Hi guys. I know this may be a stupid question to some of you but I'm still new to computers. I recently removed my Rear fan on my HP6000 pro tower to clean it and I'm not sure which way to install it back. Does the fan need to blow air out of the case or into the case? It also has a fan at the front which blows air into the CPU radiator/heat sink which is obvious to me but I'm not sure about the rear fan. Please help