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How to draw HVAC / ACMV Duct Systems in Revit

Drawing duct networks in 3D can be frustrating for first-time user, but will be much easier afterward (compared to using most conventional 2D software). Therefore, it is definitely worth investing some time to learn and master this skill – one which has already been set on track to revolutionise the construction industry – for our own satisfaction (to just be able to draw and see in 3D), not to mention other advantages offered by 3D perspectives: visualisation and presentation, coordination, computation and analyses etc. that Revit offers as its all-in-one package.

The guide below targets to simplify all steps needed to draw a complete duct network in the shortest possible manner. By the end of this compact session, we will be able to draw a duct network complete with fittings and terminals as shown in the photo below.


Step 1: Set the View’s Detail Level

Firstly, I prefer to set the view’s detail level to minimally “Medium” in order to see 2-line ducts (this applies to all views in Revit). This is done by clicking on the “resolution-like” icon on the bottom left corner.



Step 2: Set Routing Preference

The next step is to define the routing preferences. To do so, simply type the command “DT” (stands for Duct), and then at the properties pane, click “Edit Type”. (If you don’t see a properties pane, go to “View” tab > User Interface > Check “Properties”)



Then, in “Type Properties”, select “Edit” Routing Preferences:


Next, from the “Routing Preference” window, we need to select and assign a Revit Family File (RFA file) for each type of the fittings, if there is no selection option in the drop-down list, we will need to load the Duct Fitting Family


To load family, while selecting the type of fitting, click “Load Family”:


Then, navigate to your file directories to load the fitting families. Different types of fittings shall be available online. Your libraries for RFA files shall be available in your local PC, unless your Revit is a trial version, or unless you have missed installing the contents when you install Revit. Nonetheless, you may always visit Revit’s Content Download Site to download the entire libraries.


From the Revit official webpage above, Select the Revit Content Installer of your preferred language to download. Then, run the installer with administrator to install required libraries. As shown in the photo below, the table in the page indicates the file location to retrieve the RFA files once they are done installing. For example:


Imperial: <Content Path>\Libraries\English-Imperial\

Metric: <Content Path>\Libraries\English\US\


Note that “<Content Path>” above indicates the destination for the installation of you Revit software program files (which you have defined during your Revit installation). If you did not change any setting, the file location shall be defaulted to (C:\ProgramData\Autodesk\RVT <Version>).


e.g. – C:\ProgramData\Autodesk\RVT 2022\Libraries\English-Imperial\...


Navigate to the above-mentioned, your Revit’s <Content Path>, followed by Libraries, all the way to the RFA files as shown in the photos below. This file location may vary depending on where you install the contents into during your Revit installation. An example of directories is as follows:


C:\ProgramData\Autodesk\RVT 2022\Libraries\English-Imperial\Duct\Fittings\Rectangular


Alternatively, you may directly download the fittings provided in the zipped file below. (Note that it is always a safer practice to download from official Revit sites)

Duct Fittings
.zip
Download ZIP • 53.39MB

Once loaded, you will be able to select the loaded family from the drop-down list for each type of fittings (see Picture below). Take note that a “Transition” fitting will only show up in the “Transition” section only, as defined by the family category, so does any other types of fittings. This is the reason why the RFA files are by default organised into folders according to the fitting types. You can click the “+” button to add more selection to the routing preference, and use the arrow to adjust the priority level of preferences of a fitting. The higher-up preference will be adopted first when those fittings are available based on various constraints.



As a reference, picture above (summarised below) are some of the fittings that are most commonly needed in a rectangular duct network.

  • Elbow – 90 deg Smooth Elbow (1.0W)

  • Junction Type – Tee / Tap

  • Junction – Round Bevelled Tap Take-off (Tap) / Rectangular Bevelled Tap (Tap) / Rectangular Wye – Curved with Transition (Tee)

  • Transition – Pyramidal Transition

  • Cap – End Cap

Below are some illustrations for better recollection of these common fittings you certainly have seen before.

Cap – End Cap


Round Bevelled Tap Take-off


Rectangular Bevelled Tap


Pyramidal Transition


Rectangular Wye – Curved with Transition


90 deg Smooth Elbow (1.0W)


A few more things worth taking note include the smooth elbow turning radius (which defines how sharp or how smooth the turning of an elbow is), and the interchangeable selection between “Tap” and “Tee” fittings.


Smooth Elbow Turning Radius

  • 525/350 = 1.5W

  • 350/350 = 1.0W (Sharper turn, higher loss, less space is required)

  • 700/350 = 2.0W (Smoother turn, lower loss, more space is required)

On a side note, referring to the picture below, you may need to interchangeably use the routing preference between “Tap” and “Tee”, and change the Junction accordingly.



Step 3: Start Drawing a Duct

After the routing preference is set, it is time to start drawing. Use the command “DT” (stands for duct), and key in the required duct size and elevation. Middle elevation in this context, literally means the height from your reference level – depends on which level you set this to – to the middle of duct.

