You should rethink the airflow in your case. The air is needed to go towards the CPU since that air cools down the heatsink, maybe you should change the case fan to blow inwards and put a dust trap before the fan. I could help more if I could see a plan of your airflow or even picture of the setup.
The CPU will overheat if you change the fan in any other configuration.
I have 3 front 120mm for intake, 1 back 120mm for exhaust, and 1 side 250mm for exhaust.