An environmental control unit for a personal computer tower case includes an enclosure configured to substantially enclose the tower case and an air conditioning unit configured to draw air from a first region of the enclosure, cool the air to within a selected range of temperatures, and output the air into a second region of the enclosure. The enclosure includes a gasket disposed between an outer wall of the tower case and an inner surface of the enclosure, for preventing circulation of air within the enclosure and around an exterior of the case. The enclosure may also include a port for access to a front side of the personal computer case, and an aperture in a back wall of the enclosure for passage of cables. The aperture is configured to permit passage of the cables while limiting passage of air.