Creating Cross sectional view is very easy using cross section tool. Practically one can have cross section from any side and in all directions, but common practice is to draw either front or right side cross sectional view of the ducting network. Cross section is done in four steps. 

1.Place Cross Section Arrow.
2.Select the place where cross section is to be drawn
3.Select Cross Section Arrow
4.Select HVAC Components to be included in Cross Section 

Lets start with cross sectional arrow

From HVAC menu (HVAC/Cross Section/Cross-Sectional Arrow) select a cross section arrow which looks as shown below.
 

Select a unique tag. This same tag also appears at the bottom of cross section saying 'Cross Section At A-A'. 
Place arrow at a suitable position, indicating the direction to look at the ducting. 

Now we are ready to generate cross section