When 2 ducts join, the fitting from the preset routing preference will be inserted automatically, as long as the function “Automatically Connect” is opted (shall be opted by default).

Ducts may not be able to connect when they are off-alignment. Type the “AL” (stands for align) command, then click the destination/reference duct center line, followed by the source duct center line to align the 2. Revit may allow auto-generation of ducts that run diagonally, but will also require enough space for that.


Sometimes, two ducts of different elevations (different levels) cannot be joined be (prompted with all forms of messages) due to the limited space for the installation of fittings – always note that fittings such as smooth elbows require space. Distance out the 2 ducts by setting the higher duct at a higher elevation and the lower duct at a lower elevation, to allow for more space for connection. Then, after a connection is made, readjust to desired elevations. We may then change the radius of the elbow from a smoother elbow to a sharper elbow to save some space after the connection is made.

It is best to refer to the 3D window on a separate screen to see in 3D, the duct network updated in real-time. This helps us better understand what has happened, and whether what being drawn is what we wanted.

If ducting drawn is not shown (cannot be seen), try the following

  1. Ensure Ducting is turned on in Visibility Graphics (Command “VG”). Make sure ducts and fittings are checked, and turn off elements that might obscure the ducts such as roof or slab above.

  2. In the View Properties Pane (press ESC – to deselect any item), set the discipline to “Coordination”

  3. Set the Elevation of the duct and check whether the View Range (Command “VR”) of the View encompasses it. Make sure you add the duct in the correct plan view, at the correct level.

  4. Check the Revit Filter settings to rule out any desired parts being selectively filtered out

  5. It is easy to visualise all constructed works in a 3D view window by the side of your plan, so you will know what is going on. In your Revit ribbon, click the icon below to go to the 3D view:

Step 4: Continue drawing the Duct with the fittings auto-generated from the routing preferences

For a duct transition or change in duct elevation (Rise or bend up or Down), we just alter the parameters in the ribbon below, continuously, without the need to hit ESC. However, strangely, Revit requires the user to retain your cursor within the box indicated below when you type your figures in.


If you have hit “ESC”, to continue drawing from an existing duct, (1) click on the duct, and then (2) right-click near the “cross” icon at the “to-be-extended” end, and then (3) click “Draw Duct”.



Step 5: Air Terminals

To add air terminals, such as air grilles, louvers or diffusers, (1) type the command “AT”. From the properties pane on the left, (2) select the type of air terminals that you want to add and, (3) input the elevation of the air terminal with the base at the reference level. This is often the ceiling level with respect to the finish floor level.


Then, hover the previewing air terminal to where you want to place it in the reflected ceiling plan. Click to register it in any previewed spot. Then, use a flexible duct to connect from a rectangular rigid duct to the center of the air terminals. If you are to connect from a rigid duct directly to the air terminal (without a flex duct), make sure to align the center of air terminal with the center of duct, by using the “AL” (stands for Align) command.


Step 6: Draw a duct Vertically

If you add your air terminal below a duct with sufficient clearance for the fittings, the duct may connect automatically to the air terminal. In this case, Revit will automatically assume the duct size to be the same as air terminal’s connector size. You can edit this size in the family file of the air terminal by double-clicking the air terminal, or opt to use a transition.


With such, you certainly will come across instances whereby you need to draw a duct downward vertically from the duct to the air terminal. In order to do so, the easiest way is to do so is to draw in a section. (1) Click on the “View” tab, and then “Section”. You may assign it to a Keyboard Shortcut using the command “KS” (Stands for Keyboard Shortcut). (2) Then, draw the Section across the desired duct section, making sure it captures where we want to look at.


If you cannot see what you want to target at in the added section, make adjustments through the control methods below. First click on the added Section, then:

  1. Grip and hold the four-directional “Move” icon to move the section around.

  2. Toggle the view direction by clicking on the 2-directional arrow icon

  3. Adjust the view depth of the section by holding down the arrow and dragging the arrow on the box. You may want to reduce the view depth of the Section to exclude all non-targeted components, which may add to your confusion when you perform a connection.

Then, Double-clicking on the Arrow to go to the desired Section. Set the Detail level (Step 1) to at least “Medium”

Subsequently, draw the duct on the section, from the grille toward the duct. As mentioned, ensure enough space (marked ‘h’) to allow for duct fittings. Strangely, you may need to allow more space for ‘h’ than you actually need. Therefore, you may reduce this allowance further (if needed to), after the connection (Allow for more ‘h’ > Make the connection > Reduce ‘h’ if necessary).


Step 7: Draw a Flexible Duct

To draw a flexible duct, type the command, “FD”.

To set the routing preference for Flex Duct, click “Edit Type” on the Flex Duct Properties Pane.


If there is no option for the drop-down list, go to the Inset Tap, Load Family, and load the relevant round duct fittings into the project. An example of file location for the takeoff for flex duct can be found in the location below.


C:\ProgramData\Autodesk\RVT 2022\Libraries\English-Imperial\Duct\Fittings\Round\Taps