A computer system includes a computer rack configured to support a plurality of computer chassis in a computer stack region of the computer rack; a cooling plenum configured to draw air from a back side of a computer chassis supported in the computer rack and exhaust the air through an outlet port; and an airflow control member positioned between the cooling plenum and the computer stack region and providing an impedance to airflow between the computer stack region and the cooling plenum, said airflow control member providing a greater airflow impedance to a first portion of the computer stack region than to a second portion of the computer stack region.