Sum all column values after each import - excel

Question

My current code reads manhours(integer values) from different workbooks and exports them to a column in a master output sheet. After each import I want to sum the total amount of hours that is exported to the main sheet, however,
I'm unsure as to how to do so without summing the entire column. Additionally, after summing up the total manhours from each sheet, I want to compare this value with that from the sheet to confirm if I copied all the rows correctly.
My outputsheet looks like this after each import:
data----------data----------hours(sheet1)
data----------data----------hours(sheet1)
data----------data----------hours(sheet1)
data----------data----------hours(sheet2)
data----------data----------hours(sheet2)
My current code looks like this:
Option Explicit
Sub manhours()
Dim Files As Variant
Dim i As Long
Dim j As Long
Dim sh As worksheet
Dim outputsheet As Worksheet
Dim erow As long
Dim manhours As Long
Workbooks.Open Files(i)
Set sh = Sheets("manhours")
For j = 2 to 30
erow = outputsheet.Cells(Rows.Count, 1).End(xlUp).Offset(1, 0).Row 'empty row
If IsEmpty(Cells(j, 3) = False Then
outputsheet.Cells(erow, 1).Resize(1, 2).Value = sh.Cells(j, 1).Resize(1, 2).Value 'copies the first 2 columns containing other data values
outputsheet.Cells(erow, 3) = sh.Cells(j, 3) 'column 3 from sh contains manhours
End If
Next j
manhours = Application.WorksheetFunction.Sum(outputsheet.Columns(3)) 'unsure how to sum only the values from sheet i and not the entire column
MsgBox (manhours) ' msgbox than gives the total man hours
manhours = sh.Range("C31") 'total manhours from sheet is in sh.Range("C31")
'MsgBox (True/False) 'unsure how to do this
Next i
End Sub

Answer 1

I don't see the need to use WorksheetFunction.Sum here.
One option: keep a running sum, like this:
manhours = 0 ' reset manhours to 0 for each new file
For j = 2 to 30
If Not IsEmpty(sh.Cells(j, 3).Value) Then
...
outputsheet.Cells(erow, 3).Value = sh.Cells(j, 3).Value
manhours = manhours + sh.Cells(j, 3).Value ' could add an IsNumeric check here to avoid a Type Mismatch
End If
Next j
MsgBox manhours ' no parentheses
MsgBox manhours = sh.Range("C31").Value