Poweredge M620/ M1000e space requirements

I have some R620 and M1000e in a lone 42u rack cabinet in my office &have some concerns regarding heat buildup and the distance between the rack cabinet and the walls of my office. I know these servers are designed to be set up in hot/cool aisles in a datacenter, but when used outside of a datacenter I couldn't find any distance specs or distance requirements in any of the manuals - especially the rear where hot air is vented out.

What is the minimum recommended distance that the cabinet should be positioned from the walls - does anyone know?