A system for restricting mixing of air in a data center includes a plurality of racks, each of the racks having a front face and a back face. The system includes an enclosure for collecting air released from the back faces of the plurality of racks, the enclosure configured to substantially contain the air in an area between the first row and the second row and having a roof panel coupled to the first row of racks and the second row of racks configured to span a distance between the first row of racks and the second row of racks. The enclosure is configured to maintain a first air pressure inside of the enclosure that is substantially equal to a second air pressure outside the enclosure.