Revit MEP - Free Size Parameter

If you use the Free Size parameter instead of Size you might notice a subtle anomaly.

In elevation views where we only see one dimension of a duct Free Size does not switch between WxH and HxW, the Size parameter does switch. In other views they both display width x height. In section or elevations that show the profile of a duct both dimensions are measurable and each parameter is consistent, they default to Width x Height.

It does seem like an oversight on their part, they ought to be consistent whether we use Size or Free Size.

Revit MEP - Duct Size in Tags

This is subtle but RME changes how the size of a duct is listed in the tag according to the view orientation of the view that you place your tags in. In plan you get this for a 36" wide x 24" high duct.


In elevation/section however you get this for the same duct.


This convention is defined by the practice of listing the visible (what we see in the view) dimension first. In plan width is visible so it is first. In elevation/section the height is visible and therefore first in the tag values.

MEP Wire Sizing Feedback Request

Echoing copy from an AUGI post.

The Revit MEP User Assistance team (the group responsible for help and tutorials) has been working on documenting some of the calculation methods that are used in Revit MEP. We are posting some of the information in a “pre-release” state to try and get feedback on how we can better meet your needs.

The first of these reviews is on how duct sizing in Revit MEP works, with additional sections to follow as we get them completed. Any and all comments are welcomed about the information we provide in the attached files.

If the contents of these documents don’t apply to you, please don’t feel like you need to review them (i.e. if you're the electrical person, don’t review duct sizing stuff), but if you know someone who might be interested please let them know. The more feedback we get the better we can make the documentation.

Vist the Inside the System blog

Thanks for your help!

Karen Smith (Autodesk)

Duct Size Parameter - Inches - Revit MEP

If you used AutoCAD before using Revit you likely went through a bit of withdrawal from using inches as a base drawing unit. With Revit you had to get used to typing 0 space 6 for 0'-6" or 0 dash 6. Well in Revit MEP there is one instance at least where you get to enter relevant values when working through your design.

First if you are interested I posted a little video overview of this subject. Otherwise read on...

I am referring to the duct size parameters as the title suggests. In the Family Editor > Family Types dialog we can choose to Add Parameters to our family. Aside from providing a clever name we also can choose the Discipline > HVAC which in turn offers quite a few choices for "Type of Parameter".


When you choose Type of Parameter: Duct Size, Revit will require you to enter values in inches, which is easier since most duct sizes are referred to by their size in inches.

There's a catch though if you like to add parameters by using the Associate Family Parameter "sneaky button" in the properties of elements in the Family Editor.


This route precludes the use of the HVAC Discipline, Type of Parameter choices as it defaults to common and its subset of Types of Parameters. Not FAIR I say! I'm sure it is just an oversight!

To use it you need to start with Family Types > then Add Parameter. Then you can Associate the family parameter with the Element's parameter.