A computing system includes a chassis, one or more backplanes coupled to the chassis. Computing devices are coupled to the one or more backplanes. The one or more backplanes include backplane openings that allow air to pass from one side of the backplane to the other side of the backplane. Air channels are formed by adjacent circuit board assemblies of the computing devices and the one or more backplanes. Channel capping elements at least partially close the air channels.