How much clearance does my HP Z440 Workstation need for proper ventilation?

The workstation requires at least 15.24 cm (6.00 in) of clearance at the front and back of the workstation — this is the minimum distance for all workstation models. You should also ensure that the ambient air temperature falls within the specified environmental limits and never block any vents or air intakes. For Windows 10 systems, an additional note specifies at least 10.2 cm (4 inch) clearance at the back of the unit and above the monitor. (Page 12)