechanical Equipment ceiling based.rft and ... wall based.rft for units fixed to a ceiling or wall; rod-hung equipment uses the plain template.
Step 3. On the Create tab, Properties panel, click Family Category and Parameters. The category is already Mechanical Equipment, which is what allows the unit to be chosen as the equipment of a system. The Part Type box defaults to Normal, for free-standing equipment.
Step 4. Open the Ref. Level plan. Draw four reference planes around the origin with Reference Plane (RP), dimension them with Aligned Dimension (DI) and click EQ on both symmetrical pairs. Select each overall dimension and use the Label Dimension panel to create the type parameters Chieu_dai and Chieu_sau; do the same in the Front elevation for Chieu_cao.
Step 5. Click Extrusion, sketch a rectangle onto the four planes, click all four padlocks and finish the sketch. In the solid's Properties, click the small square at the end of the Extrusion End row and map it to Chieu_cao.
Steps 6–9: add the duct connectors
Step 6. Open the 3D view and click Duct Connector on the Create tab. The ribbon switches to Modify | Place Duct Connector with a single Placement panel offering Face and Work Plane. The status bar reads "Place a connector by picking an edge loop of a face".
This is where people get stuck: hovering in the middle of a face highlights nothing, because Revit wants an edge loop. Hover over an edge, press Tab to swap between the two faces sharing it, and click only when the four edges of the face you want are highlighted.
Step 7. The connector lands in the centre of the face with Width and Height labels drawn in the view. The default size is 304.8 × 304.8 — 12 inches — even in a metric template, so the next step is not optional.
Step 8. With the connector selected, set three fields: System Classification to Supply Air, Flow Direction from Bidirectional to Out because air leaves the unit, and leave Flow Configuration on Calculated so Revit adds up the flow of the terminals downstream.
Step 9. Click the small square at the end of the Width row. The Associate Family Parameter dialog lists parameters of the same data type; use the button at the bottom left to create Gio_cap_rong as a Type parameter and click OK twice. Repeat for Height, then repeat steps 6–9 on the opposite face with Return Air, direction In and the parameters Gio_hoi_rong and Gio_hoi_cao.
Once mapped, both boxes turn grey: the values are edited in Family Types, not on the connector.
Steps 10–13: pipe connectors for water, an electrical connector for power
All three water connections sit on the same face, and a face takes only one connector, at its centre. The tidy answer is to place them on a named work plane.
Step 10. In the plan, select the front reference plane, type Mat_truoc into the Name box and click Apply. The named plane then appears in the list used by the next step.
Step 11. Click Pipe Connector and choose Work Plane on the Placement panel. In the Work Plane dialog pick Mat_truoc from the Name list and click OK. The connector lands at the origin of that plane; use Move (MV) to slide it to the real stub position.
Step 12. Set each pipe connector: chilled water flow as Hydronic Supply direction In, the return as Hydronic Return direction Out, condensate as Sanitary direction Out. Map Diameter to DN_nuoc_cap, DN_nuoc_hoi and DN_nuoc_xa the way step 9 did. With Sanitary and domestic classifications, Properties gains a Fixture Units row.
The Allow Slope Adjustments box matters for drainage: leave it clear and a sloped pipe will report an angle error and disconnect.
Step 13. Click Electrical Connector and place it on the top face the way step 6 did. System Type defaults to Power, and Properties is then nearly empty. Switch it to Power - Balanced and the full set appears: Number of Poles, Power Factor State, Load Classification, Voltage, Apparent Power, Power Factor.
Set Number of Poles to 1, Voltage to 220 V and Apparent Power to 120 VA, then map the last two to Dien_ap and Cong_suat. The Load Classification cell has a browse button that opens Load Classifications; choose HVAC so the load lands in the right group on the panel schedule.
Steps 14–15: flex the family, then load it into a project
Step 14. Click Family Types. The table collects every parameter created so far: Dimensions for the box and the connector sizes, Electrical Engineering for voltage, Electrical - Loads for apparent power.
Change Chieu_dai from 1,000 to 1,400 and click Apply. The box grows and both duct connectors follow the end faces, because they are hosted by faces rather than by coordinates.
