the Cryorig H7 is designed to push air out the back. So one in the back to pull hot air away from the heatsink. Most cases have a top vent for atleast one 120mm and 2 lower front 120mm fan brackets. Least one fan in front to cool the HD's and or SSD's. The last depends on if you need GPU's cooled and have a door 120mm vent. If not last on top pulling hot air out of the case.