Airflow question

[mulpsmebeauty]

I'm just repairing my old PC and putting it in a new case with a 120mm fan at the back. How much space is required behind the PC in order for the air flow to remain relatively unrestricted?

Cheers.

 

[Stellar]

I would give it at least 4-6 inches. However more is better to disipate the heat. Ideally open air is best.