There is a common problem with the Revit MEP Air
Terminal Family. When we place an Air Terminal, we want to be able
to align it to the edge of a ceiling grid. The problem is, that when
we use the align tool to align the terminal to the grid, there is no
reference line on the edge of the air terminal to align to. See
reflected ceiling illustration below.

With this month’s AEC Article, I am assuming that you are an MEP
Engineer who recently started using Revit and you have a linked
Revit Architectural Model that you will be adding your MEP systems
to.
What we want to do here is edit this air terminal family so that
there are reference lines on all sides of the air terminal. Once we
do this, it will allow us to use the Align tool to align the air
terminals to the ceiling grids without having to use the Move tool.
Our first step is to edit the air terminal family. Inside the
family editor, you should see something like this:

On the project browser on the left, double-click on: Views all >
Floor Plans > Ref. Level, to go to the floor plan view of the
terminal. You should see the floor plan like this:

The next thing we need to do is create some reference lines.
These reference lines are going to allow us to align the edge
of the terminal to the ceiling grid.
1. Draw reference lines on each outer side of the air terminal like
this (I am showing the reference lines in bold red dashed for
clarity).

2. Draw a dimension going from the left reference line
to the right reference line. When dimensioning, make
sure that you are selecting the actual reference line and not the
other symbolic line or mass element. Use the TAB key to cycle
through the selections until you hit the reference line. If you
do not dimension from reference line to reference line, these
reference lines will not be parametric when you resize the air
terminal.
3. Once you have the dimension, make another dimension that goes
from the Left reference line, to the center
reference plane, to the right reference line.
See Illustration below.

4. Click the 1’-0” dimension and click the EQ. symbol so that you
have this:

5. Click the 2’-0” dimension and change the label to “Width.”

You should have this:

Repeat steps 2-5. You should end up with this:

The dimensions should be going from reference line to
reference line, as explained in step 2. Again, use the TAB key to
cycle through the selection.
If you did the above correctly, you can click on Family types on the
left and change the width to 2’-6” and click Apply, your reference
lines will move with the sides of the air terminal. Change the width
to 2’-0” again and click apply so it is correct.

Finally, click finish sketch on the left side of the screen and
click the
button
on the left. You may get a dialogue box like this:

Go ahead and click Yes.
4. Now. For the final test, use the align tool to align an air
terminal to the ceiling grid.

As you can see, I have just aligned the edge of my air terminal with
my ceiling grid. If you later decide to create a new family type and
resize the air terminal, your reference lines should automatically
resize with the air terminal geometry.