With six 120mm fans and an 18" depth, the Cool-stack II has the power - and the reach - to pull up to 130 CFM of hot air out of tightly-packed racks while generating low noise levels. The Cool-stack II has two temperature-controlled speeds, and will change speeds as rack temperature changes to satisfy the requirements of residential and commercial installations; in either case, heated air can be expelled through the perforated front panel or through ports on the top or rear panels using optional exhaust kits. Tubing and fittings in the kits allow the Cool-stack II to channel exhausted hot air from its top and rear exhaust ports to nearby closets, attics, utility rooms, etc.