Use the Mechanical Equipment tool and the Generate Layout tool to place pipe in a system.
This video demonstrates the following:
The process of creating a pipe system in Revit MEP involves 3 main steps: adding equipment, creating the logical system, and adding pipe to create the physical system.
For example, to create a hydronic piping system, begin by placing water source heat pumps. To do this, you select Mechanical Equipment, and then select a specific type from the Type Selector. When placing these elements in the model, you can rotate them by pressing the space bar. Now place a boiler in the model using the same basic method you used to place the heat pump. Next, create the logical system. Begin by selecting one of the heat pumps and specifying the type of system. For the equipment, select the boiler. Finally, edit the system to add the second heat pump.
After creating the logical system, you can edit it by adding or removing components. Revit MEP allows you to create the logical system before laying out the physical system. Finally, click the Generate Layout tool to create and route piping that connects the pumps and the boiler. When multiple layout solutions are possible, you can cycle through them using the controls on the Options Bar.
After you've completed the basic layout of the system, you can modify pipe routing as needed. This same basic workflow for creating a pipe system can also be used to create mechanical air systems.