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System Calculations

System-level calculations in Revit can significantly affect model performance—especially in large MEP projects. This rule reminds you to evaluate whether system calculations are needed at this stage of your project.

If real-time calculations aren't necessary, it's recommended to switch them off temporarily to improve performance and reduce lag during modeling.

Why This Matters

Each system type (ducts, pipes) can automatically calculate values like flow or volume. While helpful during coordination and system sizing, these calculations can:

  • Cause slowdowns in large models
  • Trigger delays when editing system components
  • Disable manual overrides or cause unwanted system propagation

By setting system types to Performance mode, Revit stops propagating system data, reducing the processing overhead.

Calculation Options – Duct Systems

In the Type Properties of each Duct System Type, you can choose:

  • All: All system-level calculations are active.
  • Flow Only: Only flow rates are calculated.
  • None: Flow is not calculated, but logical system sections are maintained.
  • Performance: No calculations or propagation; ideal for performance optimization.

💡 Use Performance for large or heavily segmented duct systems during early-stage design or bulk modeling tasks.

⚠️ Duct sizing tools are disabled when using Performance mode.

Calculation Options – Pipe Systems

Pipe System Types offer slightly different settings:

  • Volume Only: Only volume is calculated.
  • None: No volume calculation, but system structure is preserved.
  • Performance: Disables all calculations and propagation for better performance.

⚠️ Pipe sizing tools are not available when using Performance mode.

How to Change Calculation Settings

To adjust the calculation method for a system type:

  1. Click on a system element (e.g., pipe or duct).
  2. Check its System Type in the Properties palette.
  3. In the Project Browser, navigate to Families → Duct Systems or Pipe Systems.
  4. Find the matching system type, right-click, and choose Type Properties.
  5. In the Type Properties dialog, locate the Calculations setting.
  6. Set it to Performance (or another level depending on your current needs).
  7. Click OK to apply.

📘 Source: Autodesk Help
📘 Source: Autodesk Support

DAQS Recommendation

Unless you're actively performing system sizing or flow validation:

✅ Set system calculations to Performance during early modeling phases or in large-scale models.

This improves responsiveness and reduces the risk of slowdowns when placing, modifying, or copying MEP elements.