// Creates a FamilyInstance filter for elements that are family instances of the given family symbol in the document

// Find all family symbols whose name is "W10X49"
FilteredElementCollector collector = new FilteredElementCollector(document);
collector = collector.OfClass(typeof(FamilySymbol));

// Get Element Id for family symbol which will be used to find family instances
var query = from element in collector where element.Name == "W10X49" select element;
List<Element> famSyms = query.ToList<Element>();
ElementId symbolId = famSyms[0].Id;

// Create a FamilyInstance filter with the FamilySymbol Id
FamilyInstanceFilter filter = new FamilyInstanceFilter(document, symbolId);

// Apply the filter to the elements in the active document
collector = new FilteredElementCollector(document);
ICollection<Element> familyInstances = collector.WherePasses(filter).ToElements();

' Creates a FamilyInstance filter for elements that are family instances of the given family symbol in the document


' Find all family symbols whose name is "W10X49"
Dim collector As New FilteredElementCollector(document)
collector = collector.OfClass(GetType(FamilySymbol))

' Get Element Id for family symbol which will be used to find family instances
Dim query As System.Collections.Generic.IEnumerable(Of Autodesk.Revit.DB.Element)
query = From element In collector _
 Where element.Name = "Level 1" _
 Select element

Dim famSyms As List(Of Element) = query.ToList()
Dim symbolId As ElementId = famSyms(0).Id

' Create a FamilyInstance filter with the FamilySymbol Id
Dim filter As New FamilyInstanceFilter(document, symbolId)

' Apply the filter to the elements in the active document
collector = New FilteredElementCollector(document)
Dim familyInstances As ICollection(Of Element) = collector.WherePasses(filter).ToElements()