What size case fan? Dunno.
1) How to measure the fan? Across the fan's shroud. (Surrounding Cage) Fan stood up, measure the Height, and Width.
2) Look at the label on the fan's center hub. Write the number down.
Now which of these CHASSIS fan numbers match?http://www.sparepartswarehouse.com/HP-Compaq,Business-Desktop-dc7100-dc7600-dc7700,Computer,Fans.aspx
Chassis Fan - 70mm x 70mm x 15mm.
70mm x 70mm is the height and width of the fan's shroud. (Surrounding cage) [ Chassis fan stood up ]
15mm is the Thickness of the fan shroud.
Nope, not that one.
B) 451144-001 Chassis Fan - 92mm x 25mm
C) 455310-001 Chassis Fan - 92mm x 25mm.