Replace empty by 0 - excel

Question

I want to check all cells in columns D to O. If the cell is empty, replace it by a hard zero.
I have this code:
Sub replace()
Dim rng As Range, cell As Range
Dim aantalrijen As Long
With Worksheets("Schaduwblad")
aantalrijen = .Range("A1", .Range("A1").End(xlDown)).Cells.Count - 1
Set rng = .Range(.Cells(2, "D"), .Cells(aantalrijen, "O"))
For Each cell In rng
cell = WorksheetFunction.Substitute(cell, "", "0")
Next
End With
End Sub
This code hangs during processing. Only option is to end the routine by pressing Escape.

Answer 1

You don't need to loop through all the cells. Let Excel find the empties with .SpecialCells:
On Error Resume Next
rng.SpecialCells(xlCellTypeBlanks, xlCellTypeConstants).Value = 0
On Error GoTo 0
The error trap is required in case no empty cells are found.
So your whole routine could be replaced with:
Sub replace()
On Error Resume Next
With Worksheets("Schaduwblad")
.Range(.Cells(2, "D"), .Cells(.Cells(.Rows.Count, 1).End(xlUp).Row, "O")) _
.SpecialCells(xlCellTypeBlanks, xlCellTypeConstants).Value = 0
End With
On Error GoTo 0
End Sub
Further to your comment below, here is a version of the same code, but working on a row-by-row basis. To test this, I built a 227,000 x 15 block of data and then using a random number generator punched 100,000 holes into it, emptying those cells. I then ran the following code, which took 33 seconds to fill those 100,000 holes back in.
Sub replace()
Dim rangesection As Range
On Error Resume Next
With Worksheets("Schaduwblad")
For Each rangesection In .Range(.Cells(2, "D"), .Cells(.Cells(.Rows.Count, 1).End(xlUp).Row, "O")).Rows
rangesection.SpecialCells(xlCellTypeBlanks, xlCellTypeConstants).Value = 0
Next
End With
On Error GoTo 0
End Sub

Answer 2

I've never used the substitute methode.. I would do this by checking if cell is empty with the IsEmpty() function.
So yo can swap
cell = WorksheetFunction.Substitute(cell, "", "0")
with
If IsEmpty(cell) Then cell.value = 0
Full code:
Sub replace()
Dim rng As Range, cell As Range
Dim aantalrijen As Long
With Application.ThisWorkbook.Worksheets("Schaduwblad")
aantalrijen = .Range("A1", .Range("A1").End(xlDown)).Cells.Count - 1
Set rng = .Range(.Cells(2, "D"), .Cells(aantalrijen, "O"))
For Each cell In rng
If IsEmpty(cell) Then cell.value = 0
Next
End With
End Sub