SUMIF Question - leaving out specific cells

I'm currently working on a spreadsheet but can't get past one obstacle. The relevant columns and what they contain are as follows:
B - Name
C - Length
D - Room
F - Name
G - Total Length

I'm using the first columns (B, C, D) to calculate the values for column G. The problem I'm having is that I want to omit lengths from the total if they take place in a certain room.

For column G I'm using the function:

=SUM(SUMIF(B:B,F2,C:C))

This calculates the total for each person, but I want to omit lengths if they occured in Room "C7" from column D I don't know how to do this.

I hope I'm explaining this well enough, please see my attachment for an example. Thank you in advance for any help!