Place a Route using Single Line mode

The procedure can begin with an air handling source placed preferably prior to the routing or it can be placed and connected later as stated in step no. 9.

Select a routing component tool; e.g. a rectangular duct ( Place Ducts).
The ribbon bar shows a contextual Placement > Place tab. A small segment of duct (icon) appears on the pointer, and the Place Component tool settings dialog appears.
Set the Placement options required in drawing a route.
Ensure the required duct type catalog is activated in Place Component dialog.
Check the (Single-Line Mode) option on the Placement > Place > Flex Duct Options tab to begin with route in a single line.
The Placement (Justification) options automatically void for single line mode.
Click in the view to select data point to locate the route start point.
The free end of the new duct is dynamically attached to the pointer.
Select the end point/next point for the new duct.
The duct route appears in a single line presentation. The nodes appear at turns and connections signify their type (viewed with mouse hover).
To draw a diverted duct segment, change the route's direction by selecting another point that is not inline with the previously selected points.
The tool automatically places a Bend at the node joining the last segments placed.

Note: The Bend typically is the default fitting, and when promoted would result as an elbow set in Auto Fitting option. You can however, override the node catalog to suit your design.

Segment 2 -> 3: Rectangular Duct size changes from 20x16 to 16x14; Segment 3 -> 4: Duct shape changes from Rectangular to Round;

Tip: If the route changes direction and size, a Branch is automatically placed to connect the changing route. If the shape is round (duct), the branch incorporates a coupling fitting at the node.

Note: While placing a different size duct segment on the fly, ensure the Size on the Placement Options tab is unchecked to accept different dimensions being set in the Place Component dialog.
(Optional) Connect the duct terminal to an opening / exhaust fitting such as a diffuser placed at an elevation by setting the base offset and type (rigid or flex) in case of round duct.
The diffuser gets hooked up in the route at vertical drop value of given offset.
Reset to complete the route.
The route will also have endcap symbols added at the open terminals.
To add a source of air handling, place an equipment, such as fan or AHU connecting it at the beginning of the route.
The single line route is ready for analysis or manipulating.

Using the Duct System Sizing the single line routes can be rebuilt using the calculation for altered properties and dimensions in the Fitting Loss Coefficient Summary interface of duct sizing utility and be promoted to 3D.

Note: Single line design is only a schematic representation that utilizes a nodal approach to reflect changes in direction (elbows), changes in size (reducers), branches (take-offs, tees) and changes in shape (transitions). No actual geometry or component data is attributed to these nodes until after calculations and a promote to 3D is used through the Duct Sizing process, therefore IFC export should be used on the 3D model only. To achieve a single line representation in drawing output the rules available in the Dynamic View capabilities to create a single line view should be used.

Place a Route using Single Line mode

Segment 2 -> 3: Rectangular Duct size changes from 20x16 to 16x14; Segment 3 -> 4: Duct shape changes from Rectangular to Round;