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System Calculations

System calculations can negatively impact Revit performance. Review if the calculations are necessary at this moment. Consider turning them off and turning them on when applicable.

Calculations for Duct System Types

For duct system types, select All, Flow Only, None, or Performance and click OK.

  • All: All system-level calculations are computed.
  • Flow Only: Only the Flow parameter is computed.
  • None: The Flow parameter is not computed. Revit still maintains the logical sections in the duct system.
  • Performance: Neither the Flow parameter nor system-level calculations are computed.
  • Use Performance mode to improve Revit's performance when editing large MEP duct system networks. System propagation is disabled for every system in the project that uses the selected system type.

Note: The Duct Sizing tools are not available for systems where the Calculations parameter is set to Performance.

Calculations for Pipe System Types

For pipe system types, select Volume Only, None, or Performance and click OK.

  • Volume Only: Only the Volume parameter is computed.
  • None: The Volume parameter is not computed. Revit still maintains the logical sections in the pipe system.
  • Performance: Neither the Volume parameter nor system-level calculations are computed.
  • Use Performance mode to improve Revit's performance when editing large MEP pipe system networks. System propagation is disabled for every system in the project that uses the selected system type.

Note: The Pipe Sizing tools are not available for systems where the Calculations parameter is set to Performance.

source: Autodesk Help

Change calculation settings

Change the calculation method of the piping system or an HVAC system by following the steps below:

  1. Click on the piping system/HVAC system.
  2. Check the system name in the properties.
  3. In the project browser, go to the families section and open the section for piping systems.
  4. Select the piping system you checked earlier.
  5. Right-click and select "type properties."
  6. In the type properties, change the calculations to performance.

Source: Autodesk Support