The default system "[Element Name]" is now over 50 elements. To improve performance, Revit is no longer calculating the critical path pressure drop and the more complex duct sizing has been disabled. If you want to use these features, you must define logical systems in the model instead of using the default system.

public static FailureDefinitionId DefaultSystemOver50Elems { get; }

Public Shared ReadOnly Property DefaultSystemOver50Elems As FailureDefinitionId
	Get

public:
static property FailureDefinitionId^ DefaultSystemOver50Elems {
	FailureDefinitionId^ get ();
}