Flexing is the step people skip, and skipping it means the geometry breaks halfway through a live project instead. It is also the moment to save MEP equipment families in Revit under a library name your team will recognise.
Step 15. Save the family under a name without diacritics, then click Load into Project. The Load into Projects dialog lists every open project and family; tick the target and click OK.
In the project, place the unit with Systems › Mechanical › Mechanical Equipment (shortcut ME) and select it. Revit draws a label for each connector: system, size and flow direction — the quickest check that the family is declared correctly.
According to About Connector Labels, clicking the system icon on a label starts the routing command and inherits the size and elevation from the connector. Revit 2027 also has an Analyze › MEP Connections › Show Connector Controls toggle that displays connector number, type and size in the view.
What to set on each connector
The six connectors of the example end up like this.
| Connector | System Classification / Type | Flow Direction | Size | Mapped parameter |
|---|---|---|---|---|
| Supply air | Supply Air | Out | 400 × 200 | Gio_cap_rong, Gio_cap_cao |
| Return air | Return Air | In | 450 × 200 | Gio_hoi_rong, Gio_hoi_cao |
| Chilled water flow | Hydronic Supply | In | DN 25 | DN_nuoc_cap |
| Chilled water return | Hydronic Return | Out | DN 25 | DN_nuoc_hoi |
| Condensate | Sanitary | Out | DN 32 | DN_nuoc_xa |
| Power | Power - Balanced | — | 220 V, 120 VA | Dien_ap, Cong_suat |
Three things trip people up. Flow Direction describes the medium, not the drawing direction: two connectors that meet must be opposite. The first connector of each discipline becomes the primary one, and Re-assign Primary changes that. Finally, naming each point in Connector Description pays off later, because Connect Into then lists names instead of "Connector 3".
From CAD blocks to Revit families
The usual question is whether a block can be converted straight into a family. The geometry can; the information cannot.
| In CAD | In Revit | Extra work |
|---|---|---|
| 2D block of the unit | tracing reference | delete the imported CAD afterwards |
| Plan symbol | symbolic lines or a nested annotation | the symbol must keep its orientation when the unit rotates |
| A note reading "duct 400×200" | the connector size | the size flows into the duct as you draw |
That last row is where Revit wins: the number lives in the connector, not in a text string, so drawings and schedules cannot drift apart. Logical systems are covered in Revit MEP systems.
When the duct will not connect to the unit
| Symptom | Cause | Fix |
|---|---|---|
| No snap point when a duct approaches | no connector, or it sits inside the solid | place it on the outer face and check in 3D |
| It connects but the system reports errors | both connectors share a Flow Direction | one end Out, the other In |
| The unit is missing from the system equipment list | the family category is not Mechanical or Electrical Equipment | change it in Family Category and Parameters and reload |
| The duct comes out the wrong size | the connector is still at the default 304.8 | set Width, Height, Diameter and map them to parameters |
| Parameters change but the connector stays put | the connector sits on a free-standing plane | replace it with the Face option, or tie the plane to a parameter |
Three things you often hear
| What you hear | What Revit 2027 does |
|---|---|
| MEP families must be modelled in detail | A correctly sized box with correct connectors is enough for coordination; extra detail only bloats the file |
| Any connector type will do, change it later | It cannot be changed: delete it and place the right type |
| Drop a connector on and the duct sizes itself | The default is 304.8 mm; leave it and the duct is drawn at that size |
Frequently asked questions
Which category should equipment families use?
Mechanical Equipment for air handling units, fans and pumps; Electrical Equipment for panels. Only these two can be selected as the equipment of a system.
How does a face connector differ from a work plane connector?
A face connector sits at the centre of the face and follows it when the solid changes size, but a face takes one connector only. A work plane takes several, and they can be moved freely. Map connector sizes to Type parameters and flow or load to Instance parameters.
How long does the first MEP family take?
A simple unit like this one takes about half a day if you already build ordinary families. The slow part is not the geometry — it is declaring the right system and the right direction on every connector.