It all depends on the system, size and rpm of the fans you are using, make sure you have enough fans blowing fresh air in and fans sucking the hot air out (positive air flow)
It doesn't hurt to have an extra fan on top if you have the option on your case, it may help on the temperature of the system, as well as on the CPU itself.
Good fans are cheap now days, go with 120mm or 140mm from Cougar, Noctua or Corsair.
It all depends on the system, size and rpm of the fans you are using, make sure you have enough fans blowing fresh air in and fans sucking the hot air out (positive air flow)
It doesn't hurt to have an extra fan on top if you have the option on your case, it may help on the temperature of the system, as well as on the CPU itself.
Good fans are cheap now days, go with 120mm or 140mm from Cougar, Noctua or Corsair.