The Rack Air Containment System (RACS) is a mechanical ducting system that attaches to the front or rear of an enclosure to provide increased cooling capacity. The RACS is a modular system that works with APC NetShelter SX enclosures and InRow cooling units to provide maximum cooling predictability, capacity, and efficiency. By attaching the RACS to the rear of the NetShelter SX, air expelled from IT equipment is forced to pass through the cooling unit, where it is conditioned. This ensures that warm exhaust air does not enter the air inlets of installed servers. Redundant configurations allow maximum availability. Optional front containment configurations reduce noise and provide additional control of air flow. The RACS components can be attached to a single enclosure or a group of enclosures.